Doc. no. | N3012=09-0202
Date: | 2009-11-08
Project: | Programming Language C++
Reply to: | Howard Hinnant <howard.hinnant@gmail.com>

# C++ Standard Library Defect Report List (Revision R68)

Reference ISO/IEC IS 14882:2003(E)

Also see:

- Table of Contents for all library issues.
- Index by Section for all library issues.
- Index by Status for all library issues.
- Library Active Issues List
- Library Closed Issues List

This document contains only library issues which have been closed by the Library Working Group (LWG) after being found to be defects in the standard. That is, issues which have a status of DR, TC, or RR. See the Library Closed Issues List for issues closed as non-defects. See the Library Active Issues List for active issues and more information. The introductory material in that document also applies to this document.

## Revision History

- R68: 2009-11-06 post-Santa Cruz mailing.
  - Summary:
    - 205 open issues, down by 77.
    - 1055 closed issues, up by 120.
    - 1260 issues total, up by 43.
  - Details:
    - Added the following Dup issues: 1230.
    - Added the following NAD issues: 1229, 1236, 1243.
    - Added the following NAD Editorial issues: 1232.
    - Added the following NAD Future issues: 1235, 1242, 1248.
    - Added the following New issues: 1218, 1219, 1221, 1222, 1223, 1224, 1225, 1234, 1240, 1244, 1245, 1246, 1249, 1250, 1251, 1252, 1253, 1254, 1255, 1256, 1257, 1258, 1259, 1260.
    - Added the following Open issues: 1228.
    - Added the following Ready issues: 1227, 1237.
    - Added the following Review issues: 1247.
    - Added the following Tentatively NAD Editorial issues: 1233, 1239.
    - Added the following Tentatively NAD Future issues: 1238.
    - Added the following Tentatively Ready issues: 1220, 1226, 1231, 1241.
    - Changed the following issues from New to NAD: 1132, 1148.
    - Changed the following issues from Open to NAD: 96, 458, 463, 916, 917, 919, 955, 977, 1009, 1020, 1035, 1042, 1051, 1064.
    - Changed the following issues from Review to NAD: 668, 930, 1091, 1102.
    - Changed the following issues from Tentatively NAD to NAD: 588, 617, 971.
    - Changed the following issues from Tentatively NAD Future to NAD: 1062.
    - Changed the following issues from NAD Concepts to NAD Editorial: 1143.
    - Changed the following issues from New to NAD Editorial: 1116, 1117, 1122, 1129, 1145, 1146, 1147, 1155, 1166, 1172, 1174, 1179, 1195, 1196.
    - Changed the following issues from Open to NAD Editorial: 431, 580, 635, 719, 823, 827, 879, 880, 908, 923, 924, 926, 944, 947, 958, 1046, 1048, 1054, 1055, 1075, 1088, 1160, 1161, 1162, 1163, 1165.
    - Changed the following issues from Review to NAD Editorial: 828, 897, 976, 1043, 1047, 1049, 1050.
    - Changed the following issues from New to NAD Future: 1120, 1150, 1184, 1203, 1217.
    - Changed the following issues from Open to NAD Future: 484, 532, 851, 933, 935, 936, 961, 1041, 1053.
    - Changed the following issues from Tentatively NAD Future to NAD Future: 1031.
    - Changed the following issues from New to Open: 1118, 1119, 1151, 1153, 1156, 1171, 1173, 1183, 1191, 1211.
    - Changed the following issues from Ready to Open: 430, 834.
    - Changed the following issues from Review to Open: 397, 408, 835.
    - Changed the following issues from Tentatively NAD to Open: 625.
    - Changed the following issues from New to Ready: 1123, 1134, 1135, 1136, 1144, 1177, 1194, 1204, 1216.
    - Changed the following issues from Open to Ready: 296, 471, 485, 539, 816, 860, 865, 872, 920, 932, 939, 940, 960, 963, 974, 978, 1011, 1030, 1079, 1098.
    - Changed the following issues from Review to Ready: 473, 671, 836, 854, 868, 871, 889, 893, 921, 950, 954, 957, 962, 967, 968, 983, 1052, 1094, 1095, 1097, 1100, 1104, 1157.
    - Changed the following issues from New to Review: 1130.
    - Changed the following issues from Open to Review: 556, 631, 676, 727, 929.
    - Changed the following issues from Open to Tentatively NAD: 1056, 1099.
    - Changed the following issues from New to Tentatively NAD Concepts: 1186.
    - Changed the following issues from New to Tentatively NAD Editorial: 1115.
    - Changed the following issues from New to Tentatively NAD Future: 1121, 1201.
    - Changed the following issues from Open to Tentatively NAD Future: 1112.
    - Changed the following issues from New to Tentatively Ready: 1126, 1138, 1152, 1158, 1189, 1192, 1208.
    - Changed the following issues from Open to Tentatively Ready: 987, 999, 1071, 1090, 1108, 1113, 1114.
    - Changed the following issues from Ready to WP: 149, 419, 498, 564, 565, 630, 659, 696, 711, 716, 723, 788, 822, 838, 847, 857, 859, 876, 881, 883, 886, 934, 1004, 1178.
    - Changed the following issues from Tentatively Ready to WP: 1012, 1019.
- R67: 2009-09-25 pre-Santa Cruz mailing.
  - Summary:
    - 282 open issues, up by 32.
    - 935 closed issues, down by 1.
    - 1217 issues total, up by 31.
  - Details:
    - Added the following New issues: 1187, 1188, 1189, 1190, 1191, 1192, 1193, 1194, 1195, 1196, 1197, 1198, 1199, 1200, 1201, 1202, 1203, 1204, 1205, 1206, 1207, 1208, 1209, 1210, 1211, 1212, 1213, 1214, 1215, 1216, 1217.
    - Changed the following issues from NAD to Open: 296.
    - Changed the following issues from WP to Pending WP: 970.
    - Changed the following issues from Open to Review: 976, 1052.
    - Changed the following issues from Ready to Review: 780.
- R66: 2009-07-31 post-Frankfurt mailing.
  - Summary:
    - 250 open issues, down by 128.
    - 936 closed issues, up by 171.
    - 1186 issues total, up by 43.
  - Details:
    - Added the following NAD issues: 1164.
    - Added the following NAD Concepts issues: 1149, 1167.
    - Added the following NAD Editorial issues: 1168.
    - Added the following New issues: 1144, 1145, 1146, 1147, 1148, 1150, 1151, 1152, 1153, 1154, 1155, 1156, 1158, 1159, 1166, 1169, 1170, 1171, 1172, 1173, 1174, 1175, 1176, 1177, 1179, 1180, 1181, 1182, 1183, 1184, 1185, 1186.
    - Added the following Open issues: 1160, 1161, 1162, 1163, 1165.
    - Added the following Ready issues: 1178.
    - Added the following Review issues: 1157.
    - Changed the following issues from Open to Dup: 750, 895.
    - Changed the following issues from Open to NAD: 111, 128, 138, 190, 219, 290, 309, 342, 343, 382, 394, 398, 417, 418, 421, 459, 466, 492, 502, 503, 546, 573, 582, 585, 597, 606, 614, 632, 721, 747, 751, 833, 941, 992.
    - Changed the following issues from Review to NAD: 1003.
    - Changed the following issues from Tentatively NAD to NAD: 568, 644, 667, 669, 701, 702, 785, 863, 901, 903, 946, 988, 995.
    - Changed the following issues from Tentatively Ready to NAD: 1002.
    - Changed the following issues from New to NAD Concepts: 1124, 1127, 1128, 1139, 1140, 1141, 1142, 1143.
    - Changed the following issues from Open to NAD Concepts: 902, 989, 1000, 1007, 1010, 1015, 1016, 1017, 1018, 1026, 1027, 1028, 1029, 1032, 1036, 1057, 1059, 1072, 1078, 1081, 1082, 1083, 1084, 1085, 1086, 1092, 1096, 1105.
    - Changed the following issues from Review to NAD Concepts: 1001, 1005, 1080, 1087, 1111.
    - Changed the following issues from Tentatively NAD to NAD Concepts: 912, 918, 1074.
    - Changed the following issues from Tentatively NAD Editorial to NAD Concepts: 927, 1109.
    - Changed the following issues from Tentatively Ready to NAD Concepts: 906, 913, 914, 928, 1024, 1063, 1067.
    - Changed the following issues from Open to NAD Editorial: 718, 873.
    - Changed the following issues from Tentatively NAD Editorial to NAD Editorial: 424, 825, 830, 837, 862, 867, 884, 945, 952, 969, 972, 973, 979, 1023, 1058, 1060, 1061, 1077, 1101.
    - Changed the following issues from Tentatively Ready to NAD Editorial: 1013, 1107.
    - Changed the following issues from Open to NAD Future: 255, 423, 523, 708, 760, 839, 877.
    - Changed the following issues from CD1 to Open: 823.
    - Changed the following issues from NAD Editorial to Open: 299, 484, 532, 556, 594, 631, 676, 704, 724, 742, 811, 870, 872.
    - Changed the following issues from Review to Open: 879, 919, 929, 939, 987, 1009, 1093.
    - Changed the following issues from Tentatively NAD to Open: 458.
    - Changed the following issues from Tentatively NAD Future to Open: 96.
    - Changed the following issues from Tentatively Ready to Open: 910, 915, 932, 940, 974, 976, 999, 1011.
    - Changed the following issues from Open to Ready: 149, 419, 430, 498, 564, 565, 630, 659, 696, 711, 716, 723, 788, 834, 838, 847, 857, 859, 876, 881, 883, 886, 1004.
    - Changed the following issues from Review to Ready: 780.
    - Changed the following issues from Tentatively NAD to Ready: 822.
    - Changed the following issues from Tentatively Ready to Ready: 934.
    - Changed the following issues from NAD to Review: 871.
    - Changed the following issues from Open to Review: 397, 408, 473, 671, 836, 868, 889, 893, 930, 954, 962, 967, 968.
    - Changed the following issues from Tentatively NAD to Review: 668.
    - Changed the following issues from Tentatively Ready to Review: 950, 1100.
    - Changed the following issues from Open to Tentatively NAD: 588, 617, 625, 971.
    - Changed the following issues from Open to Tentatively NAD Future: 1031, 1062.
    - Changed the following issues from Open to Tentatively Ready: 1012, 1019.
    - Changed the following issues from Tentatively Ready to WP: 688, 765, 810, 814, 853, 869, 878, 888, 890, 898, 899, 904, 907, 909, 922, 925, 931, 938, 943, 948, 949, 965, 970, 975, 981, 982, 984, 986, 990, 991, 993, 994, 997, 998, 1006, 1014, 1021, 1037, 1038, 1039, 1040, 1044, 1045, 1065, 1066, 1070, 1073, 1103.
- R65: 2009-06-19 pre-Frankfurt mailing.
  - Summary:
    - 378 open issues, up by 32.
    - 765 closed issues, up by 0.
    - 1143 issues total, up by 32.
  - Details:
    - Added the following New issues: 1115, 1116, 1117, 1118, 1119, 1120, 1121, 1122, 1123, 1124, 1125, 1126, 1127, 1128, 1129, 1130, 1131, 1132, 1133, 1134, 1135, 1136, 1137, 1138, 1139, 1140, 1141, 1142, 1143.
    - Added the following Open issues: 1112, 1113, 1114.
    - Changed the following issues from Pending NAD Editorial to NAD Editorial: 937.
    - Changed the following issues from New to Open: 696, 716, 727, 865, 900, 911, 916, 917, 920, 933, 935, 941, 947, 951, 953, 954, 955, 956, 977, 978, 985, 989, 996, 1033, 1054, 1056, 1057, 1059, 1062, 1068, 1069, 1071, 1072, 1076, 1090, 1092, 1096, 1098, 1099, 1105, 1106, 1108, 1110.
    - Changed the following issues from Review to Open: 817, 971, 992, 1004, 1010, 1012, 1015, 1019.
    - Changed the following issues from New to Review: 780, 835, 897, 919, 939, 957, 983, 1001, 1080, 1091, 1093, 1094, 1095, 1097, 1102, 1104, 1111.
    - Changed the following issues from Open to Review: 921, 987, 1087.
    - Changed the following issues from New to Tentatively NAD: 568, 701, 702, 785, 863, 903, 912, 918, 946, 995, 1074.
    - Changed the following issues from Open to Tentatively NAD: 458, 644, 667, 668, 669.
    - Changed the following issues from Review to Tentatively NAD: 901.
    - Changed the following issues from Tentatively Ready to Tentatively NAD: 822, 988.
    - Changed the following issues from New to Tentatively NAD Editorial: 837, 862, 867, 927, 945, 952, 969, 972, 973, 979, 1058, 1060, 1061, 1077, 1101, 1109.
    - Changed the following issues from Open to Tentatively NAD Editorial: 424, 825, 830, 884.
    - Changed the following issues from Review to Tentatively NAD Editorial: 1023.
    - Changed the following issues from Open to Tentatively NAD Future: 96.
    - Changed the following issues from New to Tentatively Ready: 810, 898, 906, 910, 913, 914, 915, 925, 974, 976, 981, 982, 984, 990, 998, 999, 1063, 1067, 1070, 1073, 1100, 1103, 1107.
    - Changed the following issues from Open to Tentatively Ready: 688, 814.
    - Changed the following issues from Review to Tentatively Ready: 899, 907, 909, 934, 938, 940, 943, 950, 965, 970, 975, 986, 991, 993, 994, 997, 1002, 1006, 1011, 1013, 1014, 1021, 1024, 1037, 1038, 1039, 1040, 1044, 1045, 1065, 1066.
- R64: 2009-05-01 mid-term mailing.
  - Summary:
    - 346 open issues, up by 19.
    - 765 closed issues, up by 0.
    - 1111 issues total, up by 19.
  - Details:
    - Added the following New issues: 1093, 1094, 1095, 1096, 1097, 1098, 1099, 1100, 1101, 1102, 1103, 1104, 1105, 1106, 1107, 1108, 1109, 1110, 1111.
    - Changed the following issues from DR to CD1: 130, 386, 406, 409, 413, 434, 438, 444, 445, 455, 457, 460, 469, 533.
    - Changed the following issues from Review to New: 1070.
- R63: 2009-03-20 post-Summit mailing.
  - Summary:
    - 327 open issues, up by 96.
    - 765 closed issues, up by 14.
    - 1092 issues total, up by 110.
  - Details:
    - Added the following NAD Editorial issues: 1022.
    - Added the following NAD Future issues: 1025.
    - Added the following New issues: 983, 984, 985, 989, 990, 995, 996, 998, 999, 1001, 1033, 1054, 1056, 1057, 1058, 1059, 1060, 1061, 1062, 1063, 1067, 1068, 1069, 1071, 1072, 1073, 1074, 1076, 1077, 1080, 1090, 1091, 1092.
    - Added the following Open issues: 987, 1000, 1007, 1008, 1016, 1017, 1018, 1020, 1026, 1027, 1028, 1029, 1030, 1031, 1032, 1034, 1035, 1036, 1041, 1042, 1046, 1048, 1051, 1052, 1053, 1055, 1064, 1075, 1078, 1079, 1081, 1082, 1083, 1084, 1085, 1086, 1087, 1088, 1089.
    - Added the following Review issues: 986, 991, 992, 993, 994, 997, 1002, 1003, 1004, 1005, 1006, 1009, 1010, 1011, 1012, 1013, 1014, 1015, 1019, 1021, 1023, 1024, 1037, 1038, 1039, 1040, 1043, 1044, 1045, 1047, 1049, 1050, 1065, 1066, 1070.
    - Added the following Tentatively Ready issues: 988.
    - Changed the following issues from New to Dup: 905, 942.
    - Changed the following issues from New to NAD: 980.
    - Changed the following issues from New to NAD Editorial: 874, 875.
    - Changed the following issues from Open to NAD Editorial: 732, 793, 794, 800.
    - Changed the following issues from Pending NAD Editorial to NAD Editorial: 683, 892.
    - Changed the following issues from Ready to NAD Editorial: 803.
    - Changed the following issues from NAD to Open: 466.
    - Changed the following issues from NAD Future to Open: 111, 138, 149, 219.
    - Changed the following issues from New to Open: 880, 891, 893, 902, 908, 921, 923, 924, 926, 930, 936, 944, 958, 959, 960, 961, 962, 963, 964, 966, 967, 968.
    - Changed the following issues from Ready to Open: 788.
    - Changed the following issues from New to Pending NAD Editorial: 937.
    - Changed the following issues from New to Review: 879, 899, 901, 907, 909, 929, 934, 938, 940, 943, 950, 965, 970, 971, 975.
    - Changed the following issues from Open to Review: 817.
    - Changed the following issues from New to Tentatively Ready: 904, 922, 928, 931, 932, 948, 949.
    - Changed the following issues from Open to Tentatively Ready: 890.
    - Changed the following issues from Review to Tentatively Ready: 765, 822, 853, 869, 878, 888.
    - Changed the following issues from Ready to WP: 752, 753, 758, 821, 866, 894.
- R62: 2009-02-06 pre-Summit mailing.
  - Summary:
    - 231 open issues, up by 44.
    - 751 closed issues, up by 0.
    - 982 issues total, up by 44.
  - Details:
    - Added the following New issues: 939, 940, 941, 942, 943, 944, 945, 946, 947, 948, 949, 950, 951, 952, 953, 954, 955, 956, 957, 958, 959, 960, 961, 962, 963, 964, 965, 966, 967, 968, 969, 970, 971, 972, 973, 974, 975, 976, 977, 978, 979, 980, 981, 982.
- R61: 2008-12-05 mid-term mailing.
  - Summary:
    - 187 open issues, up by 20.
    - 751 closed issues, up by 0.
    - 938 issues total, up by 20.
  - Details:
    - Added the following New issues: 919, 920, 921, 922, 923, 924, 925, 926, 927, 928, 929, 930, 931, 932, 933, 934, 935, 936, 937, 938.
- R60: 2008-10-03 post-San Francisco mailing.
  - Summary:
    - 167 open issues, down by 25.
    - 751 closed issues, up by 65.
    - 918 issues total, up by 40.
  - Details:
    - Added the following CD1 issues: 882.
    - Added the following New issues: 879, 880, 891, 893, 897, 898, 899, 900, 901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911, 912, 913, 914, 915, 916, 917, 918.
    - Added the following Open issues: 881, 883, 884, 885, 886, 887, 889, 890, 895, 896.
    - Added the following Pending NAD Editorial issues: 892.
    - Added the following Ready issues: 894.
    - Added the following Review issues: 888.
    - Changed the following issues from New to CD1: 818, 820, 843, 845, 846, 856, 858.
    - Changed the following issues from Ready to CD1: 180, 387, 396, 522, 629, 691, 713, 714, 720, 728, 762, 769, 771, 772, 776, 779, 787, 805, 806, 807, 808, 809, 813, 824, 829, 842, 844, 848, 850, 852.
    - Changed the following issues from Review to CD1: 23, 675, 692, 698, 709, 734, 804, 823.
    - Changed the following issues from WP to CD1: 44, 49, 76, 91, 92, 98, 103, 109, 117, 118, 120, 123, 136, 153, 165, 167, 171, 179, 182, 183, 184, 185, 186, 187, 198, 200, 201, 202, 206, 214, 221, 225, 226, 228, 229, 230, 231, 232, 233, 234, 235, 237, 238, 239, 240, 241, 242, 243, 247, 248, 250, 251, 252, 253, 254, 256, 258, 259, 260, 261, 262, 263, 264, 265, 266, 268, 270, 271, 272, 273, 274, 275, 276, 278, 280, 281, 282, 283, 284, 285, 286, 288, 291, 292, 294, 295, 297, 298, 300, 301, 303, 305, 306, 307, 308, 310, 311, 312, 315, 316, 317, 318, 319, 320, 321, 322, 324, 325, 327, 328, 329, 331, 333, 334, 335, 336, 337, 338, 339, 340, 341, 345, 346, 347, 349, 352, 354, 355, 358, 359, 360, 362, 363, 364, 365, 369, 370, 371, 373, 375, 376, 379, 380, 381, 383, 384, 389, 391, 395, 400, 401, 402, 403, 404, 405, 407, 410, 411, 412, 414, 415, 416, 420, 422, 425, 426, 428, 432, 435, 436, 441, 442, 443, 448, 449, 453, 456, 461, 464, 465, 467, 468, 474, 475, 478, 488, 495, 496, 497, 505, 507, 508, 518, 519, 520, 521, 524, 527, 530, 531, 534, 535, 537, 538, 540, 541, 542, 543, 545, 550, 551, 552, 559, 561, 562, 563, 566, 567, 574, 575, 576, 577, 578, 581, 586, 589, 593, 595, 596, 607, 608, 609, 610, 611, 612, 613, 616, 618, 619, 620, 621, 622, 623, 624, 628, 634, 638, 640, 643, 646, 650, 651, 652, 654, 655, 660, 661, 664, 665, 666, 672, 673, 674, 677, 678, 679, 680, 681, 682, 685, 687, 689, 693, 694, 695, 699, 700, 703, 705, 706, 710, 712, 715, 722, 740, 743, 744, 746, 749, 755, 759, 761, 766, 768, 770, 775, 777, 778, 781, 782, 783, 789, 792, 798.
    - Changed the following issues from Open to Dup: 670.
    - Changed the following issues from New to NAD: 849, 855, 871.
    - Changed the following issues from Open to NAD: 454, 832.
    - Changed the following issues from New to NAD Editorial: 811, 812, 841, 864, 870, 872.
    - Changed the following issues from Open to NAD Editorial: 299, 484, 556, 631, 676, 704, 724, 742.
    - Changed the following issues from Pending NAD Editorial to NAD Editorial: 532, 594, 717, 725, 738.
    - Changed the following issues from New to Open: 721, 751, 814, 816, 817, 819, 827, 836, 838, 847, 857, 859, 860, 861, 868, 873, 876, 877.
    - Changed the following issues from Pending NAD Editorial to Open: 424, 625.
    - Changed the following issues from Review to Open: 851.
    - Changed the following issues from New to Ready: 788, 821, 866.
    - Changed the following issues from Open to Ready: 753.
    - Changed the following issues from Review to Ready: 752, 758, 803.
    - Changed the following issues from New to Review: 765, 822, 853, 854, 869, 878.
    - Changed the following issues from TC to TC1: 1, 3, 5, 7, 8, 9, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 59, 60, 61, 62, 63, 64, 66, 68, 69, 70, 71, 74, 75, 78, 79, 80, 83, 86, 90, 106, 108, 110, 112, 114, 115, 119, 122, 124, 125, 126, 127, 129, 132, 133, 134, 137, 139, 141, 142, 144, 146, 147, 148, 150, 151, 152, 154, 155, 156, 158, 159, 160, 161, 164, 168, 169, 170, 172, 173, 174, 175, 176, 181, 189, 193, 195, 199, 208, 209, 210, 211, 212, 217, 220, 222, 223, 224, 227.
- R59: 2008-08-22 pre-San Francisco mailing.
  - Summary:
    - 192 open issues, up by 9.
    - 686 closed issues, up by 0.
    - 878 issues total, up by 9.
  - Details:
    - Added the following New issues: 870, 871, 872, 873, 874, 875, 876, 877, 878.
- R58: 2008-07-28 mid-term mailing.
  - Summary:
    - 183 open issues, up by 12.
    - 686 closed issues, down by 4.
    - 869 issues total, up by 8.
  - Details:
    - Added the following New issues: 862, 863, 864, 865, 866, 867, 868, 869.
    - Changed the following issues from Pending NAD Editorial to NAD Editorial: 393, 557, 592, 754, 757.
    - Changed the following issues from Pending WP to Open: 644.
    - Changed the following issues from WP to Ready: 387, 629.
    - Changed the following issues from Pending NAD Editorial to Review: 709.
- R57: 2008-06-27 post-Sophia Antipolis mailing.
  - Summary:
    - 171 open issues, down by 20.
    - 690 closed issues, up by 43.
    - 861 issues total, up by 23.
  - Details:
    - Added the following NAD issues: 840.
    - Added the following New issues: 841, 843, 845, 846, 847, 849, 853, 854, 855, 856, 857, 858, 859, 860, 861.
    - Added the following Open issues: 839.
    - Added the following Ready issues: 842, 844, 848, 850, 852.
    - Added the following Review issues: 851.
    - Changed the following issues from New to NAD: 826.
    - Changed the following issues from Open to NAD: 570.
    - Changed the following issues from New to NAD Editorial: 786, 831.
    - Changed the following issues from Open to NAD Editorial: 756, 767.
    - Changed the following issues from New to Open: 723, 726, 794, 815, 825, 830, 833, 834.
    - Changed the following issues from Ready to Open: 471.
    - Changed the following issues from Review to Open: 539, 711.
    - Changed the following issues from New to Ready: 713, 714, 769, 772, 779, 787, 805, 806, 807, 808, 809, 813, 824, 829.
    - Changed the following issues from Open to Ready: 180, 396, 522, 720, 762.
    - Changed the following issues from Review to Ready: 691, 728, 771, 776.
    - Changed the following issues from New to Review: 692, 698, 752, 804, 823, 828, 832.
    - Changed the following issues from Open to Review: 23, 675, 734, 803.
    - Changed the following issues from Ready to Review: 758.
    - Changed the following issues from Ready to WP: 387, 518, 550, 574, 595, 596, 612, 618, 629, 638, 672, 673, 685, 710, 715, 722, 740, 743, 744, 746, 749, 755, 759, 761, 766, 768, 770, 775, 777, 778, 781, 782, 783, 789, 792, 798.
- R56: 2008-05-16 pre-Sophia Antipolis mailing.
  - Summary:
    - 191 open issues, up by 24.
    - 647 closed issues, up by 1.
    - 838 issues total, up by 25.
  - Details:
    - Added the following New issues: 814, 815, 816, 817, 818, 819, 820, 821, 822, 823, 824, 825, 826, 827, 828, 829, 830, 831, 832, 833, 834, 835, 836, 837, 838.
    - Changed the following issues from New to NAD: 802.
- R55: 2008-03-14 post-Bellevue mailing.
  - Summary:
    - 167 open issues, down by 39.
    - 646 closed issues, up by 65.
    - 813 issues total, up by 26.
  - Details:
    - Added the following Dup issues: 795.
    - Added the following NAD issues: 790, 791, 796, 797, 799.
    - Added the following New issues: 788, 794, 802, 804, 805, 806, 807, 808, 809, 810, 811, 812, 813.
    - Added the following Open issues: 793, 800, 801, 803.
    - Added the following Ready issues: 789, 792, 798.
    - Changed the following issues from NAD Future to Dup: 116.
    - Changed the following issues from NAD Future to NAD: 188, 323.
    - Changed the following issues from New to NAD: 729, 730, 731, 733, 735, 736, 737, 739, 741, 745, 748, 763, 764, 773, 784.
    - Changed the following issues from Open to NAD: 388, 462, 579, 627, 653, 686, 707.
    - Changed the following issues from NAD Future to NAD Editorial: 140, 390.
    - Changed the following issues from Open to NAD Editorial: 529, 626.
    - Changed the following issues from Review to NAD Editorial: 645, 684.
    - Changed the following issues from NAD Future to Open: 128, 180, 190.
    - Changed the following issues from New to Open: 617, 718, 719, 720, 724, 732, 734, 742, 747, 750, 753, 756, 760, 762, 767, 774.
    - Changed the following issues from Ready to Open: 675, 676, 688.
    - Changed the following issues from New to Pending NAD Editorial: 709, 717, 725, 738, 754, 757.
    - Changed the following issues from Open to Pending NAD Editorial: 424, 557, 625.
    - Changed the following issues from New to Ready: 710, 715, 722, 740, 743, 744, 746, 749, 755, 758, 759, 761, 766, 768, 770, 775, 777, 778, 781, 782, 783.
    - Changed the following issues from Open to Ready: 387, 471, 550, 612, 629, 673.
    - Changed the following issues from Review to Ready: 518, 574, 596, 618, 638, 672, 685.
    - Changed the following issues from New to Review: 711, 728, 771, 776.
    - Changed the following issues from Open to Review: 539.
    - Changed the following issues from Ready to WP: 561, 562, 563, 567, 581, 620, 621, 622, 623, 624, 661, 664, 665, 666, 674, 679, 680, 687, 689, 693, 694, 695, 700, 703, 705, 706.
    - Changed the following issues from Tentatively Ready to WP: 527.
- R54: 2008-02-01 pre-Bellevue mailing.
  - Summary:
    - 206 open issues, up by 23.
    - 581 closed issues, up by 0.
    - 787 issues total, up by 23.
  - Details:
    - Added the following New issues: 765, 766, 767, 768, 769, 770, 771, 772, 773, 774, 775, 776, 777, 778, 779, 780, 781, 782, 783, 784, 785, 786, 787.
    - Changed the following issues from NAD Future to Dup: 105, 348.
    - Changed the following issues from NAD Future to NAD Editorial: 353.
    - Changed the following issues from New to NAD Editorial: 697.
    - Changed the following issues from NAD Future to Open: 388.
    - Changed the following issues from Open to Tentatively Ready: 527.
- R53: 2007-12-09 mid-term mailing.
  - Summary:
    - 183 open issues, up by 11.
    - 581 closed issues, down by 1.
    - 764 issues total, up by 10.
  - Details:
    - Added the following New issues: 755, 756, 757, 758, 759, 760, 761, 762, 763, 764.
    - Changed the following issues from NAD to Open: 463.
    - Changed the following issues from Pending WP to WP: 607, 608, 654, 655, 677, 682.
- R52: 2007-10-19 post-Kona mailing.
  - Summary:
    - 172 open issues, up by 4.
    - 582 closed issues, up by 27.
    - 754 issues total, up by 31.
  - Details:
    - Added the following New issues: 724, 725, 726, 727, 728, 729, 730, 731, 732, 733, 734, 735, 736, 737, 738, 739, 740, 741, 742, 743, 744, 745, 746, 747, 748, 749, 750, 751, 752, 753, 754.
    - Changed the following issues from NAD Future to Dup: 77, 350.
    - Changed the following issues from New to NAD: 639, 657, 663.
    - Changed the following issues from Open to NAD: 548.
    - Changed the following issues from New to Open: 546, 550, 564, 565, 573, 585, 588, 627, 629, 630, 632, 635, 653, 659, 667, 668, 669, 670, 671, 673, 686, 704, 707, 708.
    - Changed the following issues from New to Pending NAD Editorial: 393, 592.
    - Changed the following issues from New to Pending WP: 607, 608, 654, 655, 677, 682.
    - Changed the following issues from New to Ready: 561, 562, 563, 567, 581, 595, 620, 621, 622, 623, 624, 661, 664, 665, 666, 674, 675, 676, 679, 687, 688, 689, 693, 694, 695, 700, 703, 705, 706.
    - Changed the following issues from Open to Ready: 680.
    - Changed the following issues from New to Review: 574, 596, 618, 638, 645, 672, 684, 685, 691.
    - Changed the following issues from New to WP: 552, 634, 650, 651, 652, 678, 681, 699, 712.
    - Changed the following issues from Open to WP: 258, 401, 524.
    - Changed the following issues from Ready to WP: 488, 577, 660.
- R51: 2007-09-09 pre-Kona mailing.
  - Summary:
    - 168 open issues, up by 15.
    - 555 closed issues, up by 0.
    - 723 issues total, up by 15.
  - Details:
    - Added the following New issues: 709, 710, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 721, 722, 723.
- R50: 2007-08-05 post-Toronto mailing.
  - Summary:
    - 153 open issues, down by 5.
    - 555 closed issues, up by 17.
    - 708 issues total, up by 12.
  - Details:
    - Added the following New issues: 697, 698, 699, 700, 701, 702, 703, 704, 705, 706, 707, 708.
    - Changed the following issues from New to NAD: 583, 584, 662.
    - Changed the following issues from Open to NAD: 528.
    - Changed the following issues from New to NAD Editorial: 637, 647, 658, 690.
    - Changed the following issues from Open to NAD Editorial: 525.
    - Changed the following issues from Pending NAD Editorial to NAD Editorial: 553, 571, 591, 633, 636, 641, 642, 648, 649, 656.
    - Changed the following issues from New to Open: 579, 631, 680.
    - Changed the following issues from Pending WP to Open: 258.
    - Changed the following issues from Ready to Pending WP: 644.
    - Changed the following issues from New to Ready: 577, 660.
    - Changed the following issues from Open to Ready: 488.
    - Changed the following issues from Open to Review: 518.
    - Changed the following issues from Ready to TRDec: 604.
    - Changed the following issues from DR to WP: 453.
    - Changed the following issues from Ready to WP: 531, 551, 566, 628, 640, 643, 646.
- R49: 2007-06-23 pre-Toronto mailing.
  - Summary:
    - 158 open issues, up by 13.
    - 538 closed issues, up by 7.
    - 696 issues total, up by 20.
  - Details:
    - Added the following New issues: 677, 678, 679, 680, 681, 682, 684, 685, 686, 687, 688, 689, 690, 691, 692, 693, 694, 695, 696.
    - Added the following Pending NAD Editorial issues: 683.
    - Changed the following issues from New to NAD Editorial: 587.
    - Changed the following issues from Open to NAD Editorial: 590.
    - Changed the following issues from New to Pending NAD Editorial: 636, 642, 648, 649.
- R48: 2007-05-06 post-Oxford mailing.
  - Summary:
    - 145 open issues, down by 33.
    - 531 closed issues, up by 53.
    - 676 issues total, up by 20.
  - Details:
    - Added the following New issues: 657, 658, 659, 660, 661, 662, 663, 664, 665, 666, 667, 668, 669, 670, 671, 672, 673, 674, 675, 676.
    - Changed the following issues from Tentatively Ready to Dup: 479, 536.
    - Changed the following issues from Tentatively Ready to NAD: 385, 463, 466, 470, 515, 526, 547, 560, 572.
    - Changed the following issues from NAD to NAD Editorial: 351, 357, 368, 499, 504, 512, 513, 514, 516, 544, 549, 555, 558.
    - Changed the following issues from Tentatively Ready to NAD Editorial: 482, 615.
    - Changed the following issues from NAD_Future to NAD Future: 77, 105, 111, 116, 128, 138, 140, 149, 180, 188, 190, 219, 323, 348, 350, 353, 388, 390.
    - Changed the following issues from Tentatively Ready to Open: 471.
    - Changed the following issues from New to Pending NAD Editorial: 633, 641, 656.
    - Changed the following issues from Tentatively Ready to Pending NAD Editorial: 532, 553, 571, 591, 594.
    - Changed the following issues from Tentatively Ready to Pending WP: 258.
    - Changed the following issues from New to Ready: 566, 628, 640, 643, 644, 646.
    - Changed the following issues from Review to Ready: 531, 551, 604.
    - Changed the following issues from Ready to TRDec: 598, 599, 600, 601, 602, 603, 605.
    - Changed the following issues from Ready to WP: 543, 545.
    - Changed the following issues from Tentatively Ready to WP: 201, 206, 233, 254, 416, 422, 456, 534, 542, 559, 575, 576, 578, 586, 589, 593, 609, 610, 611, 613, 616, 619.
- R47: 2007-03-09 pre-Oxford mailing.
  - Summary:
    - 178 open issues, up by 37.
    - 478 closed issues, up by 0.
    - 656 issues total, up by 37.
  - Details:
    - Added the following New issues: 620, 621, 622, 623, 624, 627, 628, 629, 630, 631, 632, 633, 634, 635, 636, 637, 638, 639, 640, 641, 642, 643, 644, 645, 646, 647, 648, 649, 650, 651, 652, 653, 654, 655, 656.
    - Added the following Open issues: 625, 626.
    - Changed the following issues from New to Open: 570, 580, 582, 590, 612, 614.
    - Changed the following issues from New to Tentatively Ready: 547, 553, 560, 571, 572, 575, 576, 578, 586, 589, 591, 593, 594, 609, 610, 611, 613, 615, 616, 619.
    - Changed the following issues from Open to Tentatively Ready: 201, 206, 233, 254, 258, 385, 416, 422, 456, 463, 466, 470, 471, 479, 482, 515, 526, 532, 536, 542, 559.
    - Changed the following issues from Review to Tentatively Ready: 534.
- R46: 2007-01-12 mid-term mailing.
  - Summary:
    - 141 open issues, up by 11.
    - 478 closed issues, down by 1.
    - 619 issues total, up by 10.
  - Details:
    - Added new issues 610, 611, 612, 613, 614, 615, 616, 617, 618, 619.
- R45: 2006-11-03 post-Portland mailing.
  - Summary:
    - 130 open issues, up by 0.
    - 479 closed issues, up by 17.
    - 609 issues total, up by 17.
  - Details:
    - Moved issues 520, 521, 530, 535, 537, 538, 540, 541 to WP.
    - Moved issues 504, 512, 516, 544, 549, 554, 555, 558 to NAD.
    - Moved issue 569 to Dup.
    - Moved issues 518, 523, 524, 542, 556, 557, 559, 597, 606 to Open.
    - Moved issues 543, 545, 549, 549, 598 - 603, 605 to Ready.
    - Moved issues 531, 551, 604 to Review.
    - Added new issues 593, 594, 595, 596, 597, 598, 599, 600, 601, 602, 603, 604, 605, 606, 607, 608, 609.
- R44: 2006-09-08 pre-Portland mailing.
  - Summary:
    - 130 open issues, up by 6.
    - 462 closed issues, down by 1.
    - 592 issues total, up by 5.
  - Details:
    - Added new issues 583, 584, 585, 586, 587, 588, 589, 590, 591, 592.
- R43: 2006-06-23 mid-term mailing.
  - Summary:
    - 124 open issues, up by 14.
    - 463 closed issues, down by 1.
    - 587 issues total, up by 13.
  - Details:
    - Added new issues 575, 576, 577, 578, 579, 580, 581, 582.
    - Reopened 255.
    - Moved issues 520, 541, 544, 569 to Tentatively Ready.
- R42: 2006-04-21 post-Berlin mailing.
  - Summary:
    - 110 open issues, down by 16.
    - 464 closed issues, up by 24.
    - 574 issues total, up by 8.
  - Details:
    - Added new issues 567, 568, 569, 570, 571, 572.
    - Moved issues 499, 501, 506, 509, 510, 511, 513, 514, 517 to NAD.
    - Moved issues 502, 503, 515, 516, 522, 525, 526, 527, 528, 529, 532, 536, 539, 548 to Open.
    - Moved issue 504, 512, 521, 530, 531, 535, 537, 538, 540, 549 to Ready.
    - Moved issues 247, 294, 362, 369, 371, 376, 384, 475, 478, 495, 497, 505, 507, 508, 519 to WP.
    - Moved issue 534 to Review.
- R41: 2006-02-24 pre-Berlin mailing.
  - Summary:
    - 126 open issues, up by 31.
    - 440 closed issues, up by 0.
    - 566 issues total, up by 31.
  - Details:
    - Added new issues 536, 537, 538, 539, 540, 541, 542, 543, 544, 545, 546, 547, 548, 549, 550 ,551, 552, 553, 554, 555, 556, 557, 558, 559, 560, 561, 562, 563, 564, 565, 566.
    - Moved 342 from Ready to Open.
    - Reopened 309.
- R40: 2005-12-16 mid-term mailing.
  - Summary:
    - 95 open issues.
    - 440 closed issues.
    - 535 issues total.
  - Details:
    - Added new issues 529, 530, 531, 532, 533, 534, 535.
- R39: 2005-10-14 post-Mont Tremblant mailing. Added new issues 526-528. Moved issues 280, 461, 464, 465, 467, 468, 474, 496 from Ready to WP as per the vote from Mont Tremblant. Moved issues 247, 294, 342, 362, 369, 371, 376, 384, 475, 478, 495, 497 from Review to Ready. Moved issues 498, 504, 506, 509, 510, 511, 512, 513, 514 from New to Open. Moved issues 505, 507, 508, 519 from New to Ready. Moved issue 500 from New to NAD. Moved issue 518 from New to Review.
- R38: 2005-07-03 pre-Mont Tremblant mailing. Merged open TR1 issues in 504-522. Added new issues 523-523
- R37: 2005-06 mid-term mailing. Added new issues 498-503.
- R36: 2005-04 post-Lillehammer mailing. All issues in "ready" status except for 454 were moved to "DR" status, and all issues previously in "DR" status were moved to "WP".
- R35: 2005-03 pre-Lillehammer mailing.
- R34: 2005-01 mid-term mailing. Added new issues 488-494.
- R33: 2004-11 post-Redmond mailing. Reflects actions taken in Redmond.
- R32: 2004-09 pre-Redmond mailing: reflects new proposed resolutions and new issues received after the 2004-07 mailing. Added new issues 479-481.
- R31: 2004-07 mid-term mailing: reflects new proposed resolutions and new issues received after the post-Sydney mailing. Added new issues 463-478.
- R30: Post-Sydney mailing: reflects decisions made at the Sydney meeting. Voted all "Ready" issues from R29 into the working paper. Added new issues 460-462.
- R29: Pre-Sydney mailing. Added new issues 441-457.
- R28: Post-Kona mailing: reflects decisions made at the Kona meeting. Added new issues 432-440.
- R27: Pre-Kona mailing. Added new issues 404-431.
- R26: Post-Oxford mailing: reflects decisions made at the Oxford meeting. All issues in Ready status were voted into DR status. All issues in DR status were voted into WP status.
- R25: Pre-Oxford mailing. Added new issues 390-402.
- R24: Post-Santa Cruz mailing: reflects decisions made at the Santa Cruz meeting. All Ready issues from R23 with the exception of 253, which has been given a new proposed resolution, were moved to DR status. Added new issues 383-389. (Issues 387-389 were discussed at the meeting.) Made progress on issues 225, 226, 229: 225 and 229 have been moved to Ready status, and the only remaining concerns with 226 involve wording.
- R23: Pre-Santa Cruz mailing. Added new issues 367-382. Moved issues in the TC to TC status.
- R22: Post-Curaçao mailing. Added new issues 362-366.
- R21: Pre-Curaçao mailing. Added new issues 351-361.
- R20: Post-Redmond mailing; reflects actions taken in Redmond. Added new issues 336-350, of which issues 347-350 were added since Redmond, hence not discussed at the meeting. All Ready issues were moved to DR status, with the exception of issues 284, 241, and 267. Noteworthy issues discussed at Redmond include 120 202, 226, 233, 270, 253, 254, 323.
- R19: Pre-Redmond mailing. Added new issues 323-335.
- R18: Post-Copenhagen mailing; reflects actions taken in Copenhagen. Added new issues 312-317, and discussed new issues 271-314. Changed status of issues 103 118 136 153 165 171 183 184 185 186 214 221 234 237 243 248 251 252 256 260 261 262 263 265 268 to DR. Changed status of issues 49 109 117 182 228 230 232 235 238 241 242 250 259 264 266 267 271 272 273 275 281 284 285 286 288 292 295 297 298 301 303 306 307 308 312 to Ready. Closed issues 111 277 279 287 289 293 302 313 314 as NAD.
- R17: Pre-Copenhagen mailing. Converted issues list to XML. Added proposed resolutions for issues 49, 76, 91, 235, 250, 267. Added new issues 278-311.
- R16: post-Toronto mailing; reflects actions taken in Toronto. Added new issues 265-277. Changed status of issues 3, 8, 9, 19, 26, 31, 61, 63, 86, 108, 112, 114, 115, 122, 127, 129, 134, 137, 142, 144, 146, 147, 159, 164, 170, 181, 199, 208, 209, 210, 211, 212, 217, 220, 222, 223, 224, 227 to "DR". Reopened issue 23. Reopened issue 187. Changed issues 2 and 4 to NAD. Fixed a typo in issue 17. Fixed issue 70: signature should be changed both places it appears. Fixed issue 160: previous version didn't fix the bug in enough places.
- R15: pre-Toronto mailing. Added issues 233-264. Some small HTML formatting changes so that we pass Weblint tests.
- R14: post-Tokyo II mailing; reflects committee actions taken in Tokyo. Added issues 228 to 232. (00-0019R1/N1242)
- R13: pre-Tokyo II updated: Added issues 212 to 227.
- R12: pre-Tokyo II mailing: Added issues 199 to 211. Added "and paragraph 5" to the proposed resolution of issue 29. Add further rationale to issue 178.
- R11: post-Kona mailing: Updated to reflect LWG and full committee actions in Kona (99-0048/N1224). Note changed resolution of issues 4 and 38. Added issues 196 to 198. Closed issues list split into "defects" and "closed" documents. Changed the proposed resolution of issue 4 to NAD, and changed the wording of proposed resolution of issue 38.
- R10: pre-Kona updated. Added proposed resolutions 83, 86, 91, 92, 109. Added issues 190 to 195. (99-0033/D1209, 14 Oct 99)
- R9: pre-Kona mailing. Added issues 140 to 189. Issues list split into separate "active" and "closed" documents. (99-0030/N1206, 25 Aug 99)
- R8: post-Dublin mailing. Updated to reflect LWG and full committee actions in Dublin. (99-0016/N1193, 21 Apr 99)
- R7: pre-Dublin updated: Added issues 130, 131, 132, 133, 134, 135, 136, 137, 138, 139 (31 Mar 99)
- R6: pre-Dublin mailing. Added issues 127, 128, and 129. (99-0007/N1194, 22 Feb 99)
- R5: update issues 103, 112; added issues 114 to 126. Format revisions to prepare for making list public. (30 Dec 98)
- R4: post-Santa Cruz II updated: Issues 110, 111, 112, 113 added, several issues corrected. (22 Oct 98)
- R3: post-Santa Cruz II: Issues 94 to 109 added, many issues updated to reflect LWG consensus (12 Oct 98)
- R2: pre-Santa Cruz II: Issues 73 to 93 added, issue 17 updated. (29 Sep 98)
- R1: Correction to issue 55 resolution, 60 code format, 64 title. (17 Sep 98)

## Defect Reports

### 1. C library linkage editing oversight

Section: 17.6.2.3 [using.linkage] Status: TC1 Submitter: Beman Dawes Opened: 1997-11-16 Last modified: 2008-09-26

View all issues with TC1 status.

Discussion:

The change specified in the proposed resolution below did not make it into the Standard. This change was accepted in principle at the London meeting, and the exact wording below was accepted at the Morristown meeting.

Proposed resolution:

Change 17.6.2.3 [using.linkage] paragraph 2 from:

> It is unspecified whether a name from the Standard C library declared with external linkage has either extern "C" or extern "C++" linkage.

to:

> Whether a name from the Standard C library declared with external linkage has extern "C" or extern "C++" linkage is implementation defined. It is recommended that an implementation use extern "C++" linkage for this purpose.

### 3. Atexit registration during atexit() call is not described

Section: 18.5 [support.start.term] Status: TC1 Submitter: Steve Clamage Opened: 1997-12-12 Last modified: 2008-09-26

View all other issues in [support.start.term].

View all issues with TC1 status.

Discussion:

We appear not to have covered all the possibilities of exit processing with respect to atexit registration.
Example 1: (C and C++)

        #include <stdlib.h>
        void f1() { }
        void f2() { atexit(f1); }

        int main()
        {
            atexit(f2); // the only use of f2
            return 0; // for C compatibility
        }

At program exit, f2 gets called due to its registration in main. Running f2 causes f1 to be newly registered during the exit processing. Is this a valid program? If so, what are its semantics?

Interestingly, neither the C standard, nor the C++ draft standard nor the forthcoming C9X Committee Draft says directly whether you can register a function with atexit during exit processing.

All 3 standards say that functions are run in reverse order of their registration. Since f1 is registered last, it ought to be run first, but by the time it is registered, it is too late to be first.

If the program is valid, the standards are self-contradictory about its semantics.

Example 2: (C++ only)

        void F() { static T t; } // type T has a destructor

        int main()
        {
            atexit(F); // the only use of F
        }

Function F registered with atexit has a local static variable t, and F is called for the first time during exit processing. A local static object is initialized the first time control flow passes through its definition, and all static objects are destroyed during exit processing. Is the code valid? If so, what are its semantics?

Section 18.3 "Start and termination" says that if a function F is registered with atexit before a static object t is initialized, F will not be called until after t's destructor completes.

In example 2, function F is registered with atexit before its local static object O could possibly be initialized. On that basis, it must not be called by exit processing until after O's destructor completes. But the destructor cannot be run until after F is called, since otherwise the object could not be constructed in the first place.

If the program is valid, the standard is self-contradictory about its semantics.

I plan to submit Example 1 as a public comment on the C9X CD, with a recommendation that the results be undefined. (Alternative: make it unspecified. I don't think it is worthwhile to specify the case where f1 itself registers additional functions, each of which registers still more functions.)

I think we should resolve the situation in the whatever way the C committee decides.

For Example 2, I recommend we declare the results undefined.

[See reflector message lib-6500 for further discussion.]

Proposed resolution:

Change section 18.3/8 from:

> First, objects with static storage duration are destroyed and functions registered by calling atexit are called. Objects with static storage duration are destroyed in the reverse order of the completion of their constructor. (Automatic objects are not destroyed as a result of calling exit().) Functions registered with atexit are called in the reverse order of their registration. A function registered with atexit before an object obj1 of static storage duration is initialized will not be called until obj1's destruction has completed. A function registered with atexit after an object obj2 of static storage duration is initialized will be called before obj2's destruction starts.

to:

> First, objects with static storage duration are destroyed and functions registered by calling atexit are called. Non-local objects with static storage duration are destroyed in the reverse order of the completion of their constructor. (Automatic objects are not destroyed as a result of calling exit().) Functions registered with atexit are called in the reverse order of their registration, except that a function is called after any previously registered functions that had already been called at the time it was registered. A function registered with atexit before a non-local object obj1 of static storage duration is initialized will not be called until obj1's destruction has completed. A function registered with atexit after a non-local object obj2 of static storage duration is initialized will be called before obj2's destruction starts. A local static object obj3 is destroyed at the same time it would be if a function calling the obj3 destructor were registered with atexit at the completion of the obj3 constructor.

Rationale:

See 99-0039/N1215, October 22, 1999, by Stephen D. Clamage for the analysis supporting to the proposed resolution.

### 5. String::compare specification questionable

Section: 21.4.6.8 [string::swap] Status: TC1 Submitter: Jack Reeves Opened: 1997-12-11 Last modified: 2008-09-26

View all other issues in [string::swap].

View all issues with TC1 status.

Duplicate of: 87

Discussion:

At the very end of the basic_string class definition is the signature: int compare(size_type pos1, size_type n1, const charT* s, size_type n2 = npos) const; In the following text this is defined as: returns basic_string<charT,traits,Allocator>(*this,pos1,n1).compare( basic_string<charT,traits,Allocator>(s,n2);

Since the constructor basic_string(const charT* s, size_type n, const Allocator& a = Allocator()) clearly requires that s != NULL and n < npos and further states that it throws length_error if n == npos, it appears the compare() signature above should always throw length error if invoked like so: str.compare(1, str.size()-1, s); where 's' is some null terminated character array.

This appears to be a typo since the obvious intent is to allow either the call above or something like: str.compare(1, str.size()-1, s, strlen(s)-1);

This would imply that what was really intended was two signatures int compare(size_type pos1, size_type n1, const charT* s) const int compare(size_type pos1, size_type n1, const charT* s, size_type n2) const; each defined in terms of the corresponding constructor.

Proposed resolution:

Replace the compare signature in 21.4 [basic.string] (at the very end of the basic_string synopsis) which reads:

> `int compare(size_type pos1, size_type n1,
> const charT* s, size_type n2 = npos) const;`

with:

> `int compare(size_type pos1, size_type n1,
> const charT* s) const;
> int compare(size_type pos1, size_type n1,
> const charT* s, size_type n2) const;`

Replace the portion of 21.4.6.8 [string::swap] paragraphs 5 and 6 which read:

> `int compare(size_type pos, size_type n1,
> charT * s, size_type n2 = npos) const;
> ` Returns:`
> basic_string<charT,traits,Allocator>(*this, pos, n1).compare(
> basic_string<charT,traits,Allocator>( s, n2))`

with:

> `int compare(size_type pos, size_type n1,
> const charT * s) const;
> ` Returns:`
> basic_string<charT,traits,Allocator>(*this, pos, n1).compare(
> basic_string<charT,traits,Allocator>( s ))
> int compare(size_type pos, size_type n1,
> const charT * s, size_type n2) const;
> ` Returns:`
> basic_string<charT,traits,Allocator>(*this, pos, n1).compare(
> basic_string<charT,traits,Allocator>( s, n2))`

Editors please note that in addition to splitting the signature, the third argument becomes const, matching the existing synopsis.

Rationale:

While the LWG dislikes adding signatures, this is a clear defect in the Standard which must be fixed. The same problem was also identified in issues 7 (item 5) and 87.

### 7. String clause minor problems

Section: 21 [strings] Status: TC1 Submitter: Matt Austern Opened: 1997-12-15 Last modified: 2008-09-26

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Discussion:

(1) In 21.4.6.4 [string::insert], the description of template <class InputIterator> insert(iterator, InputIterator, InputIterator) makes no sense. It refers to a member function that doesn't exist. It also talks about the return value of a void function.

(2) Several versions of basic_string::replace don't appear in the class synopsis.

(3) basic_string::push_back appears in the synopsis, but is never described elsewhere. In the synopsis its argument is const charT, which doesn't makes much sense; it should probably be charT, or possible const charT&.

(4) basic_string::pop_back is missing.

(5) int compare(size_type pos, size_type n1, charT* s, size_type n2 = npos) make no sense. First, it's const charT* in the synopsis and charT* in the description. Second, given what it says in RETURNS, leaving out the final argument will always result in an exception getting thrown. This is paragraphs 5 and 6 of 21.4.6.8 [string::swap]

(6) In table 37, in section 21.2.1 [char.traits.require], there's a note for X::move(s, p, n). It says "Copies correctly even where p is in [s, s+n)". This is correct as far as it goes, but it doesn't go far enough; it should also guarantee that the copy is correct even where s in in [p, p+n). These are two orthogonal guarantees, and neither one follows from the other. Both guarantees are necessary if X::move is supposed to have the same sort of semantics as memmove (which was clearly the intent), and both guarantees are necessary if X::move is actually supposed to be useful.

Proposed resolution:

ITEM 1: In 21.3.5.4 [lib.string::insert], change paragraph 16 to
EFFECTS: Equivalent to insert(p - begin(), basic_string(first, last)).
ITEM 2: Not a defect; the Standard is clear.. There are ten versions of replace() in the synopsis, and ten versions in 21.3.5.6 [lib.string::replace].
ITEM 3: Change the declaration of push_back in the string synopsis (21.3, [lib.basic.string]) from:

void push_back(const charT)
to
void push_back(charT)
Add the following text immediately after 21.3.5.2 [lib.string::append], paragraph 10.
void basic_string::push_back(charT c);
EFFECTS: Equivalent to append(static_cast<size_type>(1), c);
ITEM 4: Not a defect. The omission appears to have been deliberate.
ITEM 5: Duplicate; see issue 5 (and 87).
ITEM 6: In table 37, Replace:
"Copies correctly even where p is in [s, s+n)."
with:
"Copies correctly even where the ranges [p, p+n) and [s, s+n) overlap."

### 8. Locale::global lacks guarantee

Section: 22.3.1.5 [locale.statics] Status: TC1 Submitter: Matt Austern Opened: 1997-12-24 Last modified: 2008-09-26

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Discussion:

It appears there's an important guarantee missing from clause 22. We're told that invoking locale::global(L) sets the C locale if L has a name. However, we're not told whether or not invoking setlocale(s) sets the global C++ locale.

The intent, I think, is that it should not, but I can't find any such words anywhere.

Proposed resolution:

Add a sentence at the end of 22.3.1.5 [locale.statics], paragraph 2:

> No library function other than `locale::global()` shall affect the value returned by `locale()`.

### 9. Operator new(0) calls should not yield the same pointer

Section: 18.6.1 [new.delete] Status: TC1 Submitter: Steve Clamage Opened: 1998-01-04 Last modified: 2008-09-26

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Discussion:

Scott Meyers, in a comp.std.c++ posting: I just noticed that section 3.7.3.1 of CD2 seems to allow for the possibility that all calls to operator new(0) yield the same pointer, an implementation technique specifically prohibited by ARM 5.3.3.Was this prohibition really lifted? Does the FDIS agree with CD2 in the regard? [Issues list maintainer's note: the IS is the same.]

Proposed resolution:

Change the last paragraph of 3.7.3 from:

> Any allocation and/or deallocation functions defined in a C++ program shall conform to the semantics specified in 3.7.3.1 and 3.7.3.2.

to:

> Any allocation and/or deallocation functions defined in a C++ program, including the default versions in the library, shall conform to the semantics specified in 3.7.3.1 and 3.7.3.2.

Change 3.7.3.1/2, next-to-last sentence, from :

> If the size of the space requested is zero, the value returned shall not be a null pointer value (4.10).

to:

> Even if the size of the space requested is zero, the request can fail. If the request succeeds, the value returned shall be a non-null pointer value (4.10) p0 different from any previously returned value p1, unless that value p1 was since passed to an operator delete.

5.3.4/7 currently reads:

> When the value of the expression in a direct-new-declarator is zero, the allocation function is called to allocate an array with no elements. The pointer returned by the new-expression is non-null. [Note: If the library allocation function is called, the pointer returned is distinct from the pointer to any other object.]

Retain the first sentence, and delete the remainder.

18.5.1 currently has no text. Add the following:

> Except where otherwise specified, the provisions of 3.7.3 apply to the library versions of operator new and operator delete.

To 18.5.1.3, add the following text:

> The provisions of 3.7.3 do not apply to these reserved placement forms of operator new and operator delete.

Rationale:

See 99-0040/N1216, October 22, 1999, by Stephen D. Clamage for the analysis supporting to the proposed resolution.

### 11. Bitset minor problems

Section: 20.3.7 [template.bitset] Status: TC1 Submitter: Matt Austern Opened: 1998-01-22 Last modified: 2008-09-26

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Discussion:

(1) bitset<>::operator[] is mentioned in the class synopsis (23.3.5), but it is not documented in 23.3.5.2.

(2) The class synopsis only gives a single signature for bitset<>::operator[], reference operator[](size_t pos). This doesn't make much sense. It ought to be overloaded on const. reference operator[](size_t pos); bool operator[](size_t pos) const.

(3) Bitset's stream input function (23.3.5.3) ought to skip all whitespace before trying to extract 0s and 1s. The standard doesn't explicitly say that, though. This should go in the Effects clause.

Proposed resolution:

ITEMS 1 AND 2:
In the bitset synopsis (20.3.7 [template.bitset]), replace the member function
`reference operator[](size_t pos);
`
with the two member functions
`bool operator[](size_t pos) const;
reference operator[](size_t pos);
`
Add the following text at the end of 20.3.7.2 [bitset.members], immediately after paragraph 45:

> `bool operator[](size_t pos) const;`
> Requires: pos is valid
> Throws: nothing
> Returns: `test(pos)`
> `bitset<N>::reference operator[](size_t pos);`
> Requires: pos is valid
> Throws: nothing
> Returns: An object of type `bitset<N>::reference` such that `(*this)[pos] == this->test(pos)`, and such that `(*this)[pos] = val` is equivalent to `this->set(pos, val);`

Rationale:

The LWG believes Item 3 is not a defect. "Formatted input" implies the desired semantics. See 27.7.1.2 [istream.formatted].

### 13. Eos refuses to die

Section: 27.7.1.2.3 [istream::extractors] Status: TC1 Submitter: William M. Miller Opened: 1998-03-03 Last modified: 2008-09-26

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Discussion:

In 27.6.1.2.3, there is a reference to "eos", which is the only one in the whole draft (at least using Acrobat search), so it's undefined.

Proposed resolution:

In 27.7.1.2.3 [istream::extractors], replace "eos" with "charT()"

### 14. Locale::combine should be const

Section: 22.3.1.3 [locale.members] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

locale::combine is the only member function of locale (other than constructors and destructor) that is not const. There is no reason for it not to be const, and good reasons why it should have been const. Furthermore, leaving it non-const conflicts with 22.1.1 paragraph 6: "An instance of a locale is immutable."

History: this member function originally was a constructor. it happened that the interface it specified had no corresponding language syntax, so it was changed to a member function. As constructors are never const, there was no "const" in the interface which was transformed into member "combine". It should have been added at that time, but the omission was not noticed.

Proposed resolution:

In 22.3.1 [locale] and also in 22.3.1.3 [locale.members], add "const" to the declaration of member combine:

>     template <class Facet> locale combine(const locale& other) const;

### 15. Locale::name requirement inconsistent

Section: 22.3.1.3 [locale.members] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

locale::name() is described as returning a string that can be passed to a locale constructor, but there is no matching constructor.

Proposed resolution:

In 22.3.1.3 [locale.members], paragraph 5, replace "`locale(name())`" with "`locale(name().c_str())`".

### 16. Bad ctype_byname<char> decl

Section: 22.4.1.4 [locale.codecvt] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The new virtual members ctype_byname<char>::do_widen and do_narrow did not get edited in properly. Instead, the member do_widen appears four times, with wrong argument lists.

Proposed resolution:

The correct declarations for the overloaded members `do_narrow` and `do_widen` should be copied from 22.4.1.3 [facet.ctype.special].

### 17. Bad bool parsing

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

This section describes the process of parsing a text boolean value from the input stream. It does not say it recognizes either of the sequences "true" or "false" and returns the corresponding bool value; instead, it says it recognizes only one of those sequences, and chooses which according to the received value of a reference argument intended for returning the result, and reports an error if the other sequence is found. (!) Furthermore, it claims to get the names from the ctype<> facet rather than the numpunct<> facet, and it examines the "boolalpha" flag wrongly; it doesn't define the value "loc"; and finally, it computes wrongly whether to use numeric or "alpha" parsing.
I believe the correct algorithm is "as if":

      // in, err, val, and str are arguments.
      err = 0;
      const numpunct<charT>& np = use_facet<numpunct<charT> >(str.getloc());
      const string_type t = np.truename(), f = np.falsename();
      bool tm = true, fm = true;
      size_t pos = 0;
      while (tm && pos < t.size() || fm && pos < f.size()) {
        if (in == end) { err = str.eofbit; }
        bool matched = false;
        if (tm && pos < t.size()) {
          if (!err && t[pos] == *in) matched = true;
          else tm = false;
        }
        if (fm && pos < f.size()) {
          if (!err && f[pos] == *in) matched = true;
          else fm = false;
        }
        if (matched) { ++in; ++pos; }
        if (pos > t.size()) tm = false;
        if (pos > f.size()) fm = false;
      }
      if (tm == fm || pos == 0) { err |= str.failbit; }
      else                      { val = tm; }
      return in;

Notice this works reasonably when the candidate strings are both empty, or equal, or when one is a substring of the other. The proposed text below captures the logic of the code above.

Proposed resolution:

In 22.4.2.1.2 [facet.num.get.virtuals], in the first line of paragraph 14, change "&&" to "&".

Then, replace paragraphs 15 and 16 as follows:

> Otherwise target sequences are determined "as if" by calling the members `falsename()` and `truename()` of the facet obtained by `use_facet<numpunct<charT> >(str.getloc())`. Successive characters in the range `[in,end)` (see [lib.sequence.reqmts]) are obtained and matched against corresponding positions in the target sequences only as necessary to identify a unique match. The input iterator `in` is compared to `end` only when necessary to obtain a character. If and only if a target sequence is uniquely matched, `val` is set to the corresponding value.

> The `in` iterator is always left pointing one position beyond the last character successfully matched. If `val` is set, then err is set to `str.goodbit`; or to `str.eofbit` if, when seeking another character to match, it is found that `(in==end)`. If `val` is not set, then err is set to `str.failbit`; or to `(str.failbit|str.eofbit)`if the reason for the failure was that `(in==end)`. [Example: for targets `true`:"a" and `false`:"abb", the input sequence "a" yields `val==true` and `err==str.eofbit`; the input sequence "abc" yields `err=str.failbit`, with `in` ending at the 'c' element. For targets `true`:"1" and `false`:"0", the input sequence "1" yields `val==true` and `err=str.goodbit`. For empty targets (""), any input sequence yields `err==str.failbit`. --end example]

### 18. Get(...bool&) omitted

Section: 22.4.2.1.1 [facet.num.get.members] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

In the list of num_get<> non-virtual members on page 22-23, the member that parses bool values was omitted from the list of definitions of non-virtual members, though it is listed in the class definition and the corresponding virtual is listed everywhere appropriate.

Proposed resolution:

Add at the beginning of 22.4.2.1.1 [facet.num.get.members] another get member for bool&, copied from the entry in 22.4.2.1 [locale.num.get].

### 19. "Noconv" definition too vague

Section: 22.4.1.4 [locale.codecvt] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Duplicate of: 10

Discussion:

In the definitions of codecvt<>::do_out and do_in, they are specified to return noconv if "no conversion is needed". This definition is too vague, and does not say normatively what is done with the buffers.

Proposed resolution:

Change the entry for noconv in the table under paragraph 4 in section 22.4.1.4.2 [locale.codecvt.virtuals] to read:

> `noconv`: `internT` and `externT` are the same type, and input sequence is identical to converted sequence.

Change the Note in paragraph 2 to normative text as follows:

> If returns `noconv`, `internT` and `externT` are the same type and the converted sequence is identical to the input sequence `[from,from_next)`. `to_next` is set equal to `to`, the value of `state` is unchanged, and there are no changes to the values in `[to, to_limit)`.

### 20. Thousands_sep returns wrong type

Section: 22.4.3.1.2 [facet.numpunct.virtuals] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The synopsis for numpunct<>::do_thousands_sep, and the definition of numpunct<>::thousands_sep which calls it, specify that it returns a value of type char_type. Here it is erroneously described as returning a "string_type".

Proposed resolution:

In 22.4.3.1.2 [facet.numpunct.virtuals], above paragraph 2, change "string_type" to "char_type".

### 21. Codecvt_byname<> instantiations

Section: 22.3.1.1.1 [locale.category] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

In the second table in the section, captioned "Required instantiations", the instantiations for codecvt_byname<> have been omitted. These are necessary to allow users to construct a locale by name from facets.

Proposed resolution:

Add in 22.3.1.1.1 [locale.category] to the table captioned "Required instantiations", in the category "ctype" the lines

>     codecvt_byname<char,char,mbstate_t>,
>     codecvt_byname<wchar_t,char,mbstate_t>

### 22. Member open vs. flags

Section: 27.9.1.9 [ifstream.members] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The description of basic_istream<>::open leaves unanswered questions about how it responds to or changes flags in the error status for the stream. A strict reading indicates that it ignores the bits and does not change them, which confuses users who do not expect eofbit and failbit to remain set after a successful open. There are three reasonable resolutions: 1) status quo 2) fail if fail(), ignore eofbit 3) clear failbit and eofbit on call to open().

Proposed resolution:

In 27.9.1.9 [ifstream.members] paragraph 3, and in 27.9.1.13 [ofstream.members] paragraph 3, under open() effects, add a footnote:

> A successful open does not change the error state.

Rationale:

This may seem surprising to some users, but it's just an instance of a general rule: error flags are never cleared by the implementation. The only way error flags are are ever cleared is if the user explicitly clears them by hand.

The LWG believed that preserving this general rule was important enough so that an exception shouldn't be made just for this one case. The resolution of this issue clarifies what the LWG believes to have been the original intent.

### 23. Num_get overflow result

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The current description of numeric input does not account for the possibility of overflow. This is an implicit result of changing the description to rely on the definition of scanf() (which fails to report overflow), and conflicts with the documented behavior of traditional and current implementations.

Users expect, when reading a character sequence that results in a value unrepresentable in the specified type, to have an error reported. The standard as written does not permit this.

Further comments from Dietmar:

I don't feel comfortable with the proposed resolution to issue 23: It kind of simplifies the issue to much. Here is what is going on:

Currently, the behavior of numeric overflow is rather counter intuitive and hard to trace, so I will describe it briefly:

- According to 22.4.2.1.2 [facet.num.get.virtuals] paragraph 11 `failbit` is set if `scanf()` would return an input error; otherwise a value is converted to the rules of `scanf`.
- `scanf()` is defined in terms of `fscanf()`.
- `fscanf()` returns an input failure if during conversion no character matching the conversion specification could be extracted before reaching EOF. This is the only reason for `fscanf()` to fail due to an input error and clearly does not apply to the case of overflow.
- Thus, the conversion is performed according to the rules of `fscanf()` which basically says that `strtod`, `strtol()`, etc. are to be used for the conversion.
- The `strtod()`, `strtol()`, etc. functions consume as many matching characters as there are and on overflow continue to consume matching characters but also return a value identical to the maximum (or minimum for signed types if there was a leading minus) value of the corresponding type and set `errno` to `ERANGE`.
- Thus, according to the current wording in the standard, overflows can be detected! All what is to be done is to check `errno` after reading an element and, of course, clearing `errno` before trying a conversion. With the current wording, it can be detected whether the overflow was due to a positive or negative number for signed types.

Further discussion from Redmond:

The basic problem is that we've defined our behavior, including our error-reporting behavior, in terms of C90. However, C90's method of reporting overflow in scanf is not technically an "input error". The `strto_*` functions are more precise.

There was general consensus that `failbit` should be set upon overflow. We considered three options based on this:

1. Set failbit upon conversion error (including overflow), and don't store any value.
2. Set failbit upon conversion error, and also set `errno` to indicated the precise nature of the error.
3. Set failbit upon conversion error. If the error was due to overflow, store +-numeric_limits<T>::max() as an overflow indication.

Straw poll: (1) 5; (2) 0; (3) 8.

Discussed at Lillehammer. General outline of what we want the solution to look like: we want to say that overflow is an error, and provide a way to distinguish overflow from other kinds of errors. Choose candidate field the same way scanf does, but don't describe the rest of the process in terms of format. If a finite input field is too large (positive or negative) to be represented as a finite value, then set failbit and assign the nearest representable value. Bill will provide wording.

Discussed at Toronto: N2327 is in alignment with the direction we wanted to go with in Lillehammer. Bill to work on.

Proposed resolution:

Change 22.4.2.1.2 [facet.num.get.virtuals], end of p3:

> Stage 3: The result of stage 2 processing can be one of The sequence of `char`s accumulated in stage 2 (the field) is converted to a numeric value by the rules of one of the functions declared in the header `<cstdlib>`:

> - A sequence of `char`s has been accumulated in stage 2 that is converted (according to the rules of `scanf`) to a value of the type of val. This value is stored in val and `ios_base::goodbit` is stored in err. For a signed integer value, the function `strtoll`.
> - The sequence of `char`s accumulated in stage 2 would have caused `scanf` to report an input failure. `ios_base::failbit` is assigned to err. For an unsigned integer value, the function `strtoull`.
> - For a floating-point value, the function `strtold`.

> The numeric value to be stored can be one of:

> - zero, if the conversion function fails to convert the entire field. `ios_base::failbit` is assigned to err.
> - the most positive representable value, if the field represents a value too large positive to be represented in val. `ios_base::failbit` is assigned to err.
> - the most negative representable value (zero for unsigned integer), if the field represents a value too large negative to be represented in val. `ios_base::failbit` is assigned to err.
> - the converted value, otherwise.

> The resultant numeric value is stored in val.

Change 22.4.2.1.2 [facet.num.get.virtuals], p6-p7:

>     iter_type do_get(iter_type in, iter_type end, ios_base& str,
>                      ios_base::iostate& err, bool& val) const;

> > -6- Effects: If `(str.flags()&ios_base::boolalpha)==0` then input proceeds as it would for a `long` except that if a value is being stored into val, the value is determined according to the following: If the value to be stored is 0 then `false` is stored. If the value is 1 then `true` is stored. Otherwise `err|=ios_base::failbit` is performed and no value `true` is stored. and `ios_base::failbit` is assigned to err.

> > -7- Otherwise target sequences are determined "as if" by calling the members `falsename()` and `truename()` of the facet obtained by `use_facet<numpunct<charT> >(str.getloc())`. Successive characters in the range `[in,end)` (see 23.1.1) are obtained and matched against corresponding positions in the target sequences only as necessary to identify a unique match. The input iterator in is compared to end only when necessary to obtain a character. If and only if a target sequence is uniquely matched, val is set to the corresponding value. Otherwise `false` is stored and `ios_base::failbit` is assigned to err.

### 24. "do_convert" doesn't exist

Section: 22.4.1.4 [locale.codecvt] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Duplicate of: 72

Discussion:

The description of codecvt<>::do_out and do_in mentions a symbol "do_convert" which is not defined in the standard. This is a leftover from an edit, and should be "do_in and do_out".

Proposed resolution:

In 22.4.1.4 [locale.codecvt], paragraph 3, change "do_convert" to "do_in or do_out". Also, in 22.4.1.4.2 [locale.codecvt.virtuals], change "do_convert()" to "do_in or do_out".

### 25. String operator<< uses width() value wrong

Section: 21.4.8.9 [string.io] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Duplicate of: 67

Discussion:

In the description of operator<< applied to strings, the standard says that uses the smaller of os.width() and str.size(), to pad "as described in stage 3" elsewhere; but this is inconsistent, as this allows no possibility of space for padding.

Proposed resolution:

Change 21.4.8.9 [string.io] paragraph 4 from:
"... where `n` is the smaller of `os.width()` and `str.size()`; ..."
to:
"... where `n` is the larger of `os.width()` and `str.size()`; ..."

### 26. Bad sentry example

Section: 27.7.1.1.3 [istream::sentry] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

In paragraph 6, the code in the example:

      template <class charT, class traits = char_traits<charT> >
      basic_istream<charT,traits>::sentry(
               basic_istream<charT,traits>& is, bool noskipws = false) {
          ...
          int_type c;
          typedef ctype<charT> ctype_type;
          const ctype_type& ctype = use_facet<ctype_type>(is.getloc());
          while ((c = is.rdbuf()->snextc()) != traits::eof()) {
            if (ctype.is(ctype.space,c)==0) {
              is.rdbuf()->sputbackc (c);
              break;
            }
          }
          ...
       }

fails to demonstrate correct use of the facilities described. In particular, it fails to use traits operators, and specifies incorrect semantics. (E.g. it specifies skipping over the first character in the sequence without examining it.)

Proposed resolution:

Remove the example above from 27.7.1.1.3 [istream::sentry] paragraph 6.

Rationale:

The originally proposed replacement code for the example was not correct. The LWG tried in Kona and again in Tokyo to correct it without success. In Tokyo, an implementor reported that actual working code ran over one page in length and was quite complicated. The LWG decided that it would be counter-productive to include such a lengthy example, which might well still contain errors.

### 27. String::erase(range) yields wrong iterator

Section: 21.4.6.5 [string::erase] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The string::erase(iterator first, iterator last) is specified to return an element one place beyond the next element after the last one erased. E.g. for the string "abcde", erasing the range ['b'..'d') would yield an iterator for element 'e', while 'd' has not been erased.

Proposed resolution:

In 21.4.6.5 [string::erase], paragraph 10, change:

> Returns: an iterator which points to the element immediately following _last_ prior to the element being erased.

to read

> Returns: an iterator which points to the element pointed to by _last_ prior to the other elements being erased.

### 28. Ctype<char>is ambiguous

Section: 22.4.1.3.2 [facet.ctype.char.members] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Duplicate of: 236

Discussion:

The description of the vector form of ctype<char>::is can be interpreted to mean something very different from what was intended. Paragraph 4 says

> Effects: The second form, for all *p in the range [low, high), assigns vec[p-low] to table()[(unsigned char)*p].

This is intended to copy the value indexed from table()[] into the place identified in vec[].

Proposed resolution:

Change 22.4.1.3.2 [facet.ctype.char.members], paragraph 4, to read

> Effects: The second form, for all *p in the range [low, high), assigns into vec[p-low] the value table()[(unsigned char)*p].

### 29. Ios_base::init doesn't exist

Section: 27.4.1 [narrow.stream.objects] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

Sections 27.4.1 [narrow.stream.objects] and 27.4.2 [wide.stream.objects] mention a function ios_base::init, which is not defined. Probably they mean basic_ios<>::init, defined in 27.5.4.1 [basic.ios.cons], paragraph 3.

Proposed resolution:

[R12: modified to include paragraph 5.]

In 27.4.1 [narrow.stream.objects] paragraph 2 and 5, change

> ios_base::init

to

> basic_ios<char>::init

Also, make a similar change in 27.4.2 [wide.stream.objects] except it should read

> basic_ios<wchar_t>::init

### 30. Wrong header for LC_*

Section: 22.3.1.1.1 [locale.category] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

Paragraph 2 implies that the C macros LC_CTYPE etc. are defined in <cctype>, where they are in fact defined elsewhere to appear in <clocale>.

Proposed resolution:

In 22.3.1.1.1 [locale.category], paragraph 2, change "<cctype>" to read "<clocale>".

### 31. Immutable locale values

Section: 22.3.1 [locale] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Duplicate of: 378

Discussion:

Paragraph 6, says "An instance of `locale` is immutable; once a facet reference is obtained from it, ...". This has caused some confusion, because locale variables are manifestly assignable.

Proposed resolution:

In 22.3.1 [locale] replace paragraph 6

> An instance of `locale` is immutable; once a facet reference is obtained from it, that reference remains usable as long as the locale value itself exists.

with

> Once a facet reference is obtained from a locale object by calling use_facet<>, that reference remains usable, and the results from member functions of it may be cached and re-used, as long as some locale object refers to that facet.

### 32. Pbackfail description inconsistent

Section: 27.6.2.4.4 [streambuf.virt.pback] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The description of the required state before calling virtual member basic_streambuf<>::pbackfail requirements is inconsistent with the conditions described in 27.5.2.2.4 [lib.streambuf.pub.pback] where member sputbackc calls it. Specifically, the latter says it calls pbackfail if:

traits::eq(c,gptr()[-1]) is false

where pbackfail claims to require:

traits::eq(*gptr(),traits::to_char_type(c)) returns false

It appears that the pbackfail description is wrong.

Proposed resolution:

In 27.6.2.4.4 [streambuf.virt.pback], paragraph 1, change:

> "`traits::eq(*gptr(),traits::to_char_type( c))`"

to

> "`traits::eq(traits::to_char_type(c),gptr()[-1])`"

Rationale:

Note deliberate reordering of arguments for clarity in addition to the correction of the argument value.

### 33. Codecvt<> mentions from_type

Section: 22.4.1.4 [locale.codecvt] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Duplicate of: 43

Discussion:

In the table defining the results from do_out and do_in, the specification for the result error says

> encountered a from_type character it could not convert

but from_type is not defined. This clearly is intended to be an externT for do_in, or an internT for do_out.

Proposed resolution:

In 22.4.1.4.2 [locale.codecvt.virtuals] paragraph 4, replace the definition in the table for the case of _error_ with

> encountered a character in `[from,from_end)` that it could not convert.

### 34. True/falsename() not in ctype<>

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

In paragraph 19, Effects:, members truename() and falsename are used from facet ctype<charT>, but it has no such members. Note that this is also a problem in 22.2.2.1.2, addressed in (4).

Proposed resolution:

In 22.4.2.2.2 [facet.num.put.virtuals], paragraph 19, in the Effects: clause for member put(...., bool), replace the initialization of the string_type value s as follows:

>     const numpunct& np = use_facet<numpunct<charT> >(loc);
>     string_type s = val ? np.truename() : np.falsename();

### 35. No manipulator unitbuf in synopsis

Section: 27.5 [iostreams.base] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

In 27.5.5.1 [fmtflags.manip], we have a definition for a manipulator named "unitbuf". Unlike other manipulators, it's not listed in synopsis. Similarly for "nounitbuf".

Proposed resolution:

Add to the synopsis for <ios> in 27.5 [iostreams.base], after the entry for "nouppercase", the prototypes:

>     ios_base& unitbuf(ios_base& str);
>     ios_base& nounitbuf(ios_base& str);

### 36. Iword & pword storage lifetime omitted

Section: 27.5.2.5 [ios.base.storage] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

In the definitions for ios_base::iword and pword, the lifetime of the storage is specified badly, so that an implementation which only keeps the last value stored appears to conform. In particular, it says:

The reference returned may become invalid after another call to the object's iword member with a different index ...

This is not idle speculation; at least one implementation was done this way.

Proposed resolution:

Add in 27.5.2.5 [ios.base.storage], in both paragraph 2 and also in paragraph 4, replace the sentence:

> The reference returned may become invalid after another call to the object's iword [pword] member with a different index, after a call to its copyfmt member, or when the object is destroyed.

with:

> The reference returned is invalid after any other operations on the object. However, the value of the storage referred to is retained, so that until the next call to copyfmt, calling iword [pword] with the same index yields another reference to the same value.

substituting "iword" or "pword" as appropriate.

### 37. Leftover "global" reference

Section: 22.3.1 [locale] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

In the overview of locale semantics, paragraph 4, is the sentence

> If Facet is not present in a locale (or, failing that, in the global locale), it throws the standard exception bad_cast.

This is not supported by the definition of use_facet<>, and represents semantics from an old draft.

Proposed resolution:

In 22.3.1 [locale], paragraph 4, delete the parenthesized expression

> (or, failing that, in the global locale)

### 38. Facet definition incomplete

Section: 22.3.2 [locale.global.templates] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

It has been noticed by Esa Pulkkinen that the definition of "facet" is incomplete. In particular, a class derived from another facet, but which does not define a member id, cannot safely serve as the argument F to use_facet<F>(loc), because there is no guarantee that a reference to the facet instance stored in loc is safely convertible to F.

Proposed resolution:

In the definition of std::use_facet<>(), replace the text in paragraph 1 which reads:

> Get a reference to a facet of a locale.

with:

> Requires: `Facet` is a facet class whose definition contains the public static member `id` as defined in 22.3.1.1.2 [locale.facet].

[ Kona: strike as overspecification the text "(not inherits)" from the original resolution, which read "... whose definition contains (not inherits) the public static member `id`..." ]

### 39. istreambuf_iterator<>::operator++(int) definition garbled

Section: 24.6.3.4 [istreambuf.iterator::op++] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

Following the definition of istreambuf_iterator<>::operator++(int) in paragraph 3, the standard contains three lines of garbage text left over from a previous edit.

>     istreambuf_iterator<charT,traits> tmp = *this;
>     sbuf_->sbumpc();
>     return(tmp);

Proposed resolution:

In 24.6.3.4 [istreambuf.iterator::op++], delete the three lines of code at the end of paragraph 3.

### 40. Meaningless normative paragraph in examples

Section: 22.4.8 [facets.examples] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

Paragraph 3 of the locale examples is a description of part of an implementation technique that has lost its referent, and doesn't mean anything.

Proposed resolution:

Delete 22.4.8 [facets.examples] paragraph 3 which begins "This initialization/identification system depends...", or (at the editor's option) replace it with a place-holder to keep the paragraph numbering the same.

### 41. Ios_base needs clear(), exceptions()

Section: 27.5.2 [ios.base] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Duplicate of: 157

Discussion:

The description of ios_base::iword() and pword() in 27.5.2.4 [ios.members.static], say that if they fail, they "set badbit, which may throw an exception". However, ios_base offers no interface to set or to test badbit; those interfaces are defined in basic_ios<>.

Proposed resolution:

Change the description in 27.5.2.5 [ios.base.storage] in paragraph 2, and also in paragraph 4, as follows. Replace

> If the function fails it sets badbit, which may throw an exception.

with

> If the function fails, and `*this` is a base sub-object of a `basic_ios<>` object or sub-object, the effect is equivalent to calling `basic_ios<>::setstate(badbit)` on the derived object (which may throw `failure`).

[Kona: LWG reviewed wording; setstate(failbit) changed to setstate(badbit).]

### 42. String ctors specify wrong default allocator

Section: 21.4 [basic.string] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The basic_string<> copy constructor:

    basic_string(const basic_string& str, size_type pos = 0,
                 size_type n = npos, const Allocator& a = Allocator());

specifies an Allocator argument default value that is counter-intuitive. The natural choice for a the allocator to copy from is str.get_allocator(). Though this cannot be expressed in default-argument notation, overloading suffices.

Alternatively, the other containers in Clause 23 (deque, list, vector) do not have this form of constructor, so it is inconsistent, and an evident source of confusion, for basic_string<> to have it, so it might better be removed.

Proposed resolution:

In 21.4 [basic.string], replace the declaration of the copy constructor as follows:

>     basic_string(const basic_string& str);
>     basic_string(const basic_string& str, size_type pos, size_type n = npos,
>                  const Allocator& a = Allocator());

In 21.4.1 [string.require], replace the copy constructor declaration as above. Add to paragraph 5, Effects:

> In the first form, the Allocator value used is copied from `str.get_allocator()`.

Rationale:

The LWG believes the constructor is actually broken, rather than just an unfortunate design choice.

The LWG considered two other possible resolutions:

A. In 21.4 [basic.string], replace the declaration of the copy constructor as follows:

>     basic_string(const basic_string& str, size_type pos = 0,
>                  size_type n = npos);
>     basic_string(const basic_string& str, size_type pos,
>                  size_type n, const Allocator& a);

In 21.4.1 [string.require], replace the copy constructor declaration as above. Add to paragraph 5, Effects:

> When no `Allocator` argument is provided, the string is constructed using the value `str.get_allocator()`.

B. In 21.4 [basic.string], and also in 21.4.1 [string.require], replace the declaration of the copy constructor as follows:

>     basic_string(const basic_string& str, size_type pos = 0,
>                  size_type n = npos);

The proposed resolution reflects the original intent of the LWG. It was also noted by Pete Becker that this fix "will cause a small amount of existing code to now work correctly."

[ Kona: issue editing snafu fixed - the proposed resolution now correctly reflects the LWG consensus. ]

### 44. Iostreams use operator== on int_type values

Section: 27 [input.output] Status: CD1 Submitter: Nathan Myers Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

Many of the specifications for iostreams specify that character values or their int_type equivalents are compared using operators == or !=, though in other places traits::eq() or traits::eq_int_type is specified to be used throughout. This is an inconsistency; we should change uses of == and != to use the traits members instead.

Proposed resolution:

[Pre-Kona: Dietmar supplied wording]

List of changes to clause 27:

1. In lib.basic.ios.members paragraph 13 (postcondition clause for 'fill(cT)') change

   >          fillch == fill()

   to

   >          traits::eq(fillch, fill())

2. In lib.istream.unformatted paragraph 7 (effects clause for 'get(cT,streamsize,cT)'), third bullet, change

   >          c == delim for the next available input character c

   to

   >          traits::eq(c, delim) for the next available input character c

3. In lib.istream.unformatted paragraph 12 (effects clause for 'get(basic_streambuf<cT,Tr>&,cT)'), third bullet, change

   >          c == delim for the next available input character c

   to

   >          traits::eq(c, delim) for the next available input character c

4. In lib.istream.unformatted paragraph 17 (effects clause for 'getline(cT,streamsize,cT)'), second bullet, change

   >          c == delim for the next available input character c

   to

   >          traits::eq(c, delim) for the next available input character c

5. In lib.istream.unformatted paragraph 24 (effects clause for 'ignore(int,int_type)'), second bullet, change

   >          c == delim for the next available input character c

   to

   >          traits::eq_int_type(c, delim) for the next available input
   >          character c

6. In lib.istream.unformatted paragraph 25 (notes clause for 'ignore(int,int_type)'), second bullet, change

   >          The last condition will never occur if delim == traits::eof()

   to

   >          The last condition will never occur if
   >          traits::eq_int_type(delim, traits::eof()).

7. In lib.istream.sentry paragraph 6 (example implementation for the sentry constructor) change

   >          while ((c = is.rdbuf()->snextc()) != traits::eof()) {

   to

   >          while (!traits::eq_int_type(c = is.rdbuf()->snextc(), traits::eof())) {

List of changes to Chapter 21:

1. In lib.string::find paragraph 1 (effects clause for find()), second bullet, change

   >          at(xpos+I) == str.at(I) for all elements ...

   to

   >          traits::eq(at(xpos+I), str.at(I)) for all elements ...

2. In lib.string::rfind paragraph 1 (effects clause for rfind()), second bullet, change

   >          at(xpos+I) == str.at(I) for all elements ...

   to

   >          traits::eq(at(xpos+I), str.at(I)) for all elements ...

3. In lib.string::find.first.of paragraph 1 (effects clause for find_first_of()), second bullet, change

   >          at(xpos+I) == str.at(I) for all elements ...

   to

   >          traits::eq(at(xpos+I), str.at(I)) for all elements ...

4. In lib.string::find.last.of paragraph 1 (effects clause for find_last_of()), second bullet, change

   >          at(xpos+I) == str.at(I) for all elements ...

   to

   >          traits::eq(at(xpos+I), str.at(I)) for all elements ...

5. In lib.string::find.first.not.of paragraph 1 (effects clause for find_first_not_of()), second bullet, change

   >          at(xpos+I) == str.at(I) for all elements ...

   to

   >          traits::eq(at(xpos+I), str.at(I)) for all elements ...

6. In lib.string::find.last.not.of paragraph 1 (effects clause for find_last_not_of()), second bullet, change

   >          at(xpos+I) == str.at(I) for all elements ...

   to

   >          traits::eq(at(xpos+I), str.at(I)) for all elements ...

7. In lib.string.ios paragraph 5 (effects clause for getline()), second bullet, change

   >          c == delim for the next available input character c

   to

   >          traits::eq(c, delim) for the next available input character c

Notes:

- Fixing this issue highlights another sloppyness in lib.istream.unformatted paragraph 24: this clause mentions a "character" which is then compared to an 'int_type' (see item 5. in the list below). It is not clear whether this requires explicit words and if so what these words are supposed to be. A similar issue exists, BTW, for operator*() of istreambuf_iterator which returns the result of sgetc() as a character type (see lib.istreambuf.iterator::op* paragraph 1), and for operator++() of istreambuf_iterator which passes the result of sbumpc() to a constructor taking a char_type (see lib.istreambuf.iterator::operator++ paragraph 3). Similarily, the assignment operator ostreambuf_iterator passes a char_type to a function taking an int_type (see lib.ostreambuf.iter.ops paragraph 1).
- It is inconsistent to use comparisons using the traits functions in Chapter 27 while not using them in Chapter 21, especially as some of the inconsistent uses actually involve streams (eg. getline() on streams). To avoid leaving this issue open still longer due to this inconsistency (it is open since 1998), a list of changes to Chapter 21 is below.
- In Chapter 24 there are several places with statements like "the end of stream is reached (streambuf_type::sgetc() returns traits::eof())" (lib.istreambuf.iterator paragraph 1, lib.ostreambuf.iter.ops paragraph 5). It is unclear whether these should be clarified to use traits::eq_int_type() for detecting traits::eof().

### 46. Minor Annex D errors

Section: D.8 [depr.str.strstreams] Status: TC1 Submitter: Brendan Kehoe Opened: 1998-06-01 Last modified: 2008-09-26

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Discussion:

See lib-6522 and edit-814.

Proposed resolution:

Change D.8.1 [depr.strstreambuf] (since streambuf is a typedef of basic_streambuf<char>) from:

             virtual streambuf<char>* setbuf(char* s, streamsize n);

to:

             virtual streambuf* setbuf(char* s, streamsize n);

In D.8.4 [depr.strstream] insert the semicolon now missing after int_type:

         namespace std {
           class strstream
             : public basic_iostream<char> {
           public:
             // Types
             typedef char                                char_type;
             typedef typename char_traits<char>::int_type int_type
             typedef typename char_traits<char>::pos_type pos_type;

### 47. Imbue() and getloc() Returns clauses swapped

Section: 27.5.2.3 [ios.base.locales] Status: TC1 Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2008-09-26

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Discussion:

Section 27.4.2.3 specifies how imbue() and getloc() work. That section has two RETURNS clauses, and they make no sense as stated. They make perfect sense, though, if you swap them. Am I correct in thinking that paragraphs 2 and 4 just got mixed up by accident?

Proposed resolution:

In 27.5.2.3 [ios.base.locales] swap paragraphs 2 and 4.

### 48. Use of non-existent exception constructor

Section: 27.5.2.1.1 [ios::failure] Status: TC1 Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2008-09-26

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Discussion:

27.4.2.1.1, paragraph 2, says that class failure initializes the base class, exception, with exception(msg). Class exception (see 18.6.1) has no such constructor.

Proposed resolution:

Replace 27.5.2.1.1 [ios::failure], paragraph 2, with

> EFFECTS: Constructs an object of class `failure`.

### 49. Underspecification of ios_base::sync_with_stdio

Section: 27.5.2.4 [ios.members.static] Status: CD1 Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2008-09-26

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Discussion:

Two problems

(1) 27.4.2.4 doesn't say what ios_base::sync_with_stdio(f) returns. Does it return f, or does it return the previous synchronization state? My guess is the latter, but the standard doesn't say so.

(2) 27.4.2.4 doesn't say what it means for streams to be synchronized with stdio. Again, of course, I can make some guesses. (And I'm unhappy about the performance implications of those guesses, but that's another matter.)

Proposed resolution:

Change the following sentence in 27.5.2.4 [ios.members.static] returns clause from:

> `true` if the standard iostream objects (27.3) are synchronized and otherwise returns `false`.

to:

> `true` if the previous state of the standard iostream objects (27.3) was synchronized and otherwise returns `false`.

Add the following immediately after 27.5.2.4 [ios.members.static], paragraph 2:

> When a standard iostream object str is synchronized with a standard stdio stream f, the effect of inserting a character c by

>       fputc(f, c);

> is the same as the effect of

>       str.rdbuf()->sputc(c);

> for any sequence of characters; the effect of extracting a character c by

>       c = fgetc(f);

> is the same as the effect of:

>       c = str.rdbuf()->sbumpc(c);

> for any sequences of characters; and the effect of pushing back a character c by

>       ungetc(c, f);

> is the same as the effect of

>       str.rdbuf()->sputbackc(c);

> for any sequence of characters. [Footnote: This implies that operations on a standard iostream object can be mixed arbitrarily with operations on the corresponding stdio stream. In practical terms, synchronization usually means that a standard iostream object and a standard stdio object share a buffer. --End Footnote]

[pre-Copenhagen: PJP and Matt contributed the definition of "synchronization"]

[post-Copenhagen: proposed resolution was revised slightly: text was added in the non-normative footnote to say that operations on the two streams can be mixed arbitrarily.]

### 50. Copy constructor and assignment operator of ios_base

Section: 27.5.2 [ios.base] Status: TC1 Submitter: Matt Austern Opened: 1998-06-21 Last modified: 2008-09-26

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Discussion:

As written, ios_base has a copy constructor and an assignment operator. (Nothing in the standard says it doesn't have one, and all classes have copy constructors and assignment operators unless you take specific steps to avoid them.) However, nothing in 27.4.2 says what the copy constructor and assignment operator do.

My guess is that this was an oversight, that ios_base is, like basic_ios, not supposed to have a copy constructor or an assignment operator.

Jerry Schwarz comments: Yes, its an oversight, but in the opposite sense to what you're suggesting. At one point there was a definite intention that you could copy ios_base. It's an easy way to save the entire state of a stream for future use. As you note, to carry out that intention would have required a explicit description of the semantics (e.g. what happens to the iarray and parray stuff).

Proposed resolution:

In 27.5.2 [ios.base], class ios_base, specify the copy constructor and operator= members as being private.

Rationale:

The LWG believes the difficulty of specifying correct semantics outweighs any benefit of allowing ios_base objects to be copyable.

### 51. Requirement to not invalidate iterators missing

Section: 23.2 [container.requirements] Status: TC1 Submitter: David Vandevoorde Opened: 1998-06-23 Last modified: 2008-09-26

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Discussion:

The std::sort algorithm can in general only sort a given sequence by moving around values. The list<>::sort() member on the other hand could move around values or just update internal pointers. Either method can leave iterators into the list<> dereferencable, but they would point to different things.

Does the FDIS mandate anywhere which method should be used for list<>::sort()?

Matt Austern comments:

I think you've found an omission in the standard.

The library working group discussed this point, and there was supposed to be a general requirement saying that list, set, map, multiset, and multimap may not invalidate iterators, or change the values that iterators point to, except when an operation does it explicitly. So, for example, insert() doesn't invalidate any iterators and erase() and remove() only invalidate iterators pointing to the elements that are being erased.

I looked for that general requirement in the FDIS, and, while I found a limited form of it for the sorted associative containers, I didn't find it for list. It looks like it just got omitted.

The intention, though, is that list<>::sort does not invalidate any iterators and does not change the values that any iterator points to. There would be no reason to have the member function otherwise.

Proposed resolution:

Add a new paragraph at the end of 23.1:

> Unless otherwise specified (either explicitly or by defining a function in terms of other functions), invoking a container member function or passing a container as an argument to a library function shall not invalidate iterators to, or change the values of, objects within that container.

Rationale:

This was US issue CD2-23-011; it was accepted in London but the change was not made due to an editing oversight. The wording in the proposed resolution below is somewhat updated from CD2-23-011, particularly the addition of the phrase "or change the values of"

### 52. Small I/O problems

Section: 27.5.3.2 [fpos.operations] Status: TC1 Submitter: Matt Austern Opened: 1998-06-23 Last modified: 2008-09-26

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Discussion:

First, 27.5.4.1 [basic.ios.cons], table 89. This is pretty obvious: it should be titled "basic_ios<>() effects", not "ios_base() effects".

[The second item is a duplicate; see issue 6 for resolution.]

Second, 27.5.3.2 [fpos.operations] table 88 . There are a couple different things wrong with it, some of which I've already discussed with Jerry, but the most obvious mechanical sort of error is that it uses expressions like P(i) and p(i), without ever defining what sort of thing "i" is.

(The other problem is that it requires support for streampos arithmetic. This is impossible on some systems, i.e. ones where file position is a complicated structure rather than just a number. Jerry tells me that the intention was to require syntactic support for streampos arithmetic, but that it wasn't actually supposed to do anything meaningful except on platforms, like Unix, where genuine arithmetic is possible.)

Proposed resolution:

Change 27.5.4.1 [basic.ios.cons] table 89 title from "ios_base() effects" to "basic_ios<>() effects".

### 53. Basic_ios destructor unspecified

Section: 27.5.4.1 [basic.ios.cons] Status: TC1 Submitter: Matt Austern Opened: 1998-06-23 Last modified: 2008-09-26

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Discussion:

There's nothing in 27.4.4 saying what basic_ios's destructor does. The important question is whether basic_ios::~basic_ios() destroys rdbuf().

Proposed resolution:

Add after 27.5.4.1 [basic.ios.cons] paragraph 2:

> `virtual ~basic_ios();`

> Notes: The destructor does not destroy `rdbuf()`.

Rationale:

The LWG reviewed the additional question of whether or not `rdbuf(0)` may set `badbit`. The answer is clearly yes; it may be set via `clear()`. See 27.5.4.2 [basic.ios.members], paragraph 6. This issue was reviewed at length by the LWG, which removed from the original proposed resolution a footnote which incorrectly said "`rdbuf(0)` does not set `badbit`".

### 54. Basic_streambuf's destructor

Section: 27.6.2.1 [streambuf.cons] Status: TC1 Submitter: Matt Austern Opened: 1998-06-25 Last modified: 2008-09-26

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Discussion:

The class synopsis for basic_streambuf shows a (virtual) destructor, but the standard doesn't say what that destructor does. My assumption is that it does nothing, but the standard should say so explicitly.

Proposed resolution:

Add after 27.6.2.1 [streambuf.cons] paragraph 2:

> `virtual ~basic_streambuf();`

> Effects: None.

### 55. Invalid stream position is undefined

Section: 27 [input.output] Status: TC1 Submitter: Matt Austern Opened: 1998-06-26 Last modified: 2008-09-26

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Discussion:

Several member functions in clause 27 are defined in certain circumstances to return an "invalid stream position", a term that is defined nowhere in the standard. Two places (27.5.2.4.2, paragraph 4, and 27.8.1.4, paragraph 15) contain a cross-reference to a definition in _lib.iostreams.definitions_, a nonexistent section.

I suspect that the invalid stream position is just supposed to be pos_type(-1). Probably best to say explicitly in (for example) 27.5.2.4.2 that the return value is pos_type(-1), rather than to use the term "invalid stream position", define that term somewhere, and then put in a cross-reference.

The phrase "invalid stream position" appears ten times in the C++ Standard. In seven places it refers to a return value, and it should be changed. In three places it refers to an argument, and it should not be changed. Here are the three places where "invalid stream position" should not be changed:

> 27.8.1.4 [stringbuf.virtuals], paragraph 14
> 27.9.1.5 [filebuf.virtuals], paragraph 14
> D.8.1.3 [depr.strstreambuf.virtuals], paragraph 17

Proposed resolution:

In 27.6.2.4.2 [streambuf.virt.buffer], paragraph 4, change "Returns an object of class pos_type that stores an invalid stream position (_lib.iostreams.definitions_)" to "Returns `pos_type(off_type(-1))`".

In 27.6.2.4.2 [streambuf.virt.buffer], paragraph 6, change "Returns an object of class pos_type that stores an invalid stream position" to "Returns `pos_type(off_type(-1))`".

In 27.8.1.4 [stringbuf.virtuals], paragraph 13, change "the object stores an invalid stream position" to "the return value is `pos_type(off_type(-1))`".

In 27.9.1.5 [filebuf.virtuals], paragraph 13, change "returns an invalid stream position (27.4.3)" to "returns `pos_type(off_type(-1))`"

In 27.9.1.5 [filebuf.virtuals], paragraph 15, change "Otherwise returns an invalid stream position (_lib.iostreams.definitions_)" to "Otherwise returns `pos_type(off_type(-1))`"

In D.8.1.3 [depr.strstreambuf.virtuals], paragraph 15, change "the object stores an invalid stream position" to "the return value is `pos_type(off_type(-1))`"

In D.8.1.3 [depr.strstreambuf.virtuals], paragraph 18, change "the object stores an invalid stream position" to "the return value is `pos_type(off_type(-1))`"

### 56. Showmanyc's return type

Section: 27.6.2 [streambuf] Status: TC1 Submitter: Matt Austern Opened: 1998-06-29 Last modified: 2008-09-26

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Discussion:

The class summary for basic_streambuf<>, in 27.5.2, says that showmanyc has return type int. However, 27.5.2.4.3 says that its return type is streamsize.

Proposed resolution:

Change `showmanyc`'s return type in the 27.6.2 [streambuf] class summary to `streamsize`.

### 57. Mistake in char_traits

Section: 21.2.3.4 [char.traits.specializations.wchar.t] Status: TC1 Submitter: Matt Austern Opened: 1998-07-01 Last modified: 2008-09-26

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Discussion:

21.1.3.2, paragraph 3, says "The types streampos and wstreampos may be different if the implementation supports no shift encoding in narrow-oriented iostreams but supports one or more shift encodings in wide-oriented streams".

That's wrong: the two are the same type. The <iosfwd> summary in 27.2 says that streampos and wstreampos are, respectively, synonyms for fpos<char_traits<char>::state_type> and fpos<char_traits<wchar_t>::state_type>, and, flipping back to clause 21, we see in 21.1.3.1 and 21.1.3.2 that char_traits<char>::state_type and char_traits<wchar_t>::state_type must both be mbstate_t.

Proposed resolution:

Remove the sentence in 21.2.3.4 [char.traits.specializations.wchar.t] paragraph 3 which begins "The types streampos and wstreampos may be different..." .

### 59. Ambiguity in specification of gbump

Section: 27.6.2.3.2 [streambuf.get.area] Status: TC1 Submitter: Matt Austern Opened: 1998-07-28 Last modified: 2008-09-26

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Discussion:

27.5.2.3.1 says that basic_streambuf::gbump() "Advances the next pointer for the input sequence by n."

The straightforward interpretation is that it is just gptr() += n. An alternative interpretation, though, is that it behaves as if it calls sbumpc n times. (The issue, of course, is whether it might ever call underflow.) There is a similar ambiguity in the case of pbump.

(The "classic" AT&T implementation used the former interpretation.)

Proposed resolution:

Change 27.6.2.3.2 [streambuf.get.area] paragraph 4 gbump effects from:

> Effects: Advances the next pointer for the input sequence by n.

to:

> Effects: Adds `n` to the next pointer for the input sequence.

Make the same change to 27.6.2.3.3 [streambuf.put.area] paragraph 4 pbump effects.

### 60. What is a formatted input function?

Section: 27.7.1.2.1 [istream.formatted.reqmts] Status: TC1 Submitter: Matt Austern Opened: 1998-08-03 Last modified: 2008-09-26

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Duplicate of: 162, 163, 166

Discussion:

Paragraph 1 of 27.6.1.2.1 contains general requirements for all formatted input functions. Some of the functions defined in section 27.6.1.2 explicitly say that those requirements apply ("Behaves like a formatted input member (as described in 27.6.1.2.1)"), but others don't. The question: is 27.6.1.2.1 supposed to apply to everything in 27.6.1.2, or only to those member functions that explicitly say "behaves like a formatted input member"? Or to put it differently: are we to assume that everything that appears in a section called "Formatted input functions" really is a formatted input function? I assume that 27.6.1.2.1 is intended to apply to the arithmetic extractors (27.6.1.2.2), but I assume that it is not intended to apply to extractors like

        basic_istream& operator>>(basic_istream& (*pf)(basic_istream&));

and

        basic_istream& operator>>(basic_streammbuf*);

There is a similar ambiguity for unformatted input, formatted output, and unformatted output.

Comments from Judy Ward: It seems like the problem is that the basic_istream and basic_ostream operator <<()'s that are used for the manipulators and streambuf* are in the wrong section and should have their own separate section or be modified to make it clear that the "Common requirements" listed in section 27.6.1.2.1 (for basic_istream) and section 27.6.2.5.1 (for basic_ostream) do not apply to them.

Additional comments from Dietmar Kühl: It appears to be somewhat nonsensical to consider the functions defined in 27.7.1.2.3 [istream::extractors] paragraphs 1 to 5 to be "Formatted input function" but since these functions are defined in a section labeled "Formatted input functions" it is unclear to me whether these operators are considered formatted input functions which have to conform to the "common requirements" from 27.7.1.2.1 [istream.formatted.reqmts]: If this is the case, all manipulators, not just `ws`, would skip whitespace unless `noskipws` is set (... but setting `noskipws` using the manipulator syntax would also skip whitespace :-)

It is not clear which functions are to be considered unformatted input functions. As written, it seems that all functions in 27.7.1.3 [istream.unformatted] are unformatted input functions. However, it does not really make much sense to construct a sentry object for `gcount()`, `sync()`, ... Also it is unclear what happens to the `gcount()` if eg. `gcount()`, `putback()`, `unget()`, or `sync()` is called: These functions don't extract characters, some of them even "unextract" a character. Should this still be reflected in `gcount()`? Of course, it could be read as if after a call to `gcount()` `gcount()` return `0` (the last unformatted input function, `gcount()`, didn't extract any character) and after a call to `putback()` `gcount()` returns `-1` (the last unformatted input function `putback()` did "extract" back into the stream). Correspondingly for `unget()`. Is this what is intended? If so, this should be clarified. Otherwise, a corresponding clarification should be used.

Proposed resolution:

In 27.6.1.2.2 [lib.istream.formatted.arithmetic], paragraph 1. Change the beginning of the second sentence from "The conversion occurs" to "These extractors behave as formatted input functions (as described in 27.6.1.2.1). After a sentry object is constructed, the conversion occurs"

In 27.6.1.2.3, [lib.istream::extractors], before paragraph 1. Add an effects clause. "Effects: None. This extractor does not behave as a formatted input function (as described in 27.6.1.2.1).

In 27.6.1.2.3, [lib.istream::extractors], paragraph 2. Change the effects clause to "Effects: Calls pf(*this). This extractor does not behave as a formatted input function (as described in 27.6.1.2.1).

In 27.6.1.2.3, [lib.istream::extractors], paragraph 4. Change the effects clause to "Effects: Calls pf(*this). This extractor does not behave as a formatted input function (as described in 27.6.1.2.1).

In 27.6.1.2.3, [lib.istream::extractors], paragraph 12. Change the first two sentences from "If sb is null, calls setstate(failbit), which may throw ios_base::failure (27.4.4.3). Extracts characters from *this..." to "Behaves as a formatted input function (as described in 27.6.1.2.1). If sb is null, calls setstate(failbit), which may throw ios_base::failure (27.4.4.3). After a sentry object is constructed, extracts characters from *this...".

In 27.6.1.3, [lib.istream.unformatted], before paragraph 2. Add an effects clause. "Effects: none. This member function does not behave as an unformatted input function (as described in 27.6.1.3, paragraph 1)."

In 27.6.1.3, [lib.istream.unformatted], paragraph 3. Change the beginning of the first sentence of the effects clause from "Extracts a character" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts a character"

In 27.6.1.3, [lib.istream.unformatted], paragraph 5. Change the beginning of the first sentence of the effects clause from "Extracts a character" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts a character"

In 27.6.1.3, [lib.istream.unformatted], paragraph 7. Change the beginning of the first sentence of the effects clause from "Extracts characters" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts characters"

[No change needed in paragraph 10, because it refers to paragraph 7.]

In 27.6.1.3, [lib.istream.unformatted], paragraph 12. Change the beginning of the first sentence of the effects clause from "Extracts characters" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts characters"

[No change needed in paragraph 15.]

In 27.6.1.3, [lib.istream.unformatted], paragraph 17. Change the beginning of the first sentence of the effects clause from "Extracts characters" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts characters"

[No change needed in paragraph 23.]

In 27.6.1.3, [lib.istream.unformatted], paragraph 24. Change the beginning of the first sentence of the effects clause from "Extracts characters" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, extracts characters"

In 27.6.1.3, [lib.istream.unformatted], before paragraph 27. Add an Effects clause: "Effects: Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, reads but does not extract the current input character."

In 27.6.1.3, [lib.istream.unformatted], paragraph 28. Change the first sentence of the Effects clause from "If !good() calls" to Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, if !good() calls"

In 27.6.1.3, [lib.istream.unformatted], paragraph 30. Change the first sentence of the Effects clause from "If !good() calls" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, if !good() calls"

In 27.6.1.3, [lib.istream.unformatted], paragraph 32. Change the first sentence of the Effects clause from "If !good() calls..." to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, if !good() calls..." Add a new sentence to the end of the Effects clause: "[Note: this function extracts no characters, so the value returned by the next call to gcount() is 0.]"

In 27.6.1.3, [lib.istream.unformatted], paragraph 34. Change the first sentence of the Effects clause from "If !good() calls" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1). After constructing a sentry object, if !good() calls". Add a new sentence to the end of the Effects clause: "[Note: this function extracts no characters, so the value returned by the next call to gcount() is 0.]"

In 27.6.1.3, [lib.istream.unformatted], paragraph 36. Change the first sentence of the Effects clause from "If !rdbuf() is" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if rdbuf() is"

In 27.6.1.3, [lib.istream.unformatted], before paragraph 37. Add an Effects clause: "Effects: Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount()." Change the first sentence of paragraph 37 from "if fail()" to "after constructing a sentry object, if fail()".

In 27.6.1.3, [lib.istream.unformatted], paragraph 38. Change the first sentence of the Effects clause from "If fail()" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if fail()

In 27.6.1.3, [lib.istream.unformatted], paragraph 40. Change the first sentence of the Effects clause from "If fail()" to "Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if fail()

In 27.6.2.5.2 [lib.ostream.inserters.arithmetic], paragraph 1. Change the beginning of the third sentence from "The formatting conversion" to "These extractors behave as formatted output functions (as described in 27.6.2.5.1). After the sentry object is constructed, the conversion occurs".

In 27.6.2.5.3 [lib.ostream.inserters], before paragraph 1. Add an effects clause: "Effects: None. Does not behave as a formatted output function (as described in 27.6.2.5.1).".

In 27.6.2.5.3 [lib.ostream.inserters], paragraph 2. Change the effects clause to "Effects: calls pf(*this). This extractor does not behave as a formatted output function (as described in 27.6.2.5.1).".

In 27.6.2.5.3 [lib.ostream.inserters], paragraph 4. Change the effects clause to "Effects: calls pf(*this). This extractor does not behave as a formatted output function (as described in 27.6.2.5.1).".

In 27.6.2.5.3 [lib.ostream.inserters], paragraph 6. Change the first sentence from "If sb" to "Behaves as a formatted output function (as described in 27.6.2.5.1). After the sentry object is constructed, if sb".

In 27.6.2.6 [lib.ostream.unformatted], paragraph 2. Change the first sentence from "Inserts the character" to "Behaves as an unformatted output function (as described in 27.6.2.6, paragraph 1). After constructing a sentry object, inserts the character".

In 27.6.2.6 [lib.ostream.unformatted], paragraph 5. Change the first sentence from "Obtains characters" to "Behaves as an unformatted output function (as described in 27.6.2.6, paragraph 1). After constructing a sentry object, obtains characters".

In 27.6.2.6 [lib.ostream.unformatted], paragraph 7. Add a new sentence at the end of the paragraph: "Does not behave as an unformatted output function (as described in 27.6.2.6, paragraph 1)."

Rationale:

See J16/99-0043==WG21/N1219, Proposed Resolution to Library Issue 60, by Judy Ward and Matt Austern. This proposed resolution is section VI of that paper.

### 61. Ambiguity in iostreams exception policy

Section: 27.7.1.3 [istream.unformatted] Status: TC1 Submitter: Matt Austern Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The introduction to the section on unformatted input (27.6.1.3) says that every unformatted input function catches all exceptions that were thrown during input, sets badbit, and then conditionally rethrows the exception. That seems clear enough. Several of the specific functions, however, such as get() and read(), are documented in some circumstances as setting eofbit and/or failbit. (The standard notes, correctly, that setting eofbit or failbit can sometimes result in an exception being thrown.) The question: if one of these functions throws an exception triggered by setting failbit, is this an exception "thrown during input" and hence covered by 27.6.1.3, or does 27.6.1.3 only refer to a limited class of exceptions? Just to make this concrete, suppose you have the following snippet.

      char buffer[N];
      istream is;
      ...
      is.exceptions(istream::failbit); // Throw on failbit but not on badbit.
      is.read(buffer, N);

Now suppose we reach EOF before we've read N characters. What iostate bits can we expect to be set, and what exception (if any) will be thrown?

Proposed resolution:

In 27.6.1.3, paragraph 1, after the sentence that begins "If an exception is thrown...", add the following parenthetical comment: "(Exceptions thrown from `basic_ios<>::clear()` are not caught or rethrown.)"

Rationale:

The LWG looked to two alternative wordings, and choose the proposed resolution as better standardese.

### 62. `Sync`'s return value

Section: 27.7.1.3 [istream.unformatted] Status: TC1 Submitter: Matt Austern Opened: 1998-08-06 Last modified: 2008-09-26

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Discussion:

The Effects clause for sync() (27.6.1.3, paragraph 36) says that it "calls rdbuf()->pubsync() and, if that function returns -1 ... returns traits::eof()."

That looks suspicious, because traits::eof() is of type traits::int_type while the return type of sync() is int.

Proposed resolution:

In 27.7.1.3 [istream.unformatted], paragraph 36, change "returns `traits::eof()`" to "returns `-1`".

### 63. Exception-handling policy for unformatted output

Section: 27.7.2.7 [ostream.unformatted] Status: TC1 Submitter: Matt Austern Opened: 1998-08-11 Last modified: 2008-09-26

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Discussion:

Clause 27 details an exception-handling policy for formatted input, unformatted input, and formatted output. It says nothing for unformatted output (27.6.2.6). 27.6.2.6 should either include the same kind of exception-handling policy as in the other three places, or else it should have a footnote saying that the omission is deliberate.

Proposed resolution:

In 27.6.2.6, paragraph 1, replace the last sentence ("In any case, the unformatted output function ends by destroying the sentry object, then returning the value specified for the formatted output function.") with the following text:

> If an exception is thrown during output, then `ios::badbit` is turned on [Footnote: without causing an `ios::failure` to be thrown.] in `*this`'s error state. If `(exceptions() & badbit) != 0` then the exception is rethrown. In any case, the unformatted output function ends by destroying the sentry object, then, if no exception was thrown, returning the value specified for the formatted output function.

Rationale:

This exception-handling policy is consistent with that of formatted input, unformatted input, and formatted output.

### 64. Exception handling in `basic_istream::operator>>(basic_streambuf*)`

Section: 27.7.1.2.3 [istream::extractors] Status: TC1 Submitter: Matt Austern Opened: 1998-08-11 Last modified: 2008-09-26

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Discussion:

27.6.1.2.3, paragraph 13, is ambiguous. It can be interpreted two different ways, depending on whether the second sentence is read as an elaboration of the first.

Proposed resolution:

Replace 27.7.1.2.3 [istream::extractors], paragraph 13, which begins "If the function inserts no characters ..." with:

> If the function inserts no characters, it calls `setstate(failbit)`, which may throw `ios_base::failure` (27.4.4.3). If it inserted no characters because it caught an exception thrown while extracting characters from `sb` and `failbit` is on in `exceptions()` (27.4.4.3), then the caught exception is rethrown.

### 66. Strstreambuf::setbuf

Section: D.8.1.3 [depr.strstreambuf.virtuals] Status: TC1 Submitter: Matt Austern Opened: 1998-08-18 Last modified: 2008-09-26

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Discussion:

D.7.1.3, paragraph 19, says that strstreambuf::setbuf "Performs an operation that is defined separately for each class derived from strstreambuf". This is obviously an incorrect cut-and-paste from basic_streambuf. There are no classes derived from strstreambuf.

Proposed resolution:

D.8.1.3 [depr.strstreambuf.virtuals], paragraph 19, replace the setbuf effects clause which currently says "Performs an operation that is defined separately for each class derived from strstreambuf" with:

> Effects: implementation defined, except that `setbuf(0,0)` has no effect.

### 68. Extractors for char* should store null at end

Section: 27.7.1.2.3 [istream::extractors] Status: TC1 Submitter: Angelika Langer Opened: 1998-07-14 Last modified: 2008-09-26

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Discussion:

Extractors for char* (27.6.1.2.3) do not store a null character after the extracted character sequence whereas the unformatted functions like get() do. Why is this?

Comment from Jerry Schwarz: There is apparently an editing glitch. You'll notice that the last item of the list of what stops extraction doesn't make any sense. It was supposed to be the line that said a null is stored.

Proposed resolution:

27.7.1.2.3 [istream::extractors], paragraph 7, change the last list item from:

> A null byte (`charT()`) in the next position, which may be the first position if no characters were extracted.

to become a new paragraph which reads:

> Operator>> then stores a null byte (`charT()`) in the next position, which may be the first position if no characters were extracted.

### 69. Must elements of a vector be contiguous?

Section: 23.3.6 [vector] Status: TC1 Submitter: Andrew Koenig Opened: 1998-07-29 Last modified: 2008-09-26

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Discussion:

The issue is this: Must the elements of a vector be in contiguous memory?

(Please note that this is entirely separate from the question of whether a vector iterator is required to be a pointer; the answer to that question is clearly "no," as it would rule out debugging implementations)

Proposed resolution:

Add the following text to the end of 23.3.6 [vector], paragraph 1.

> The elements of a vector are stored contiguously, meaning that if v is a `vector<T, Allocator>` where T is some type other than `bool`, then it obeys the identity `&v[n] == &v[0] + n` for all `0 <= n < v.size()`.

Rationale:

The LWG feels that as a practical matter the answer is clearly "yes". There was considerable discussion as to the best way to express the concept of "contiguous", which is not directly defined in the standard. Discussion included:

- An operational definition similar to the above proposed resolution is already used for valarray (26.6.2.3 [valarray.access]).
- There is no need to explicitly consider a user-defined operator& because elements must be copyconstructible (23.2 [container.requirements] para 3) and copyconstructible (20.2.1 [utility.arg.requirements]) specifies requirements for operator&.
- There is no issue of one-past-the-end because of language rules.

### 70. Uncaught_exception() missing throw() specification

Section: 18.8 [support.exception], 18.8.4 [uncaught] Status: TC1 Submitter: Steve Clamage Opened: 1998-08-03 Last modified: 2008-09-26

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Discussion:

In article 3E04@pratique.fr, Valentin Bonnard writes:

uncaught_exception() doesn't have a throw specification.

It is intentional ? Does it means that one should be prepared to handle exceptions thrown from uncaught_exception() ?

uncaught_exception() is called in exception handling contexts where exception safety is very important.

Proposed resolution:

In 15.5.3 [except.uncaught], paragraph 1, 18.8 [support.exception], and 18.8.4 [uncaught], add "throw()" to uncaught_exception().

### 71. Do_get_monthname synopsis missing argument

Section: 22.4.5.1 [locale.time.get] Status: TC1 Submitter: Nathan Myers Opened: 1998-08-13 Last modified: 2008-09-26

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Discussion:

The locale facet member `time_get<>::do_get_monthname` is described in 22.4.5.1.2 [locale.time.get.virtuals] with five arguments, consistent with do_get_weekday and with its specified use by member get_monthname. However, in the synopsis, it is specified instead with four arguments. The missing argument is the "end" iterator value.

Proposed resolution:

In 22.4.5.1 [locale.time.get], add an "end" argument to the declaration of member do_monthname as follows:

      virtual iter_type do_get_monthname(iter_type s, iter_type end, ios_base&,
                                         ios_base::iostate& err, tm* t) const;

### 74. Garbled text for `codecvt::do_max_length`

Section: 22.4.1.4 [locale.codecvt] Status: TC1 Submitter: Matt Austern Opened: 1998-09-08 Last modified: 2008-09-26

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Discussion:

The text of `codecvt::do_max_length`'s "Returns" clause (22.2.1.5.2, paragraph 11) is garbled. It has unbalanced parentheses and a spurious n.

Proposed resolution:

Replace 22.4.1.4.2 [locale.codecvt.virtuals] paragraph 11 with the following:

> Returns: The maximum value that `do_length(state, from, from_end, 1)` can return for any valid range `[from, from_end)` and `stateT` value `state`. The specialization `codecvt<char, char, mbstate_t>::do_max_length()` returns 1.

### 75. Contradiction in `codecvt::length`'s argument types

Section: 22.4.1.4 [locale.codecvt] Status: TC1 Submitter: Matt Austern Opened: 1998-09-18 Last modified: 2008-09-26

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Discussion:

The class synopses for classes `codecvt<>` (22.2.1.5) and `codecvt_byname<>` (22.2.1.6) say that the first parameter of the member functions `length` and `do_length` is of type `const stateT&`. The member function descriptions, however (22.2.1.5.1, paragraph 6; 22.2.1.5.2, paragraph 9) say that the type is `stateT&`. Either the synopsis or the summary must be changed.

If (as I believe) the member function descriptions are correct, then we must also add text saying how `do_length` changes its `stateT` argument.

Proposed resolution:

In 22.4.1.4 [locale.codecvt], and also in 22.4.1.5 [locale.codecvt.byname], change the `stateT` argument type on both member `length()` and member `do_length()` from

> `const stateT&`

to

> `stateT&`

In 22.4.1.4.2 [locale.codecvt.virtuals], add to the definition for member `do_length` a paragraph:

> Effects: The effect on the `state` argument is ``as if'' it called `do_in(state, from, from_end, from, to, to+max, to)` for `to` pointing to a buffer of at least `max` elements.

### 76. Can a `codecvt` facet always convert one internal character at a time?

Section: 22.4.1.4 [locale.codecvt] Status: CD1 Submitter: Matt Austern Opened: 1998-09-25 Last modified: 2008-09-26

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Discussion:

This issue concerns the requirements on classes derived from `codecvt`, including user-defined classes. What are the restrictions on the conversion from external characters (e.g. `char`) to internal characters (e.g. `wchar_t`)? Or, alternatively, what assumptions about `codecvt` facets can the I/O library make?

The question is whether it's possible to convert from internal characters to external characters one internal character at a time, and whether, given a valid sequence of external characters, it's possible to pick off internal characters one at a time. Or, to put it differently: given a sequence of external characters and the corresponding sequence of internal characters, does a position in the internal sequence correspond to some position in the external sequence?

To make this concrete, suppose that `[first, last)` is a sequence of M external characters and that `[ifirst, ilast)` is the corresponding sequence of N internal characters, where N > 1. That is, `my_encoding.in()`, applied to `[first, last)`, yields `[ifirst, ilast)`. Now the question: does there necessarily exist a subsequence of external characters, `[first, last_1)`, such that the corresponding sequence of internal characters is the single character `*ifirst`?

(What a "no" answer would mean is that `my_encoding` translates sequences only as blocks. There's a sequence of M external characters that maps to a sequence of N internal characters, but that external sequence has no subsequence that maps to N-1 internal characters.)

Some of the wording in the standard, such as the description of `codecvt::do_max_length` (22.4.1.4.2 [locale.codecvt.virtuals], paragraph 11) and `basic_filebuf::underflow` (27.9.1.5 [filebuf.virtuals], paragraph 3) suggests that it must always be possible to pick off internal characters one at a time from a sequence of external characters. However, this is never explicitly stated one way or the other.

This issue seems (and is) quite technical, but it is important if we expect users to provide their own encoding facets. This is an area where the standard library calls user-supplied code, so a well-defined set of requirements for the user-supplied code is crucial. Users must be aware of the assumptions that the library makes. This issue affects positioning operations on `basic_filebuf`, unbuffered input, and several of `codecvt`'s member functions.

Proposed resolution:

Add the following text as a new paragraph, following 22.4.1.4.2 [locale.codecvt.virtuals] paragraph 2:

> A `codecvt` facet that is used by `basic_filebuf` (27.9 [file.streams]) must have the property that if

>         do_out(state, from, from_end, from_next, to, to_lim, to_next)

> would return `ok`, where `from != from_end`, then

>         do_out(state, from, from + 1, from_next, to, to_end, to_next)

> must also return `ok`, and that if

>         do_in(state, from, from_end, from_next, to, to_lim, to_next)

> would return `ok`, where `to != to_lim`, then

>         do_in(state, from, from_end, from_next, to, to + 1, to_next)

> must also return `ok`. [Footnote: Informally, this means that `basic_filebuf` assumes that the mapping from internal to external characters is 1 to N: a `codecvt` that is used by `basic_filebuf` must be able to translate characters one internal character at a time. --End Footnote]

[Redmond: Minor change in proposed resolution. Original proposed resolution talked about "success", with a parenthetical comment that success meant returning `ok`. New wording removes all talk about "success", and just talks about the return value.]

Rationale:

The proposed resoluion says that conversions can be performed one internal character at a time. This rules out some encodings that would otherwise be legal. The alternative answer would mean there would be some internal positions that do not correspond to any external file position.

An example of an encoding that this rules out is one where the `internT` and `externT` are of the same type, and where the internal sequence `c1 c2` corresponds to the external sequence `c2 c1`.

It was generally agreed that `basic_filebuf` relies on this property: it was designed under the assumption that the external-to-internal mapping is N-to-1, and it is not clear that `basic_filebuf` is implementable without that restriction.

The proposed resolution is expressed as a restriction on `codecvt` when used by `basic_filebuf`, rather than a blanket restriction on all `codecvt` facets, because `basic_filebuf` is the only other part of the library that uses `codecvt`. If a user wants to define a `codecvt` facet that implements a more general N-to-M mapping, there is no reason to prohibit it, so long as the user does not expect `basic_filebuf` to be able to use it.

### 78. Typo: event_call_back

Section: 27.5.2 [ios.base] Status: TC1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2008-09-26

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Discussion:

typo: event_call_back should be event_callback

Proposed resolution:

In the 27.5.2 [ios.base] synopsis change "event_call_back" to "event_callback".

### 79. Inconsistent declaration of polar()

Section: 26.4.1 [complex.syn], 26.4.7 [complex.value.ops] Status: TC1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2009-03-21

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Discussion:

In 26.4.1 [complex.syn] polar is declared as follows:

       template<class T> complex<T> polar(const T&, const T&);

In 26.4.7 [complex.value.ops] it is declared as follows:

       template<class T> complex<T> polar(const T& rho, const T& theta = 0);

Thus whether the second parameter is optional is not clear.

Proposed resolution:

In 26.4.1 [complex.syn] change:

       template<class T> complex<T> polar(const T&, const T&);

to:

       template<class T> complex<T> polar(const T& rho, const T& theta = 0);

### 80. Global Operators of complex declared twice

Section: 26.4.1 [complex.syn], 26.4.2 [complex] Status: TC1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2009-03-21

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Discussion:

Both 26.2.1 and 26.2.2 contain declarations of global operators for class complex. This redundancy should be removed.

Proposed resolution:

Reduce redundancy according to the general style of the standard.

### 83. String::npos vs. string::max_size()

Section: 21.4 [basic.string] Status: TC1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2008-09-26

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Duplicate of: 89

Discussion:

Many string member functions throw if size is getting or exceeding npos. However, I wonder why they don't throw if size is getting or exceeding max_size() instead of npos. May be npos is known at compile time, while max_size() is known at runtime. However, what happens if size exceeds max_size() but not npos, then? It seems the standard lacks some clarifications here.

Proposed resolution:

After 21.4 [basic.string] paragraph 4 ("The functions described in this clause...") add a new paragraph:

> For any string operation, if as a result of the operation, `size()` would exceed `max_size()` then the operation throws `length_error`.

Rationale:

The LWG believes length_error is the correct exception to throw.

### 86. String constructors don't describe exceptions

Section: 21.4.1 [string.require] Status: TC1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2008-09-26

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Discussion:

The constructor from a range:

    template<class InputIterator>
             basic_string(InputIterator begin, InputIterator end,
                          const Allocator& a = Allocator());

lacks a throws clause. However, I would expect that it throws according to the other constructors if the numbers of characters in the range equals npos (or exceeds max_size(), see above).

Proposed resolution:

In 21.4.1 [string.require], Strike throws paragraphs for constructors which say "Throws: length_error if n == npos."

Rationale:

Throws clauses for length_error if n == npos are no longer needed because they are subsumed by the general wording added by the resolution for issue 83.

### 90. Incorrect description of operator >> for strings

Section: 21.4.8.9 [string.io] Status: TC1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2008-09-26

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Discussion:

The effect of operator >> for strings contain the following item:

`isspace(c,getloc())` is true for the next available input character c.

Here `getloc()` has to be replaced by `is.getloc()`.

Proposed resolution:

In 21.4.8.9 [string.io] paragraph 1 Effects clause replace:

> `isspace(c,getloc())` is true for the next available input character c.

with:

> `isspace(c,is.getloc())` is true for the next available input character c.

### 91. Description of operator>> and getline() for string<> might cause endless loop

Section: 21.4.8.9 [string.io] Status: CD1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2008-09-26

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Discussion:

Operator >> and getline() for strings read until eof() in the input stream is true. However, this might never happen, if the stream can't read anymore without reaching EOF. So shouldn't it be changed into that it reads until !good() ?

Proposed resolution:

In 21.4.8.9 [string.io], paragraph 1, replace:

> Effects: Begins by constructing a sentry object k as if k were constructed by typename basic_istream<charT,traits>::sentry k( is). If bool( k) is true, it calls str.erase() and then extracts characters from is and appends them to str as if by calling str.append(1, c). If is.width() is greater than zero, the maximum number n of characters appended is is.width(); otherwise n is str.max_size(). Characters are extracted and appended until any of the following occurs:

with:

> Effects: Behaves as a formatted input function (27.7.1.2.1 [istream.formatted.reqmts]). After constructing a sentry object, if the sentry converts to true, calls str.erase() and then extracts characters from is and appends them to str as if by calling str.append(1,c). If is.width() is greater than zero, the maximum number n of characters appended is is.width(); otherwise n is str.max_size(). Characters are extracted and appended until any of the following occurs:

In 21.4.8.9 [string.io], paragraph 6, replace

> Effects: Begins by constructing a sentry object k as if by typename basic_istream<charT,traits>::sentry k( is, true). If bool( k) is true, it calls str.erase() and then extracts characters from is and appends them to str as if by calling str.append(1, c) until any of the following occurs:

with:

> Effects: Behaves as an unformatted input function (27.7.1.3 [istream.unformatted]), except that it does not affect the value returned by subsequent calls to basic_istream<>::gcount(). After constructing a sentry object, if the sentry converts to true, calls str.erase() and then extracts characters from is and appends them to str as if by calling str.append(1,c) until any of the following occurs:

[Redmond: Made changes in proposed resolution. `operator>>` should be a formatted input function, not an unformatted input function. `getline` should not be required to set `gcount`, since there is no mechanism for `gcount` to be set except by one of `basic_istream`'s member functions.]

[Curaçao: Nico agrees with proposed resolution.]

Rationale:

The real issue here is whether or not these string input functions get their characters from a streambuf, rather than by calling an istream's member functions, a streambuf signals failure either by returning eof or by throwing an exception; there are no other possibilities. The proposed resolution makes it clear that these two functions do get characters from a streambuf.

### 92. Incomplete Algorithm Requirements

Section: 25 [algorithms] Status: CD1 Submitter: Nico Josuttis Opened: 1998-09-29 Last modified: 2008-09-26

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Discussion:

The standard does not state, how often a function object is copied, called, or the order of calls inside an algorithm. This may lead to surprising/buggy behavior. Consider the following example:

    class Nth {    // function object that returns true for the nth element
      private:
        int nth;     // element to return true for
        int count;   // element counter
      public:
        Nth (int n) : nth(n), count(0) {
        }
        bool operator() (int) {
            return ++count == nth;
        }
    };
    ....
    // remove third element
        list<int>::iterator pos;
        pos = remove_if(coll.begin(),coll.end(),  // range
                        Nth(3)),                  // remove criterion
        coll.erase(pos,coll.end());

This call, in fact removes the 3rd AND the 6th element. This happens because the usual implementation of the algorithm copies the function object internally:

    template <class ForwIter, class Predicate>
    ForwIter std::remove_if(ForwIter beg, ForwIter end, Predicate op)
    {
        beg = find_if(beg, end, op);
        if (beg == end) {
            return beg;
        }
        else {
            ForwIter next = beg;
            return remove_copy_if(++next, end, beg, op);
        }
    }

The algorithm uses find_if() to find the first element that should be removed. However, it then uses a copy of the passed function object to process the resulting elements (if any). Here, Nth is used again and removes also the sixth element. This behavior compromises the advantage of function objects being able to have a state. Without any cost it could be avoided (just implement it directly instead of calling find_if()).

Proposed resolution:

Add a new paragraph following 25 [algorithms] paragraph 8:

> [Note: Unless otherwise specified, algorithms that take function objects as arguments are permitted to copy those function objects freely. Programmers for whom object identity is important should consider using a wrapper class that points to a noncopied implementation object, or some equivalent solution.]

[Dublin: Pete Becker felt that this may not be a defect, but rather something that programmers need to be educated about. There was discussion of adding wording to the effect that the number and order of calls to function objects, including predicates, not affect the behavior of the function object.]

[Pre-Kona: Nico comments: It seems the problem is that we don't have a clear statement of "predicate" in the standard. People including me seemed to think "a function returning a Boolean value and being able to be called by an STL algorithm or be used as sorting criterion or ... is a predicate". But a predicate has more requirements: It should never change its behavior due to a call or being copied. IMHO we have to state this in the standard. If you like, see section 8.1.4 of my library book for a detailed discussion.]

[Kona: Nico will provide wording to the effect that "unless otherwise specified, the number of copies of and calls to function objects by algorithms is unspecified". Consider placing in 25 [algorithms] after paragraph 9.]

[Santa Cruz: The standard doesn't currently guarantee that functions object won't be copied, and what isn't forbidden is allowed. It is believed (especially since implementations that were written in concert with the standard do make copies of function objects) that this was intentional. Thus, no normative change is needed. What we should put in is a non-normative note suggesting to programmers that if they want to guarantee the lack of copying they should use something like the `ref` wrapper.]

[Oxford: Matt provided wording.]

### 98. Input iterator requirements are badly written

Section: 24.2.1 [input.iterators] Status: CD1 Submitter: AFNOR Opened: 1998-10-07 Last modified: 2008-09-26

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Discussion:

Table 72 in 24.2.1 [input.iterators] specifies semantics for `*r++` of:

`{ T tmp = *r; ++r; return tmp; }`

There are two problems with this. First, the return type is specified to be "T", as opposed to something like "convertible to T". This is too specific: we want to allow *r++ to return an lvalue.

Second, writing the semantics in terms of code misleadingly suggests that the effects *r++ should precisely replicate the behavior of this code, including side effects. (Does this mean that *r++ should invoke the copy constructor exactly as many times as the sample code above would?) See issue 334 for a similar problem.

Proposed resolution:

In Table 72 in 24.2.1 [input.iterators], change the return type for `*r++` from `T` to "convertible to T".

Rationale:

This issue has two parts: the return type, and the number of times the copy constructor is invoked.

The LWG believes the the first part is a real issue. It's inappropriate for the return type to be specified so much more precisely for *r++ than it is for *r. In particular, if r is of (say) type `int*`, then *r++ isn't `int`, but `int&`.

The LWG does not believe that the number of times the copy constructor is invoked is a real issue. This can vary in any case, because of language rules on copy constructor elision. That's too much to read into these semantics clauses.

Additionally, as Dave Abrahams pointed out (c++std-lib-13703): since we're told (24.1/3) that forward iterators satisfy all the requirements of input iterators, we can't impose any requirements in the Input Iterator requirements table that forward iterators don't satisfy.

### 103. set::iterator is required to be modifiable, but this allows modification of keys

Section: 23.2.4 [associative.reqmts] Status: CD1 Submitter: AFNOR Opened: 1998-10-07 Last modified: 2008-09-26

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Discussion:

Set::iterator is described as implementation-defined with a reference to the container requirement; the container requirement says that const_iterator is an iterator pointing to const T and iterator an iterator pointing to T.

23.1.2 paragraph 2 implies that the keys should not be modified to break the ordering of elements. But that is not clearly specified. Especially considering that the current standard requires that iterator for associative containers be different from const_iterator. Set, for example, has the following:

`typedef implementation defined iterator;
// See _lib.container.requirements_`

23.2 [container.requirements] actually requires that iterator type pointing to T (table 65). Disallowing user modification of keys by changing the standard to require an iterator for associative container to be the same as const_iterator would be overkill since that will unnecessarily significantly restrict the usage of associative container. A class to be used as elements of set, for example, can no longer be modified easily without either redesigning the class (using mutable on fields that have nothing to do with ordering), or using const_cast, which defeats requiring iterator to be const_iterator. The proposed solution goes in line with trusting user knows what he is doing.

Other Options Evaluated:

Option A. In 23.2.4 [associative.reqmts], paragraph 2, after first sentence, and before "In addition,...", add one line:

> Modification of keys shall not change their strict weak ordering.

Option B. Add three new sentences to 23.2.4 [associative.reqmts]:

> At the end of paragraph 5: "Keys in an associative container are immutable." At the end of paragraph 6: "For associative containers where the value type is the same as the key type, both `iterator` and `const_iterator` are constant iterators. It is unspecified whether or not `iterator` and `const_iterator` are the same type."

Option C. To 23.2.4 [associative.reqmts], paragraph 3, which currently reads:

> The phrase ``equivalence of keys'' means the equivalence relation imposed by the comparison and not the operator== on keys. That is, two keys k1 and k2 in the same container are considered to be equivalent if for the comparison object comp, comp(k1, k2) == false && comp(k2, k1) == false.

add the following:

> For any two keys k1 and k2 in the same container, comp(k1, k2) shall return the same value whenever it is evaluated. [Note: If k2 is removed from the container and later reinserted, comp(k1, k2) must still return a consistent value but this value may be different than it was the first time k1 and k2 were in the same container. This is intended to allow usage like a string key that contains a filename, where comp compares file contents; if k2 is removed, the file is changed, and the same k2 (filename) is reinserted, comp(k1, k2) must again return a consistent value but this value may be different than it was the previous time k2 was in the container.]

Proposed resolution:

Add the following to 23.2.4 [associative.reqmts] at the indicated location:

> At the end of paragraph 3: "For any two keys k1 and k2 in the same container, calling comp(k1, k2) shall always return the same value."

> At the end of paragraph 5: "Keys in an associative container are immutable."

> At the end of paragraph 6: "For associative containers where the value type is the same as the key type, both `iterator` and `const_iterator` are constant iterators. It is unspecified whether or not `iterator` and `const_iterator` are the same type."

Rationale:

Several arguments were advanced for and against allowing set elements to be mutable as long as the ordering was not effected. The argument which swayed the LWG was one of safety; if elements were mutable, there would be no compile-time way to detect of a simple user oversight which caused ordering to be modified. There was a report that this had actually happened in practice, and had been painful to diagnose. If users need to modify elements, it is possible to use mutable members or const_cast.

Simply requiring that keys be immutable is not sufficient, because the comparison object may indirectly (via pointers) operate on values outside of the keys.

The types `iterator` and `const_iterator` are permitted to be different types to allow for potential future work in which some member functions might be overloaded between the two types. No such member functions exist now, and the LWG believes that user functionality will not be impaired by permitting the two types to be the same. A function that operates on both iterator types can be defined for `const_iterator` alone, and can rely on the automatic conversion from `iterator` to `const_iterator`.

[Tokyo: The LWG crafted the proposed resolution and rationale.]

### 106. Numeric library private members are implementation defined

Section: 26.6.5 [template.slice.array] Status: TC1 Submitter: AFNOR Opened: 1998-10-07 Last modified: 2008-09-26

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Discussion:

This is the only place in the whole standard where the implementation has to document something private.

Proposed resolution:

Remove the comment which says "// remainder implementation defined" from:

- 26.6.5 [template.slice.array]
- 26.6.7 [template.gslice.array]
- 26.6.8 [template.mask.array]
- 26.6.9 [template.indirect.array]

### 108. Lifetime of exception::what() return unspecified

Section: 18.7.1 [type.info] Status: TC1 Submitter: AFNOR Opened: 1998-10-07 Last modified: 2008-09-26

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Discussion:

In 18.6.1, paragraphs 8-9, the lifetime of the return value of exception::what() is left unspecified. This issue has implications with exception safety of exception handling: some exceptions should not throw bad_alloc.

Proposed resolution:

Add to 18.7.1 [type.info] paragraph 9 (exception::what notes clause) the sentence:

> The return value remains valid until the exception object from which it is obtained is destroyed or a non-const member function of the exception object is called.

Rationale:

If an exception object has non-const members, they may be used to set internal state that should affect the contents of the string returned by `what()`.

### 109. Missing binders for non-const sequence elements

Section: D.9 [depr.lib.binders] Status: CD1 Submitter: Bjarne Stroustrup Opened: 1998-10-07 Last modified: 2008-09-26

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Discussion:

There are no versions of binders that apply to non-const elements of a sequence. This makes examples like for_each() using bind2nd() on page 521 of "The C++ Programming Language (3rd)" non-conforming. Suitable versions of the binders need to be added.

Further discussion from Nico:

What is probably meant here is shown in the following example:

    class Elem {
      public:
        void print (int i) const { }
        void modify (int i) { }
    };

    int main()
    {
        vector<Elem> coll(2);
        for_each (coll.begin(), coll.end(), bind2nd(mem_fun_ref(&Elem::print),42));    // OK
        for_each (coll.begin(), coll.end(), bind2nd(mem_fun_ref(&Elem::modify),42));   // ERROR
    }

The error results from the fact that bind2nd() passes its first argument (the argument of the sequence) as constant reference. See the following typical implementation:

>     template <class Operation>
>     class binder2nd
>       : public unary_function<typename Operation::first_argument_type,
>                               typename Operation::result_type> {
>     protected:
>       Operation op;
>       typename Operation::second_argument_type value;
>     public:
>       binder2nd(const Operation& o,
>                 const typename Operation::second_argument_type& v)
>           : op(o), value(v) {}

>      typename Operation::result_type
>       operator()(const typename Operation::first_argument_type& x) const {
>         return op(x, value);
>       }
>     };

The solution is to overload operator () of bind2nd for non-constant arguments:

>     template <class Operation>
>     class binder2nd
>       : public unary_function<typename Operation::first_argument_type,
>                               typename Operation::result_type> {
>     protected:
>       Operation op;
>       typename Operation::second_argument_type value;
>     public:
>       binder2nd(const Operation& o,
>                 const typename Operation::second_argument_type& v)
>           : op(o), value(v) {}

>      typename Operation::result_type
>       operator()(const typename Operation::first_argument_type& x) const {
>         return op(x, value);
>       }
>       typename Operation::result_type
>       operator()(typename Operation::first_argument_type& x) const {
>         return op(x, value);
>       }
>     };

Proposed resolution:

Howard believes there is a flaw in this resolution. See c++std-lib-9127. We may need to reopen this issue.

In D.9 [depr.lib.binders] in the declaration of binder1st after:

> `typename Operation::result_type
> operator()(const typename Operation::second_argument_type& x) const;`

insert:

> `typename Operation::result_type
> operator()(typename Operation::second_argument_type& x) const;`

In D.9 [depr.lib.binders] in the declaration of binder2nd after:

> `typename Operation::result_type
> operator()(const typename Operation::first_argument_type& x) const;`

insert:

> `typename Operation::result_type
> operator()(typename Operation::first_argument_type& x) const;`

[Kona: The LWG discussed this at some length.It was agreed that this is a mistake in the design, but there was no consensus on whether it was a defect in the Standard. Straw vote: NAD - 5. Accept proposed resolution - 3. Leave open - 6.]

[Copenhagen: It was generally agreed that this was a defect. Strap poll: NAD - 0. Accept proposed resolution - 10. Leave open - 1.]

### 110. istreambuf_iterator::equal not const

Section: 24.6.3 [istreambuf.iterator], 24.6.3.5 [istreambuf.iterator::equal] Status: TC1 Submitter: Nathan Myers Opened: 1998-10-15 Last modified: 2008-09-26

View all other issues in [istreambuf.iterator].

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Discussion:

Member istreambuf_iterator<>::equal is not declared "const", yet 24.6.3.6 [istreambuf.iterator::op==] says that operator==, which is const, calls it. This is contradictory.

Proposed resolution:

In 24.6.3 [istreambuf.iterator] and also in 24.6.3.5 [istreambuf.iterator::equal], replace:

>     bool equal(istreambuf_iterator& b);

with:

>     bool equal(const istreambuf_iterator& b) const;

### 112. Minor typo in `ostreambuf_iterator` constructor

Section: 24.6.4.1 [ostreambuf.iter.cons] Status: TC1 Submitter: Matt Austern Opened: 1998-10-20 Last modified: 2008-09-26

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Discussion:

The requires clause for `ostreambuf_iterator`'s constructor from an `ostream_type` (24.5.4.1, paragraph 1) reads "s is not null". However, s is a reference, and references can't be null.

Proposed resolution:

In 24.6.4.1 [ostreambuf.iter.cons]:

Move the current paragraph 1, which reads "Requires: s is not null.", from the first constructor to the second constructor.

Insert a new paragraph 1 Requires clause for the first constructor reading:

> Requires: `s.rdbuf()` is not null.

### 114. Placement forms example in error twice

Section: 18.6.1.3 [new.delete.placement] Status: TC1 Submitter: Steve Clamage Opened: 1998-10-28 Last modified: 2008-09-26

View all other issues in [new.delete.placement].

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Duplicate of: 196

Discussion:

Section 18.5.1.3 contains the following example:

    [Example: This can be useful for constructing an object at a known address:
            char place[sizeof(Something)];
            Something* p = new (place) Something();
     -end example]

First code line: "place" need not have any special alignment, and the following constructor could fail due to misaligned data.

Second code line: Aren't the parens on Something() incorrect? [Dublin: the LWG believes the () are correct.]

Examples are not normative, but nevertheless should not show code that is invalid or likely to fail.

Proposed resolution:

Replace the first line of code in the example in 18.6.1.3 [new.delete.placement] with:

>     void* place = operator new(sizeof(Something));

### 115. Typo in strstream constructors

Section: D.8.4.1 [depr.strstream.cons] Status: TC1 Submitter: Steve Clamage Opened: 1998-11-02 Last modified: 2008-09-26

View all issues with TC1 status.

Discussion:

D.7.4.1 strstream constructors paragraph 2 says:

> Effects: Constructs an object of class strstream, initializing the base class with iostream(& sb) and initializing sb with one of the two constructors:

> - If mode&app==0, then s shall designate the first element of an array of n elements. The constructor is strstreambuf(s, n, s).

> - If mode&app==0, then s shall designate the first element of an array of n elements that contains an NTBS whose first element is designated by s. The constructor is strstreambuf(s, n, s+std::strlen(s)).

Notice the second condition is the same as the first. I think the second condition should be "If mode&app==app", or "mode&app!=0", meaning that the append bit is set.

Proposed resolution:

In D.8.3.1 [depr.ostrstream.cons] paragraph 2 and D.8.4.1 [depr.strstream.cons] paragraph 2, change the first condition to `(mode&app)==0` and the second condition to `(mode&app)!=0`.

### 117. `basic_ostream` uses nonexistent `num_put` member functions

Section: 27.7.2.6.2 [ostream.inserters.arithmetic] Status: CD1 Submitter: Matt Austern Opened: 1998-11-20 Last modified: 2008-09-26

View all other issues in [ostream.inserters.arithmetic].

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Discussion:

The effects clause for numeric inserters says that insertion of a value `x`, whose type is either `bool`, `short`, `unsigned short`, `int`, `unsigned int`, `long`, `unsigned long`, `float`, `double`, `long double`, or `const void*`, is delegated to `num_put`, and that insertion is performed as if through the following code fragment:

    bool failed = use_facet<
       num_put<charT,ostreambuf_iterator<charT,traits> >
       >(getloc()).put(*this, *this, fill(), val). failed();

This doesn't work, because `num_put<>`::put is only overloaded for the types `bool`, `long`, `unsigned long`, `double`, `long double`, and `const void*`. That is, the code fragment in the standard is incorrect (it is diagnosed as ambiguous at compile time) for the types `short`, `unsigned short`, `int`, `unsigned int`, and `float`.

We must either add new member functions to `num_put`, or else change the description in `ostream` so that it only calls functions that are actually there. I prefer the latter.

Proposed resolution:

Replace 27.6.2.5.2, paragraph 1 with the following:

> The classes num_get<> and num_put<> handle locale-dependent numeric formatting and parsing. These inserter functions use the imbued locale value to perform numeric formatting. When val is of type bool, long, unsigned long, double, long double, or const void*, the formatting conversion occurs as if it performed the following code fragment:

>     bool failed = use_facet<
>        num_put<charT,ostreambuf_iterator<charT,traits> >
>        >(getloc()).put(*this, *this, fill(), val). failed();

> When val is of type short the formatting conversion occurs as if it performed the following code fragment:

>     ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
>     bool failed = use_facet<
>        num_put<charT,ostreambuf_iterator<charT,traits> >
>        >(getloc()).put(*this, *this, fill(),
>           baseflags == ios_base::oct || baseflags == ios_base::hex
>              ? static_cast<long>(static_cast<unsigned short>(val))
>              : static_cast<long>(val)). failed();

> When val is of type int the formatting conversion occurs as if it performed the following code fragment:

>     ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
>     bool failed = use_facet<
>        num_put<charT,ostreambuf_iterator<charT,traits> >
>        >(getloc()).put(*this, *this, fill(),
>           baseflags == ios_base::oct || baseflags == ios_base::hex
>              ? static_cast<long>(static_cast<unsigned int>(val))
>              : static_cast<long>(val)). failed();

> When val is of type unsigned short or unsigned int the formatting conversion occurs as if it performed the following code fragment:

>     bool failed = use_facet<
>        num_put<charT,ostreambuf_iterator<charT,traits> >
>        >(getloc()).put(*this, *this, fill(), static_cast<unsigned long>(val)).
>     failed();

> When val is of type float the formatting conversion occurs as if it performed the following code fragment:

>     bool failed = use_facet<
>        num_put<charT,ostreambuf_iterator<charT,traits> >
>        >(getloc()).put(*this, *this, fill(), static_cast<double>(val)).
>     failed();

[post-Toronto: This differs from the previous proposed resolution; PJP provided the new wording. The differences are in signed short and int output.]

Rationale:

The original proposed resolution was to cast int and short to long, unsigned int and unsigned short to unsigned long, and float to double, thus ensuring that we don't try to use nonexistent num_put<> member functions. The current proposed resolution is more complicated, but gives more expected results for hex and octal output of signed short and signed int. (On a system with 16-bit short, for example, printing short(-1) in hex format should yield 0xffff.)

### 118. `basic_istream` uses nonexistent `num_get` member functions

Section: 27.7.1.2.2 [istream.formatted.arithmetic] Status: CD1 Submitter: Matt Austern Opened: 1998-11-20 Last modified: 2008-09-26

View all other issues in [istream.formatted.arithmetic].

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Discussion:

Formatted input is defined for the types `short`, `unsigned short`, `int`, `unsigned int`, `long`, `unsigned long`, `float`, `double`, `long double`, `bool`, and `void*`. According to section 27.6.1.2.2, formatted input of a value `x` is done as if by the following code fragment:

    typedef num_get< charT,istreambuf_iterator<charT,traits> > numget;
    iostate err = 0;
    use_facet< numget >(loc).get(*this, 0, *this, err, val);
    setstate(err);

According to section 22.4.2.1.1 [facet.num.get.members], however, `num_get<>::get()` is only overloaded for the types `bool`, `long`, `unsigned short`, `unsigned int`, `unsigned long`, `unsigned long`, `float`, `double`, `long double`, and `void*`. Comparing the lists from the two sections, we find that 27.6.1.2.2 is using a nonexistent function for types `short` and `int`.

Proposed resolution:

In 27.7.1.2.2 [istream.formatted.arithmetic] Arithmetic Extractors, remove the two lines (1st and 3rd) which read:

>     operator>>(short& val);
>     ...
>     operator>>(int& val);

And add the following at the end of that section (27.6.1.2.2) :

>     operator>>(short& val);

> The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):

>       typedef num_get< charT,istreambuf_iterator<charT,traits> > numget;
>       iostate err = 0;
>       long lval;
>       use_facet< numget >(loc).get(*this, 0, *this, err, lval);
>             if (err == 0
>                     && (lval < numeric_limits<short>::min() || numeric_limits<short>::max() < lval))
>                     err = ios_base::failbit;
>       setstate(err);

>     operator>>(int& val);

> The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):

>       typedef num_get< charT,istreambuf_iterator<charT,traits> > numget;
>       iostate err = 0;
>       long lval;
>       use_facet< numget >(loc).get(*this, 0, *this, err, lval);
>             if (err == 0
>                     && (lval < numeric_limits<int>::min() || numeric_limits<int>::max() < lval))
>                     err = ios_base::failbit;
>       setstate(err);

[Post-Tokyo: PJP provided the above wording.]

### 119. Should virtual functions be allowed to strengthen the exception specification?

Section: 17.6.4.11 [res.on.exception.handling] Status: TC1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2008-09-26

View all other issues in [res.on.exception.handling].

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Discussion:

Section 17.6.4.11 [res.on.exception.handling] states:

"An implementation may strengthen the exception-specification for a function by removing listed exceptions."

The problem is that if an implementation is allowed to do this for virtual functions, then a library user cannot write a class that portably derives from that class.

For example, this would not compile if ios_base::failure::~failure had an empty exception specification:

    #include <ios>
    #include <string>

    class D : public std::ios_base::failure {
    public:
            D(const std::string&);
            ~D(); // error - exception specification must be compatible with
                  // overridden virtual function ios_base::failure::~failure()
    };

Proposed resolution:

Change Section 17.6.4.11 [res.on.exception.handling] from:

"may strengthen the exception-specification for a function"

to:

"may strengthen the exception-specification for a non-virtual function".

### 120. Can an implementor add specializations?

Section: 17.6.3.3 [reserved.names] Status: CD1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2008-09-26

View all other issues in [reserved.names].

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Discussion:

The original issue asked whether a library implementor could specialize standard library templates for built-in types. (This was an issue because users are permitted to explicitly instantiate standard library templates.)

Specializations are no longer a problem, because of the resolution to core issue 259. Under the proposed resolution, it will be legal for a translation unit to contain both a specialization and an explicit instantiation of the same template, provided that the specialization comes first. In such a case, the explicit instantiation will be ignored. Further discussion of library issue 120 assumes that the core 259 resolution will be adopted.

However, as noted in lib-7047, one piece of this issue still remains: what happens if a standard library implementor explicitly instantiates a standard library templates? It's illegal for a program to contain two different explicit instantiations of the same template for the same type in two different translation units (ODR violation), and the core working group doesn't believe it is practical to relax that restriction.

The issue, then, is: are users allowed to explicitly instantiate standard library templates for non-user defined types? The status quo answer is 'yes'. Changing it to 'no' would give library implementors more freedom.

This is an issue because, for performance reasons, library implementors often need to explicitly instantiate standard library templates. (for example, std::basic_string<char>) Does giving users freedom to explicitly instantiate standard library templates for non-user defined types make it impossible or painfully difficult for library implementors to do this?

John Spicer suggests, in lib-8957, that library implementors have a mechanism they can use for explicit instantiations that doesn't prevent users from performing their own explicit instantiations: put each explicit instantiation in its own object file. (Different solutions might be necessary for Unix DSOs or MS-Windows DLLs.) On some platforms, library implementors might not need to do anything special: the "undefined behavior" that results from having two different explicit instantiations might be harmless.

Proposed resolution:

Append to 17.6.3.3 [reserved.names] paragraph 1:

> A program may explicitly instantiate any templates in the standard library only if the declaration depends on the name of a user-defined type of external linkage and the instantiation meets the standard library requirements for the original template.

[Kona: changed the wording from "a user-defined name" to "the name of a user-defined type"]

Rationale:

The LWG considered another possible resolution:

> In light of the resolution to core issue 259, no normative changes in the library clauses are necessary. Add the following non-normative note to the end of 17.6.3.3 [reserved.names] paragraph 1:

> > [Note: A program may explicitly instantiate standard library templates, even when an explicit instantiation does not depend on a user-defined name. --end note]

The LWG rejected this because it was believed that it would make it unnecessarily difficult for library implementors to write high-quality implementations. A program may not include an explicit instantiation of the same template, for the same template arguments, in two different translation units. If users are allowed to provide explicit instantiations of Standard Library templates for built-in types, then library implementors aren't, at least not without nonportable tricks.

The most serious problem is a class template that has writeable static member variables. Unfortunately, such class templates are important and, in existing Standard Library implementations, are often explicitly specialized by library implementors: locale facets, which have a writeable static member variable `id`. If a user's explicit instantiation collided with the implementations explicit instantiation, iostream initialization could cause locales to be constructed in an inconsistent state.

One proposed implementation technique was for Standard Library implementors to provide explicit instantiations in separate object files, so that they would not be picked up by the linker when the user also provides an explicit instantiation. However, this technique only applies for Standard Library implementations that are packaged as static archives. Most Standard Library implementations nowadays are packaged as dynamic libraries, so this technique would not apply.

The Committee is now considering standardization of dynamic linking. If there are such changes in the future, it may be appropriate to revisit this issue later.

### 122. streambuf/wstreambuf description should not say they are specializations

Section: 27.6.2 [streambuf] Status: TC1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2008-09-26

View all other issues in [streambuf].

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Discussion:

Section 27.5.2 describes the streambuf classes this way:

> The class streambuf is a specialization of the template class basic_streambuf specialized for the type char.

> The class wstreambuf is a specialization of the template class basic_streambuf specialized for the type wchar_t.

This implies that these classes must be template specializations, not typedefs.

It doesn't seem this was intended, since Section 27.5 has them declared as typedefs.

Proposed resolution:

Remove 27.6.2 [streambuf] paragraphs 2 and 3 (the above two sentences).

Rationale:

The `streambuf` synopsis already has a declaration for the typedefs and that is sufficient.

### 123. Should valarray helper arrays fill functions be const?

Section: 26.6.5.3 [slice.arr.fill], 26.6.7.3 [gslice.array.fill], 26.6.8.3 [mask.array.fill], 26.6.9.3 [indirect.array.fill] Status: CD1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2008-09-26

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Discussion:

One of the operator= in the valarray helper arrays is const and one is not. For example, look at slice_array. This operator= in Section 26.6.5.1 [slice.arr.assign] is const:

`void operator=(const valarray<T>&) const;`

but this one in Section 26.6.5.3 [slice.arr.fill] is not:

`void operator=(const T&);`

The description of the semantics for these two functions is similar.

Proposed resolution:

26.6.5 [template.slice.array] Template class slice_array

> In the class template definition for slice_array, replace the member function declaration

>           void operator=(const T&);

> with

>           void operator=(const T&) const;

26.6.5.3 [slice.arr.fill] slice_array fill function

> Change the function declaration

>           void operator=(const T&);

> to

>           void operator=(const T&) const;

26.6.7 [template.gslice.array] Template class gslice_array

> In the class template definition for gslice_array, replace the member function declaration

>           void operator=(const T&);

> with

>           void operator=(const T&) const;

26.6.7.3 [gslice.array.fill] gslice_array fill function

> Change the function declaration

>           void operator=(const T&);

> to

>           void operator=(const T&) const;

26.6.8 [template.mask.array] Template class mask_array

> In the class template definition for mask_array, replace the member function declaration

>           void operator=(const T&);

> with

>           void operator=(const T&) const;

26.6.8.3 [mask.array.fill] mask_array fill function

> Change the function declaration

>           void operator=(const T&);

> to

>           void operator=(const T&) const;

26.6.9 [template.indirect.array] Template class indirect_array

> In the class template definition for indirect_array, replace the member function declaration

>           void operator=(const T&);

> with

>           void operator=(const T&) const;

26.6.9.3 [indirect.array.fill] indirect_array fill function

> Change the function declaration

>           void operator=(const T&);

> to

>           void operator=(const T&) const;

[Redmond: Robert provided wording.]

Rationale:

There's no good reason for one version of operator= being const and another one not. Because of issue 253, this now matters: these functions are now callable in more circumstances. In many existing implementations, both versions are already const.

### 124. ctype_byname<charT>::do_scan_is & do_scan_not return type should be const charT*

Section: 22.4.1.2 [locale.ctype.byname] Status: TC1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2008-09-26

View all other issues in [locale.ctype.byname].

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Discussion:

In Section 22.4.1.2 [locale.ctype.byname] ctype_byname<charT>::do_scan_is() and do_scan_not() are declared to return a const char* not a const charT*.

Proposed resolution:

Change Section 22.4.1.2 [locale.ctype.byname] `do_scan_is()` and `do_scan_not()` to return a `const charT*`.

### 125. valarray<T>::operator!() return type is inconsistent

Section: 26.6.2 [template.valarray] Status: TC1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2008-09-26

View all other issues in [template.valarray].

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Discussion:

In Section 26.6.2 [template.valarray] valarray<T>::operator!() is declared to return a valarray<T>, but in Section 26.6.2.5 [valarray.unary] it is declared to return a valarray<bool>. The latter appears to be correct.

Proposed resolution:

Change in Section 26.6.2 [template.valarray] the declaration of `operator!()` so that the return type is `valarray<bool>`.

### 126. typos in Effects clause of ctype::do_narrow()

Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: TC1 Submitter: Judy Ward Opened: 1998-12-15 Last modified: 2008-09-26

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Discussion:

Typos in 22.2.1.1.2 need to be fixed.

Proposed resolution:

In Section 22.4.1.1.2 [locale.ctype.virtuals] change:

       do_widen(do_narrow(c),0) == c

to:

       do_widen(do_narrow(c,0)) == c

and change:

       (is(M,c) || !ctc.is(M, do_narrow(c),dfault) )

to:

       (is(M,c) || !ctc.is(M, do_narrow(c,dfault)) )

### 127. auto_ptr<> conversion issues

Section: D.10.1 [auto.ptr] Status: TC1 Submitter: Greg Colvin Opened: 1999-02-17 Last modified: 2008-09-26

View all other issues in [auto.ptr].

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Discussion:

There are two problems with the current `auto_ptr` wording in the standard:

First, the `auto_ptr_ref` definition cannot be nested because `auto_ptr<Derived>::auto_ptr_ref` is unrelated to `auto_ptr<Base>::auto_ptr_ref`. Also submitted by Nathan Myers, with the same proposed resolution.

Second, there is no `auto_ptr` assignment operator taking an `auto_ptr_ref` argument.

I have discussed these problems with my proposal coauthor, Bill Gibbons, and with some compiler and library implementors, and we believe that these problems are not desired or desirable implications of the standard.

25 Aug 1999: The proposed resolution now reflects changes suggested by Dave Abrahams, with Greg Colvin's concurrence; 1) changed "assignment operator" to "public assignment operator", 2) changed effects to specify use of release(), 3) made the conversion to auto_ptr_ref const.

2 Feb 2000: Lisa Lippincott comments: [The resolution of] this issue states that the conversion from auto_ptr to auto_ptr_ref should be const. This is not acceptable, because it would allow initialization and assignment from _any_ const auto_ptr! It also introduces an implementation difficulty in writing this conversion function -- namely, somewhere along the line, a const_cast will be necessary to remove that const so that release() may be called. This may result in undefined behavior [7.1.5.1/4]. The conversion operator does not have to be const, because a non-const implicit object parameter may be bound to an rvalue [13.3.3.1.4/3] [13.3.1/5].

Tokyo: The LWG removed the following from the proposed resolution:

In 20.6.4 [meta.unary], paragraph 2, and 20.6.4.3 [meta.unary.prop], paragraph 2, make the conversion to auto_ptr_ref const:

>     template<class Y> operator auto_ptr_ref<Y>() const throw();

Proposed resolution:

In 20.6.4 [meta.unary], paragraph 2, move the `auto_ptr_ref` definition to namespace scope.

In 20.6.4 [meta.unary], paragraph 2, add a public assignment operator to the `auto_ptr` definition:

>     auto_ptr& operator=(auto_ptr_ref<X> r) throw();

Also add the assignment operator to 20.6.4.3 [meta.unary.prop]:

>     auto_ptr& operator=(auto_ptr_ref<X> r) throw()

> Effects: Calls `reset(p.release())` for the `auto_ptr p` that `r` holds a reference to.
> Returns: `*this`.

### 129. Need error indication from seekp() and seekg()

Section: 27.7.1.3 [istream.unformatted], 27.7.2.5 [ostream.seeks] Status: TC1 Submitter: Angelika Langer Opened: 1999-02-22 Last modified: 2008-09-26

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Discussion:

Currently, the standard does not specify how seekg() and seekp() indicate failure. They are not required to set failbit, and they can't return an error indication because they must return *this, i.e. the stream. Hence, it is undefined what happens if they fail. And they can fail, for instance, when a file stream is disconnected from the underlying file (is_open()==false) or when a wide character file stream must perform a state-dependent code conversion, etc.

The stream functions seekg() and seekp() should set failbit in the stream state in case of failure.

Proposed resolution:

Add to the Effects: clause of seekg() in 27.7.1.3 [istream.unformatted] and to the Effects: clause of seekp() in 27.7.2.5 [ostream.seeks]:

> In case of failure, the function calls `setstate(failbit)` (which may throw `ios_base::failure`).

Rationale:

Setting failbit is the usual error reporting mechanism for streams

### 130. Return type of container::erase(iterator) differs for associative containers

Section: 23.2.4 [associative.reqmts], 23.2.3 [sequence.reqmts] Status: CD1 Submitter: Andrew Koenig Opened: 1999-03-02 Last modified: 2009-05-01

View other active issues in [associative.reqmts].

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Duplicate of: 451

Discussion:

Table 67 (23.1.1) says that container::erase(iterator) returns an iterator. Table 69 (23.1.2) says that in addition to this requirement, associative containers also say that container::erase(iterator) returns void. That's not an addition; it's a change to the requirements, which has the effect of making associative containers fail to meet the requirements for containers.

Proposed resolution:

In 23.2.4 [associative.reqmts], in Table 69 Associative container requirements, change the return type of `a.erase(q)` from `void` to `iterator`. Change the assertion/not/pre/post-condition from "erases the element pointed to by `q`" to "erases the element pointed to by `q`. Returns an iterator pointing to the element immediately following q prior to the element being erased. If no such element exists, a.end() is returned."

In 23.2.4 [associative.reqmts], in Table 69 Associative container requirements, change the return type of `a.erase(q1, q2)` from `void` to `iterator`. Change the assertion/not/pre/post-condition from "erases the elements in the range `[q1, q2)`" to "erases the elements in the range `[q1, q2)`. Returns q2."

In 23.4.1 [map], in the `map` class synopsis; and in 23.4.2 [multimap], in the `multimap` class synopsis; and in 23.4.3 [set], in the `set` class synopsis; and in 23.4.4 [multiset], in the `multiset` class synopsis: change the signature of the first `erase` overload to

       iterator erase(iterator position);

and change the signature of the third `erase` overload to

      iterator erase(iterator first, iterator last);

[Pre-Kona: reopened at the request of Howard Hinnant]

[Post-Kona: the LWG agrees the return type should be `iterator`, not `void`. (Alex Stepanov agrees too.) Matt provided wording.]

[ Sydney: the proposed wording went in the right direction, but it wasn't good enough. We want to return an iterator from the range form of erase as well as the single-iterator form. Also, the wording is slightly different from the wording we have for sequences; there's no good reason for having a difference. Matt provided new wording, (reflected above) which we will review at the next meeting. ]

[ Redmond: formally voted into WP. ]

### 132. list::resize description uses random access iterators

Section: 23.3.4.2 [list.capacity] Status: TC1 Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2008-09-26

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Discussion:

The description reads:

-1- Effects:

             if (sz > size())
               insert(end(), sz-size(), c);
             else if (sz < size())
               erase(begin()+sz, end());
             else
               ;                           //  do nothing

Obviously list::resize should not be specified in terms of random access iterators.

Proposed resolution:

Change 23.3.4.2 [list.capacity] paragraph 1 to:

Effects:

             if (sz > size())
               insert(end(), sz-size(), c);
             else if (sz < size())
             {
               iterator i = begin();
               advance(i, sz);
               erase(i, end());
             }

[Dublin: The LWG asked Howard to discuss exception safety offline with David Abrahams. They had a discussion and believe there is no issue of exception safety with the proposed resolution.]

### 133. map missing get_allocator()

Section: 23.4.1 [map] Status: TC1 Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2008-09-26

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Discussion:

The title says it all.

Proposed resolution:

Insert in 23.4.1 [map], paragraph 2, after operator= in the map declaration:

        allocator_type get_allocator() const;

### 134. vector constructors over specified

Section: 23.3.6.1 [vector.cons] Status: TC1 Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2008-09-26

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Discussion:

The complexity description says: "It does at most 2N calls to the copy constructor of T and logN reallocations if they are just input iterators ...".

This appears to be overly restrictive, dictating the precise memory/performance tradeoff for the implementor.

Proposed resolution:

Change 23.3.6.1 [vector.cons], paragraph 1 to:

-1- Complexity: The constructor template <class InputIterator> vector(InputIterator first, InputIterator last) makes only N calls to the copy constructor of T (where N is the distance between first and last) and no reallocations if iterators first and last are of forward, bidirectional, or random access categories. It makes order N calls to the copy constructor of T and order logN reallocations if they are just input iterators.

Rationale:

"at most 2N calls" is correct only if the growth factor is greater than or equal to 2.

### 136. seekp, seekg setting wrong streams?

Section: 27.7.1.3 [istream.unformatted] Status: CD1 Submitter: Howard Hinnant Opened: 1999-03-06 Last modified: 2008-09-26

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Discussion:

I may be misunderstanding the intent, but should not seekg set only the input stream and seekp set only the output stream? The description seems to say that each should set both input and output streams. If that's really the intent, I withdraw this proposal.

Proposed resolution:

In section 27.6.1.3 change:

    basic_istream<charT,traits>& seekg(pos_type pos);
    Effects: If fail() != true, executes rdbuf()->pubseekpos(pos).

To:

    basic_istream<charT,traits>& seekg(pos_type pos);
    Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::in).

In section 27.6.1.3 change:

    basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir);
    Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir).

To:

    basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir);
    Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::in).

In section 27.6.2.4, paragraph 2 change:

    -2- Effects: If fail() != true, executes rdbuf()->pubseekpos(pos).

To:

    -2- Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::out).

In section 27.6.2.4, paragraph 4 change:

    -4- Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir).

To:

    -4- Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::out).

[Dublin: Dietmar Kühl thinks this is probably correct, but would like the opinion of more iostream experts before taking action.]

[Tokyo: Reviewed by the LWG. PJP noted that although his docs are incorrect, his implementation already implements the Proposed Resolution.]

[Post-Tokyo: Matt Austern comments:
Is it a problem with basic_istream and basic_ostream, or is it a problem with basic_stringbuf? We could resolve the issue either by changing basic_istream and basic_ostream, or by changing basic_stringbuf. I prefer the latter change (or maybe both changes): I don't see any reason for the standard to require that std::stringbuf s(std::string("foo"), std::ios_base::in); s.pubseekoff(0, std::ios_base::beg); must fail.
This requirement is a bit weird. There's no similar requirement for basic_streambuf<>::seekpos, or for basic_filebuf<>::seekoff or basic_filebuf<>::seekpos.]

### 137. Do use_facet and has_facet look in the global locale?

Section: 22.3.1 [locale] Status: TC1 Submitter: Angelika Langer Opened: 1999-03-17 Last modified: 2008-09-26

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Discussion:

Section 22.3.1 [locale] says:

-4- In the call to use_facet<Facet>(loc), the type argument chooses a facet, making available all members of the named type. If Facet is not present in a locale (or, failing that, in the global locale), it throws the standard exception bad_cast. A C++ program can check if a locale implements a particular facet with the template function has_facet<Facet>().

This contradicts the specification given in section 22.3.2 [locale.global.templates]:
template <class Facet> const Facet& use_facet(const locale& loc);
-1- Get a reference to a facet of a locale.
-2- Returns: a reference to the corresponding facet of loc, if present.
-3- Throws: bad_cast if has_facet<Facet>(loc) is false.
-4- Notes: The reference returned remains valid at least as long as any copy of loc exists

Proposed resolution:

Remove the phrase "(or, failing that, in the global locale)" from section 22.1.1.

Rationale:

Needed for consistency with the way locales are handled elsewhere in the standard.

### 139. Optional sequence operation table description unclear

Section: 23.2.3 [sequence.reqmts] Status: TC1 Submitter: Andrew Koenig Opened: 1999-03-30 Last modified: 2008-09-26

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Discussion:

The sentence introducing the Optional sequence operation table (23.1.1 paragraph 12) has two problems:

A. It says ``The operations in table 68 are provided only for the containers for which they take constant time.''
That could be interpreted in two ways, one of them being ``Even though table 68 shows particular operations as being provided, implementations are free to omit them if they cannot implement them in constant time.''
B. That paragraph says nothing about amortized constant time, and it should.

Proposed resolution:

Replace the wording in 23.1.1 paragraph 12 which begins ``The operations in table 68 are provided only..." with:

> Table 68 lists sequence operations that are provided for some types of sequential containers but not others. An implementation shall provide these operations for all container types shown in the ``container'' column, and shall implement them so as to take amortized constant time.

### 141. basic_string::find_last_of, find_last_not_of say pos instead of xpos

Section: 21.4.6.4 [string::insert], 21.4.6.6 [string::replace] Status: TC1 Submitter: Arch Robison Opened: 1999-04-28 Last modified: 2008-09-26

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Discussion:

Sections 21.3.6.4 paragraph 1 and 21.3.6.6 paragraph 1 surely have misprints where they say:
— `xpos <= pos` and `pos < size();`

Surely the document meant to say ```xpos < size()`'' in both places.

[Judy Ward also sent in this issue for 21.3.6.4 with the same proposed resolution.]

Proposed resolution:

Change Sections 21.3.6.4 paragraph 1 and 21.3.6.6 paragraph 1, the line which says:
— `xpos <= pos` and `pos < size();
` to:
`
` — `xpos <= pos` and `xpos < size();`

### 142. lexicographical_compare complexity wrong

Section: 25.4.8 [alg.lex.comparison] Status: TC1 Submitter: Howard Hinnant Opened: 1999-06-20 Last modified: 2008-09-26

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Discussion:

The lexicographical_compare complexity is specified as:
"At most min((last1 - first1), (last2 - first2)) applications of the corresponding comparison."
The best I can do is twice that expensive.

Nicolai Josuttis comments in lib-6862: You mean, to check for equality you have to check both < and >? Yes, IMO you are right! (and Matt states this complexity in his book)

Proposed resolution:

Change 25.4.8 [alg.lex.comparison] complexity to:

> At most `2*min((last1 - first1), (last2 - first2))` applications of the corresponding comparison.

Change the example at the end of paragraph 3 to read:

> [Example:
> for ( ; first1 != last1 && first2 != last2 ; ++first1, ++first2) {
> if (*first1 < *first2) return true;
> if (*first2 < *first1) return false;
> }
> return first1 == last1 && first2 != last2;
> --end example]

### 144. Deque constructor complexity wrong

Section: 23.3.2.1 [deque.cons] Status: TC1 Submitter: Herb Sutter Opened: 1999-05-09 Last modified: 2008-09-26

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Discussion:

In 23.3.2.1 [deque.cons] paragraph 6, the deque ctor that takes an iterator range appears to have complexity requirements which are incorrect, and which contradict the complexity requirements for insert(). I suspect that the text in question, below, was taken from vector:

> Complexity: If the iterators first and last are forward iterators, bidirectional iterators, or random access iterators the constructor makes only N calls to the copy constructor, and performs no reallocations, where N is last - first.

The word "reallocations" does not really apply to deque. Further, all of the following appears to be spurious:

> It makes at most 2N calls to the copy constructor of T and log N reallocations if they are input iterators.1)

> 1) The complexity is greater in the case of input iterators because each element must be added individually: it is impossible to determine the distance between first abd last before doing the copying.

This makes perfect sense for vector, but not for deque. Why should deque gain an efficiency advantage from knowing in advance the number of elements to insert?

Proposed resolution:

In 23.3.2.1 [deque.cons] paragraph 6, replace the Complexity description, including the footnote, with the following text (which also corrects the "abd" typo):

> Complexity: Makes last - first calls to the copy constructor of T.

### 146. complex<T> Inserter and Extractor need sentries

Section: 26.4.6 [complex.ops] Status: TC1 Submitter: Angelika Langer Opened: 1999-05-12 Last modified: 2008-09-26

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Discussion:

The extractor for complex numbers is specified as:

> template<class T, class charT, class traits>
> basic_istream<charT, traits>&
> operator>>(basic_istream<charT, traits>& is, complex<T>& x);
> Effects: Extracts a complex number x of the form: u, (u), or (u,v), where u is the real part and v is the imaginary part (lib.istream.formatted).
> Requires: The input values be convertible to T. If bad input is encountered, calls is.setstate(ios::failbit) (which may throw ios::failure (lib.iostate.flags).
> Returns: is .

Is it intended that the extractor for complex numbers does not skip whitespace, unlike all other extractors in the standard library do? Shouldn't a sentry be used?
The inserter for complex numbers is specified as:

> template<class T, class charT, class traits>
> basic_ostream<charT, traits>&
> operator<<(basic_ostream<charT, traits>& o, const complex<T>& x);
> Effects: inserts the complex number x onto the stream o as if it were implemented as follows:
> template<class T, class charT, class traits>
> basic_ostream<charT, traits>&
> operator<<(basic_ostream<charT, traits>& o, const complex<T>& x)
> {
> basic_ostringstream<charT, traits> s;
> s.flags(o.flags());
> s.imbue(o.getloc());
> s.precision(o.precision());
> s << '(' << x.real() << "," << x.imag() << ')';
> return o << s.str();
> }

Is it intended that the inserter for complex numbers ignores the field width and does not do any padding? If, with the suggested implementation above, the field width were set in the stream then the opening parentheses would be adjusted, but the rest not, because the field width is reset to zero after each insertion.

I think that both operations should use sentries, for sake of consistency with the other inserters and extractors in the library. Regarding the issue of padding in the inserter, I don't know what the intent was.

Proposed resolution:

After 26.4.6 [complex.ops] paragraph 14 (operator>>), add a Notes clause:

> Notes: This extraction is performed as a series of simpler extractions. Therefore, the skipping of whitespace is specified to be the same for each of the simpler extractions.

Rationale:

For extractors, the note is added to make it clear that skipping whitespace follows an "all-or-none" rule.

For inserters, the LWG believes there is no defect; the standard is correct as written.

### 147. Library Intro refers to global functions that aren't global

Section: 17.6.4.4 [global.functions] Status: TC1 Submitter: Lois Goldthwaite Opened: 1999-06-04 Last modified: 2008-09-26

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Discussion:

The library had many global functions until 17.4.1.1 [lib.contents] paragraph 2 was added:

> All library entities except macros, operator new and operator delete are defined within the namespace std or namespaces nested within namespace std.

It appears "global function" was never updated in the following:

> 17.4.4.3 - Global functions [lib.global.functions]
> -1- It is unspecified whether any global functions in the C++ Standard Library are defined as inline (dcl.fct.spec).
> -2- A call to a global function signature described in Clauses lib.language.support through lib.input.output behaves the same as if the implementation declares no additional global function signatures.*
> [Footnote: A valid C++ program always calls the expected library global function. An implementation may also define additional global functions that would otherwise not be called by a valid C++ program. --- end footnote]
> -3- A global function cannot be declared by the implementation as taking additional default arguments.
> 17.4.4.4 - Member functions [lib.member.functions]
> -2- An implementation can declare additional non-virtual member function signatures within a class:

> > -- by adding arguments with default values to a member function signature; The same latitude does not extend to the implementation of virtual or global functions, however.

Proposed resolution:

Change "global" to "global or non-member" in:

> 17.4.4.3 [lib.global.functions] section title,
> 17.4.4.3 [lib.global.functions] para 1,
> 17.4.4.3 [lib.global.functions] para 2 in 2 places plus 2 places in the footnote,
> 17.4.4.3 [lib.global.functions] para 3,
> 17.4.4.4 [lib.member.functions] para 2

Rationale:

Because operator new and delete are global, the proposed resolution was changed from "non-member" to "global or non-member.

### 148. Functions in the example facet BoolNames should be const

Section: 22.4.8 [facets.examples] Status: TC1 Submitter: Jeremy Siek Opened: 1999-06-03 Last modified: 2008-09-26

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Discussion:

In 22.4.8 [facets.examples] paragraph 13, the do_truename() and do_falsename() functions in the example facet BoolNames should be const. The functions they are overriding in numpunct_byname<char> are const.

Proposed resolution:

In 22.4.8 [facets.examples] paragraph 13, insert "const" in two places:

> `string do_truename() const { return "Oui Oui!"; }
> string do_falsename() const { return "Mais Non!"; }`

### 149. Insert should return iterator to first element inserted

Section: 23.2.3 [sequence.reqmts] Status: WP Submitter: Andrew Koenig Opened: 1999-06-28 Last modified: 2009-10-26

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Discussion:

Suppose that c and c1 are sequential containers and i is an iterator that refers to an element of c. Then I can insert a copy of c1's elements into c ahead of element i by executing

>     c.insert(i, c1.begin(), c1.end());

If c is a vector, it is fairly easy for me to find out where the newly inserted elements are, even though i is now invalid:

>     size_t i_loc = i - c.begin();
>     c.insert(i, c1.begin(), c1.end());

and now the first inserted element is at c.begin()+i_loc and one past the last is at c.begin()+i_loc+c1.size().
But what if c is a list? I can still find the location of one past the last inserted element, because i is still valid. To find the location of the first inserted element, though, I must execute something like

>     for (size_t n = c1.size(); n; --n)
>        --i;

because i is now no longer a random-access iterator.
Alternatively, I might write something like

>     bool first = i == c.begin();
>     list<T>::iterator j = i;
>     if (!first) --j;
>     c.insert(i, c1.begin(), c1.end());
>     if (first)
>        j = c.begin();
>     else
>        ++j;

which, although wretched, requires less overhead.
But I think the right solution is to change the definition of insert so that instead of returning void, it returns an iterator that refers to the first element inserted, if any, and otherwise is a copy of its first argument.

[ Summit: ]

> Reopened by Alisdair.

[ Post Summit Alisdair adds: ]

> In addition to the original rationale for C++03, this change also gives a consistent interface for all container insert operations i.e. they all return an iterator to the (first) inserted item.

> Proposed wording provided.

[ 2009-07 Frankfurt ]

> Q: why isn't this change also proposed for associative containers?

> A: The returned iterator wouldn't necessarily point to a contiguous range.

> Moved to Ready.

Proposed resolution:

Table 83 change return type from `void` to `iterator` for the following rows:

> Table 83 -- Sequence container requirements (in addition to container)
> Expression | Return type | Assertion/note pre-/post-condition
> --- | --- | ---
> `a.insert(p,n,t)` | `void iterator` | Inserts `n` copies of `t` before `p`.
> `a.insert(p,i,j)` | `void iterator` | Each iterator in the range `[i,j)` shall be dereferenced exactly once. pre: `i` and `j` are not iterators into `a`. Inserts copies of elements in `[i, j)` before `p`
> `a.insert(p,il)` | `void iterator` | `a.insert(p, il.begin(), il.end())`.

Add after p6 23.2.3 [sequence.reqmts]:

> -6- ...

> The iterator returned from `a.insert(p,n,t)` points to the copy of the first element inserted into `a`, or `p` if `n == 0`.

> The iterator returned from `a.insert(p,i,j)` points to the copy of the first element inserted into `a`, or `p` if `i == j`.

> The iterator returned from `a.insert(p,il)` points to the copy of the first element inserted into `a`, or `p` if `il` is empty.

p2 23.3.2 [deque] Update class definition, change return type from `void` to `iterator`:

>     void iterator insert(const_iterator position, size_type n, const T& x);
>     template <class InputIterator>
>       void iterator insert(const_iterator position, InputIterator first, InputIterator last);
>       void iterator insert(const_iterator position, initializer_list<T>);

23.3.2.3 [deque.modifiers] change return type from `void` to `iterator` on following declarations:

>       void iterator insert(const_iterator position, size_type n, const T& x);
>     template <class InputIterator>
>       void iterator insert(const_iterator position, InputIterator first, InputIterator last);

Add the following (missing) declaration

>     iterator insert(const_iterator position, initializer_list<T>);

23.3.3 [forwardlist] Update class definition, change return type from `void` to `iterator`:

>     void iterator insert_after(const_iterator position, initializer_list<T> il);
>     void iterator insert_after(const_iterator position, size_type n, const T& x);
>     template <class InputIterator>
>       void iterator insert_after(const_iterator position, InputIterator first, InputIterator last);

p8 23.3.3.4 [forwardlist.modifiers] change return type from `void` to `iterator`:

>     void iterator insert_after(const_iterator position, size_type n, const T& x);

Add paragraph:

> Returns: position.

p10 23.3.3.4 [forwardlist.modifiers] change return type from `void` to `iterator`:

>     template <class InputIterator>
>       void iterator insert_after(const_iterator position, InputIterator first, InputIterator last);

Add paragraph:

> Returns: position.

p12 23.3.3.4 [forwardlist.modifiers] change return type from `void` to `iterator` on following declarations:

>     void iterator insert_after(const_iterator position, initializer_list<T> il);

change return type from `void` to `iterator` on following declarations:

p2 23.3.4 [list] Update class definition, change return type from `void` to `iterator`:

>     void iterator insert(const_iterator position, size_type n, const T& x);

>     template <class InputIterator>
>     void iterator insert(const_iterator position, InputIterator first, InputIterator last);

>     void iterator insert(const_iterator position, initializer_list<T>);

23.3.4.3 [list.modifiers] change return type from `void` to `iterator` on following declarations:

>     void iterator insert(const_iterator position, size_type n, const T& x);

>     template <class InputIterator>
>       void iterator insert(const_iterator position, InputIterator first, InputIterator last);

Add the following (missing) declaration

>     iterator insert(const_iterator position, initializer_list<T>);

p2 23.3.6 [vector]

Update class definition, change return type from `void` to `iterator`:

>     void iterator insert(const_iterator position, T&& x);

>     void iterator insert(const_iterator position, size_type n, const T& x);

>     template <class InputIterator>
>       void iterator insert(const_iterator position, InputIterator first, InputIterator last);

>     void iterator insert(const_iterator position, initializer_list<T>);

23.3.6.4 [vector.modifiers] change return type from `void` to `iterator` on following declarations:

>     void iterator insert(const_iterator position, size_type n, const T& x);

>     template <class InputIterator>
>       void iterator insert(const_iterator position, InputIterator first, InputIterator last);

Add the following (missing) declaration

>     iterator insert(const_iterator position, initializer_list<T>);

p1 23.3.7 [vector.bool] Update class definition, change return type from `void` to `iterator`:

>     void iterator insert (const_iterator position, size_type n, const bool& x);

>     template <class InputIterator>
>       void iterator insert(const_iterator position, InputIterator first, InputIterator last);

>       void iterator insert(const_iterator position, initializer_list<bool> il);

p5 21.4 [basic.string] Update class definition, change return type from `void` to `iterator`:

>     void iterator insert(const_iterator p, size_type n, charT c);

>     template<class InputIterator>
>       void iterator insert(const_iterator p, InputIterator first, InputIterator last);

>     void iterator insert(const_iterator p, initializer_list<charT>);

p13 21.4.6.4 [string::insert] change return type from `void` to `iterator`:

>     void iterator insert(const_iterator p, size_type n, charT c);

Add paragraph:

> Returns: an iterator which refers to the copy of the first inserted character, or `p` if `n == 0`.

p15 21.4.6.4 [string::insert] change return type from `void` to `iterator`:

>     template<class InputIterator>
>       void iterator insert(const_iterator p, InputIterator first, InputIterator last);

Add paragraph:

> Returns: an iterator which refers to the copy of the first inserted character, or `p` if `first == last`.

p17 21.4.6.4 [string::insert] change return type from `void` to `iterator`:

>     void iterator insert(const_iterator p, initializer_list<charT> il);

Add paragraph:

> Returns: an iterator which refers to the copy of the first inserted character, or `p` if `il` is empty.

Rationale:

[ The following was the C++98/03 rationale and does not necessarily apply to the proposed resolution in the C++0X time frame: ]

> The LWG believes this was an intentional design decision and so is not a defect. It may be worth revisiting for the next standard.

### 150. Find_first_of says integer instead of iterator

Section: 25.2.7 [alg.find.first.of] Status: TC1 Submitter: Matt McClure Opened: 1999-06-30 Last modified: 2008-09-26

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Discussion:

Proposed resolution:

Change 25.2.7 [alg.find.first.of] paragraph 2 from:

> Returns: The first iterator i in the range [first1, last1) such that for some integer j in the range [first2, last2) ...

to:

> Returns: The first iterator i in the range [first1, last1) such that for some iterator j in the range [first2, last2) ...

### 151. Can't currently clear() empty container

Section: 23.2.3 [sequence.reqmts] Status: TC1 Submitter: Ed Brey Opened: 1999-06-21 Last modified: 2008-09-26

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Discussion:

For both sequences and associative containers, a.clear() has the semantics of erase(a.begin(),a.end()), which is undefined for an empty container since erase(q1,q2) requires that q1 be dereferenceable (23.1.1,3 and 23.1.2,7). When the container is empty, a.begin() is not dereferenceable.
The requirement that q1 be unconditionally dereferenceable causes many operations to be intuitively undefined, of which clearing an empty container is probably the most dire.
Since q1 and q2 are only referenced in the range [q1, q2), and [q1, q2) is required to be a valid range, stating that q1 and q2 must be iterators or certain kinds of iterators is unnecessary.

Proposed resolution:

In 23.1.1, paragraph 3, change:

> p and q2 denote valid iterators to a, q and q1 denote valid dereferenceable iterators to a, [q1, q2) denotes a valid range

to:

> p denotes a valid iterator to a, q denotes a valid dereferenceable iterator to a, [q1, q2) denotes a valid range in a

In 23.1.2, paragraph 7, change:

> p and q2 are valid iterators to a, q and q1 are valid dereferenceable iterators to a, [q1, q2) is a valid range

to

> p is a valid iterator to a, q is a valid dereferenceable iterator to a, [q1, q2) is a valid range into a

### 152. Typo in `scan_is()` semantics

Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The semantics of `scan_is()` (paragraphs 4 and 6) is not exactly described because there is no function `is()` which only takes a character as argument. Also, in the effects clause (paragraph 3), the semantic is also kept vague.

Proposed resolution:

In 22.4.1.1.2 [locale.ctype.virtuals] paragraphs 4 and 6, change the returns clause from:

> "... such that `is(*p)` would..."

to: "... such that `is(m, *p)` would...."

### 153. Typo in `narrow()` semantics

Section: 22.4.1.3.2 [facet.ctype.char.members] Status: CD1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Duplicate of: 207

Discussion:

The description of the array version of `narrow()` (in paragraph 11) is flawed: There is no member `do_narrow()` which takes only three arguments because in addition to the range a default character is needed.

Additionally, for both `widen` and `narrow` we have two signatures followed by a Returns clause that only addresses one of them.

Proposed resolution:

Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] paragraph 10 from:

Returns: do_widen(low, high, to).

to:

Returns: do_widen(c) or do_widen(low, high, to), respectively.

Change 22.4.1.3.2 [facet.ctype.char.members] paragraph 10 and 11 from:

            char        narrow(char c, char /*dfault*/) const;
            const char* narrow(const char* low, const char* high,
                               char /*dfault*/, char* to) const;

            Returns: do_narrow(low, high, to).

to:

            char        narrow(char c, char dfault) const;
            const char* narrow(const char* low, const char* high,
                               char dfault, char* to) const;

            Returns: do_narrow(c, dfault) or
                     do_narrow(low, high, dfault, to), respectively.

[Kona: 1) the problem occurs in additional places, 2) a user defined version could be different.]

[Post-Tokyo: Dietmar provided the above wording at the request of the LWG. He could find no other places the problem occurred. He asks for clarification of the Kona "a user defined version..." comment above. Perhaps it was a circuitous way of saying "dfault" needed to be uncommented?]

[Post-Toronto: the issues list maintainer has merged in the proposed resolution from issue 207, which addresses the same paragraphs.]

### 154. Missing `double` specifier for `do_get()`

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The table in paragraph 7 for the length modifier does not list the length modifier `l` to be applied if the type is `double`. Thus, the standard asks the implementation to do undefined things when using `scanf()` (the missing length modifier for `scanf()` when scanning `double`s is actually a problem I found quite often in production code, too).

Proposed resolution:

In 22.4.2.1.2 [facet.num.get.virtuals], paragraph 7, add a row in the Length Modifier table to say that for `double` a length modifier `l` is to be used.

Rationale:

The standard makes an embarrassing beginner's mistake.

### 155. Typo in naming the class defining the class `Init`

Section: 27.4 [iostream.objects] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

There are conflicting statements about where the class `Init` is defined. According to 27.4 [iostream.objects] paragraph 2 it is defined as `basic_ios::Init`, according to 27.5.2 [ios.base] it is defined as `ios_base::Init`.

Proposed resolution:

Change 27.4 [iostream.objects] paragraph 2 from "`basic_ios::Init"` to "`ios_base::Init"`.

Rationale:

Although not strictly wrong, the standard was misleading enough to warrant the change.

### 156. Typo in `imbue()` description

Section: 27.5.2.3 [ios.base.locales] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

There is a small discrepancy between the declarations of `imbue()`: in 27.5.2 [ios.base] the argument is passed as `locale const&` (correct), in 27.5.2.3 [ios.base.locales] it is passed as `locale const` (wrong).

Proposed resolution:

In 27.5.2.3 [ios.base.locales] change the `imbue` argument from "`locale const" to "locale const&".`

### 158. Underspecified semantics for `setbuf()`

Section: 27.6.2.4.2 [streambuf.virt.buffer] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The default behavior of `setbuf()` is described only for the situation that `gptr() != 0 && gptr() != egptr()`: namely to do nothing. What has to be done in other situations is not described although there is actually only one reasonable approach, namely to do nothing, too.

Since changing the buffer would almost certainly mess up most buffer management of derived classes unless these classes do it themselves, the default behavior of `setbuf()` should always be to do nothing.

Proposed resolution:

Change 27.6.2.4.2 [streambuf.virt.buffer], paragraph 3, Default behavior, to: "Default behavior: Does nothing. Returns this."

### 159. Strange use of `underflow()`

Section: 27.6.2.4.3 [streambuf.virt.get] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The description of the meaning of the result of `showmanyc()` seems to be rather strange: It uses calls to `underflow()`. Using `underflow()` is strange because this function only reads the current character but does not extract it, `uflow()` would extract the current character. This should be fixed to use `sbumpc()` instead.

Proposed resolution:

Change 27.6.2.4.3 [streambuf.virt.get] paragraph 1, `showmanyc()`returns clause, by replacing the word "supplied" with the words "extracted from the stream".

### 160. Typo: Use of non-existing function `exception()`

Section: 27.7.1.1 [istream] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The paragraph 4 refers to the function `exception()` which is not defined. Probably, the referred function is `basic_ios<>::exceptions()`.

Proposed resolution:

In 27.7.1.1 [istream], 27.7.1.3 [istream.unformatted], paragraph 1, 27.7.2.1 [ostream], paragraph 3, and 27.7.2.6.1 [ostream.formatted.reqmts], paragraph 1, change "`exception()" to "exceptions()"`.

[Note to Editor: "exceptions" with an "s" is the correct spelling.]

### 161. Typo: `istream_iterator` vs. `istreambuf_iterator`

Section: 27.7.1.2.2 [istream.formatted.arithmetic] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The note in the second paragraph pretends that the first argument is an object of type `istream_iterator`. This is wrong: It is an object of type `istreambuf_iterator`.

Proposed resolution:

Change 27.7.1.2.2 [istream.formatted.arithmetic] from:

> The first argument provides an object of the istream_iterator class...

to

> The first argument provides an object of the istreambuf_iterator class...

### 164. do_put() has apparently unused fill argument

Section: 22.4.5.3.2 [locale.time.put.virtuals] Status: TC1 Submitter: Angelika Langer Opened: 1999-07-23 Last modified: 2008-09-26

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Discussion:

In 22.4.5.3.2 [locale.time.put.virtuals] the do_put() function is specified as taking a fill character as an argument, but the description of the function does not say whether the character is used at all and, if so, in which way. The same holds for any format control parameters that are accessible through the ios_base& argument, such as the adjustment or the field width. Is strftime() supposed to use the fill character in any way? In any case, the specification of time_put.do_put() looks inconsistent to me.
Is the signature of do_put() wrong, or is the effects clause incomplete?

Proposed resolution:

Add the following note after 22.4.5.3.2 [locale.time.put.virtuals] paragraph 2:

> [Note: the `fill` argument may be used in the implementation-defined formats, or by derivations. A space character is a reasonable default for this argument. --end Note]

Rationale:

The LWG felt that while the normative text was correct, users need some guidance on what to pass for the `fill` argument since the standard doesn't say how it's used.

### 165. `xsputn()`, `pubsync()` never called by `basic_ostream` members?

Section: 27.7.2.1 [ostream] Status: CD1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

Paragraph 2 explicitly states that none of the `basic_ostream` functions falling into one of the groups "formatted output functions" and "unformatted output functions" calls any stream buffer function which might call a virtual function other than `overflow()`. Basically this is fine but this implies that `sputn()` (this function would call the virtual function `xsputn()`) is never called by any of the standard output functions. Is this really intended? At minimum it would be convenient to call `xsputn()` for strings... Also, the statement that `overflow()` is the only virtual member of `basic_streambuf` called is in conflict with the definition of `flush()` which calls `rdbuf()->pubsync()` and thereby the virtual function `sync()` (`flush()` is listed under "unformatted output functions").

In addition, I guess that the sentence starting with "They may use other public members of `basic_ostream` ..." probably was intended to start with "They may use other public members of `basic_streamuf`..." although the problem with the virtual members exists in both cases.

I see two obvious resolutions:

1. state in a footnote that this means that `xsputn()` will never be called by any ostream member and that this is intended.
2. relax the restriction and allow calling `overflow()` and `xsputn()`. Of course, the problem with `flush()` has to be resolved in some way.

Proposed resolution:

Change the last sentence of 27.6.2.1 (lib.ostream) paragraph 2 from:

> They may use other public members of basic_ostream except that they do not invoke any virtual members of rdbuf() except overflow().

to:

> They may use other public members of basic_ostream except that they shall not invoke any virtual members of rdbuf() except overflow(), xsputn(), and sync().

[Kona: the LWG believes this is a problem. Wish to ask Jerry or PJP why the standard is written this way.]

[Post-Tokyo: Dietmar supplied wording at the request of the LWG. He comments: The rules can be made a little bit more specific if necessary be explicitly spelling out what virtuals are allowed to be called from what functions and eg to state specifically that flush() is allowed to call sync() while other functions are not.]

### 167. Improper use of `traits_type::length()`

Section: 27.7.2.6.4 [ostream.inserters.character] Status: CD1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

Paragraph 4 states that the length is determined using `traits::length(s)`. Unfortunately, this function is not defined for example if the character type is `wchar_t` and the type of `s` is `char const*`. Similar problems exist if the character type is `char` and the type of `s` is either `signed char const*` or `unsigned char const*`.

Proposed resolution:

Change 27.7.2.6.4 [ostream.inserters.character] paragraph 4 from:

> Effects: Behaves like an formatted inserter (as described in lib.ostream.formatted.reqmts) of out. After a sentry object is constructed it inserts characters. The number of characters starting at s to be inserted is traits::length(s). Padding is determined as described in lib.facet.num.put.virtuals. The traits::length(s) characters starting at s are widened using out.widen (lib.basic.ios.members). The widened characters and any required padding are inserted into out. Calls width(0).

to:

> Effects: Behaves like a formatted inserter (as described in lib.ostream.formatted.reqmts) of out. After a sentry object is constructed it inserts n characters starting at s, where n is the number that would be computed as if by:

> - traits::length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const charT*, and also for the overload where the first argument is of type basic_ostream<char, traits>& and the second is of type const char*.
> - std::char_traits<char>::length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const char*.
> - traits::length(reinterpret_cast<const char*>(s)) for the other two overloads.

> Padding is determined as described in lib.facet.num.put.virtuals. The n characters starting at s are widened using out.widen (lib.basic.ios.members). The widened characters and any required padding are inserted into out. Calls width(0).

[Santa Cruz: Matt supplied new wording]

[Kona: changed "where n is" to " where n is the number that would be computed as if by"]

Rationale:

We have five separate cases. In two of them we can use the user-supplied traits class without any fuss. In the other three we try to use something as close to that user-supplied class as possible. In two cases we've got a traits class that's appropriate for char and what we've got is a const signed char* or a const unsigned char*; that's close enough so we can just use a reinterpret cast, and continue to use the user-supplied traits class. Finally, there's one case where we just have to give up: where we've got a traits class for some arbitrary charT type, and we somehow have to deal with a const char*. There's nothing better to do but fall back to char_traits<char>

### 168. Typo: formatted vs. unformatted

Section: 27.7.2.7 [ostream.unformatted] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The first paragraph begins with a descriptions what has to be done in formatted output functions. Probably this is a typo and the paragraph really want to describe unformatted output functions...

Proposed resolution:

In 27.7.2.7 [ostream.unformatted] paragraph 1, the first and last sentences, change the word "formatted" to "unformatted":

> "Each unformatted output function begins ..."
> "... value specified for the unformatted output function."

### 169. Bad efficiency of `overflow()` mandated

Section: 27.8.1.4 [stringbuf.virtuals] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

Paragraph 8, Notes, of this section seems to mandate an extremely inefficient way of buffer handling for `basic_stringbuf`, especially in view of the restriction that `basic_ostream` member functions are not allowed to use `xsputn()` (see 27.7.2.1 [ostream]): For each character to be inserted, a new buffer is to be created.

Of course, the resolution below requires some handling of simultaneous input and output since it is no longer possible to update `egptr()` whenever `epptr()` is changed. A possible solution is to handle this in `underflow()`.

Proposed resolution:

In 27.8.1.4 [stringbuf.virtuals] paragraph 8, Notes, insert the words "at least" as in the following:

> To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus at least one additional write position.

### 170. Inconsistent definition of `traits_type`

Section: 27.8.4 [stringstream] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

The classes `basic_stringstream` (27.8.4 [stringstream]), `basic_istringstream` (27.8.2 [istringstream]), and `basic_ostringstream` (27.8.3 [ostringstream]) are inconsistent in their definition of the type `traits_type`: For `istringstream`, this type is defined, for the other two it is not. This should be consistent.

Proposed resolution:

Proposed resolution:

To the declarations of `basic_ostringstream` (27.8.3 [ostringstream]) and `basic_stringstream` (27.8.4 [stringstream]) add:

>     typedef traits traits_type;

### 171. Strange `seekpos()` semantics due to joint position

Section: 27.9.1.5 [filebuf.virtuals] Status: CD1 Submitter: Dietmar Kühl Opened: 1999-07-20 Last modified: 2008-09-26

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Discussion:

Overridden virtual functions, seekpos()

In 27.9.1.1 [filebuf] paragraph 3, it is stated that a joint input and output position is maintained by `basic_filebuf`. Still, the description of `seekpos()` seems to talk about different file positions. In particular, it is unclear (at least to me) what is supposed to happen to the output buffer (if there is one) if only the input position is changed. The standard seems to mandate that the output buffer is kept and processed as if there was no positioning of the output position (by changing the input position). Of course, this can be exactly what you want if the flag `ios_base::ate` is set. However, I think, the standard should say something like this:

- If `(which & mode) == 0` neither read nor write position is changed and the call fails. Otherwise, the joint read and write position is altered to correspond to `sp`.
- If there is an output buffer, the output sequences is updated and any unshift sequence is written before the position is altered.
- If there is an input buffer, the input sequence is updated after the position is altered.

Plus the appropriate error handling, that is...

Proposed resolution:

Change the unnumbered paragraph in 27.8.1.4 (lib.filebuf.virtuals) before paragraph 14 from:

> pos_type seekpos(pos_type sp, ios_base::openmode = ios_base::in | ios_base::out);

> Alters the file position, if possible, to correspond to the position stored in sp (as described below).

> - if (which&ios_base::in)!=0, set the file position to sp, then update the input sequence

> - if (which&ios_base::out)!=0, then update the output sequence, write any unshift sequence, and set the file position to sp.

to:

> pos_type seekpos(pos_type sp, ios_base::openmode = ios_base::in | ios_base::out);

> Alters the file position, if possible, to correspond to the position stored in sp (as described below). Altering the file position performs as follows:

> 1. if (om & ios_base::out)!=0, then update the output sequence and write any unshift sequence;

> 2. set the file position to sp;

> 3. if (om & ios_base::in)!=0, then update the input sequence;

> where om is the open mode passed to the last call to open(). The operation fails if is_open() returns false.

[Kona: Dietmar is working on a proposed resolution.]

[Post-Tokyo: Dietmar supplied the above wording.]

### 172. Inconsistent types for `basic_istream::ignore()`

Section: 27.7.1.3 [istream.unformatted] Status: TC1 Submitter: Greg Comeau, Dietmar Kühl Opened: 1999-07-23 Last modified: 2008-09-26

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Discussion:

In 27.7.1.1 [istream] the function `ignore()` gets an object of type `streamsize` as first argument. However, in 27.7.1.3 [istream.unformatted] paragraph 23 the first argument is of type `int.`

As far as I can see this is not really a contradiction because everything is consistent if `streamsize` is typedef to be `int`. However, this is almost certainly not what was intended. The same thing happened to `basic_filebuf::setbuf()`, as described in issue 173.

Darin Adler also submitted this issue, commenting: Either 27.6.1.1 should be modified to show a first parameter of type int, or 27.6.1.3 should be modified to show a first parameter of type streamsize and use numeric_limits<streamsize>::max.

Proposed resolution:

In 27.7.1.3 [istream.unformatted] paragraph 23 and 24, change both uses of `int` in the description of `ignore()` to `streamsize`.

### 173. Inconsistent types for `basic_filebuf::setbuf()`

Section: 27.9.1.5 [filebuf.virtuals] Status: TC1 Submitter: Greg Comeau, Dietmar Kühl Opened: 1999-07-23 Last modified: 2008-09-26

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Discussion:

In 27.9.1.1 [filebuf] the function `setbuf()` gets an object of type `streamsize` as second argument. However, in 27.9.1.5 [filebuf.virtuals] paragraph 9 the second argument is of type `int`.

As far as I can see this is not really a contradiction because everything is consistent if `streamsize` is typedef to be `int`. However, this is almost certainly not what was intended. The same thing happened to `basic_istream::ignore()`, as described in issue 172.

Proposed resolution:

In 27.9.1.5 [filebuf.virtuals] paragraph 9, change all uses of `int` in the description of `setbuf()` to `streamsize`.

### 174. Typo: `OFF_T` vs. `POS_T`

Section: D.7 [depr.ios.members] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-23 Last modified: 2008-09-26

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Discussion:

According to paragraph 1 of this section, `streampos` is the type `OFF_T`, the same type as `streamoff`. However, in paragraph 6 the `streampos` gets the type `POS_T`

Proposed resolution:

Change D.7 [depr.ios.members] paragraph 1 from "`typedef OFF_T streampos;`" to "`typedef POS_T streampos;`"

### 175. Ambiguity for `basic_streambuf::pubseekpos()` and a few other functions.

Section: D.7 [depr.ios.members] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-23 Last modified: 2008-09-26

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Discussion:

According to paragraph 8 of this section, the methods `basic_streambuf::pubseekpos()`, `basic_ifstream::open()`, and `basic_ofstream::open` "may" be overloaded by a version of this function taking the type `ios_base::open_mode` as last argument argument instead of `ios_base::openmode` (`ios_base::open_mode` is defined in this section to be an alias for one of the integral types). The clause specifies, that the last argument has a default argument in three cases. However, this generates an ambiguity with the overloaded version because now the arguments are absolutely identical if the last argument is not specified.

Proposed resolution:

In D.7 [depr.ios.members] paragraph 8, remove the default arguments for `basic_streambuf::pubseekpos()`, `basic_ifstream::open()`, and `basic_ofstream::open().`

### 176. `exceptions()` in `ios_base`...?

Section: D.7 [depr.ios.members] Status: TC1 Submitter: Dietmar Kühl Opened: 1999-07-23 Last modified: 2008-09-26

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Discussion:

The "overload" for the function `exceptions()` in paragraph 8 gives the impression that there is another function of this function defined in class `ios_base`. However, this is not the case. Thus, it is hard to tell how the semantics (paragraph 9) can be implemented: "Call the corresponding member function specified in clause 27 [input.output]."

Proposed resolution:

In D.7 [depr.ios.members] paragraph 8, move the declaration of the function `exceptions()`into class `basic_ios`.

### 179. Comparison of const_iterators to iterators doesn't work

Section: 23.2 [container.requirements] Status: CD1 Submitter: Judy Ward Opened: 1998-07-02 Last modified: 2008-09-26

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Discussion:

Currently the following will not compile on two well-known standard library implementations:

>     #include <set>
>     using namespace std;

>     void f(const set<int> &s)
>     {
>       set<int>::iterator i;
>       if (i==s.end()); // s.end() returns a const_iterator
>     }

The reason this doesn't compile is because operator== was implemented as a member function of the nested classes set:iterator and set::const_iterator, and there is no conversion from const_iterator to iterator. Surprisingly, (s.end() == i) does work, though, because of the conversion from iterator to const_iterator.

I don't see a requirement anywhere in the standard that this must work. Should there be one? If so, I think the requirement would need to be added to the tables in section 24.1.1. I'm not sure about the wording. If this requirement existed in the standard, I would think that implementors would have to make the comparison operators non-member functions.

This issues was also raised on comp.std.c++ by Darin Adler. The example given was:

>     bool check_equal(std::deque<int>::iterator i,
>     std::deque<int>::const_iterator ci)
>     {
>     return i == ci;
>     }

Comment from John Potter:

> In case nobody has noticed, accepting it will break reverse_iterator.

> The fix is to make the comparison operators templated on two types.

>         template <class Iterator1, class Iterator2>
>         bool operator== (reverse_iterator<Iterator1> const& x,
>                          reverse_iterator<Iterator2> const& y);

> Obviously: return x.base() == y.base();

> Currently, no reverse_iterator to const_reverse_iterator compares are valid.

> BTW, I think the issue is in support of bad code. Compares should be between two iterators of the same type. All std::algorithms require the begin and end iterators to be of the same type.

Proposed resolution:

Insert this paragraph after 23.2 [container.requirements] paragraph 7:

> In the expressions

>         i == j
>         i != j
>         i < j
>         i <= j
>         i >= j
>         i > j
>         i - j

> Where i and j denote objects of a container's iterator type, either or both may be replaced by an object of the container's const_iterator type referring to the same element with no change in semantics.

[post-Toronto: Judy supplied a proposed resolution saying that `iterator` and `const_iterator` could be freely mixed in iterator comparison and difference operations.]

[Redmond: Dave and Howard supplied a new proposed resolution which explicitly listed expressions; there was concern that the previous proposed resolution was too informal.]

Rationale:

The LWG believes it is clear that the above wording applies only to the nested types `X::iterator` and `X::const_iterator`, where `X` is a container. There is no requirement that `X::reverse_iterator` and `X::const_reverse_iterator` can be mixed. If mixing them is considered important, that's a separate issue. (Issue 280.)

### 180. Container member iterator arguments constness has unintended consequences

Section: 21.4 [basic.string] Status: CD1 Submitter: Dave Abrahams Opened: 1999-07-01 Last modified: 2008-09-26

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Discussion:

It is the constness of the container which should control whether it can be modified through a member function such as erase(), not the constness of the iterators. The iterators only serve to give positioning information.

Here's a simple and typical example problem which is currently very difficult or impossible to solve without the change proposed below.

Wrap a standard container C in a class W which allows clients to find and read (but not modify) a subrange of (C.begin(), C.end()]. The only modification clients are allowed to make to elements in this subrange is to erase them from C through the use of a member function of W.

[ post Bellevue, Alisdair adds: ]

> This issue was implemented by N2350 for everything but `basic_string`.

> Note that the specific example in this issue (`basic_string`) is the one place we forgot to amend in N2350, so we might open this issue for that single container?

[ Sophia Antipolis: ]

> This was a fix that was intended for all standard library containers, and has been done for other containers, but string was missed.

> The wording updated.

> We did not make the change in `replace`, because this change would affect the implementation because the string may be written into. This is an issue that should be taken up by concepts.

> We note that the supplied wording addresses the initializer list provided in N2679.

Proposed resolution:

Update the following signature in the `basic_string` class template definition in 21.4 [basic.string], p5:

>     namespace std {
>       template<class charT, class traits = char_traits<charT>,
>         class Allocator = allocator<charT> >
>       class basic_string {

>         ...

>         iterator insert(const_iterator p, charT c);
>         void insert(const_iterator p, size_type n, charT c);
>         template<class InputIterator>
>           void insert(const_iterator p, InputIterator first, InputIterator last);
>         void insert(const_iterator p, initializer_list<charT>);

>         ...

>         iterator erase(const_iterator const_position);
>         iterator erase(const_iterator first, const_iterator last);

>         ...

>       };
>     }

Update the following signatures in 21.4.6.4 [string::insert]:

>     iterator insert(const_iterator p, charT c);
>     void insert(const_iterator p, size_type n, charT c);
>     template<class InputIterator>
>       void insert(const_iterator p, InputIterator first, InputIterator last);
>     void insert(const_iterator p, initializer_list<charT>);

Update the following signatures in 21.4.6.5 [string::erase]:

>     iterator erase(const_iterator const_position);
>     iterator erase(const_iterator first, const_iterator last);

Rationale:

The issue was discussed at length. It was generally agreed that 1) There is no major technical argument against the change (although there is a minor argument that some obscure programs may break), and 2) Such a change would not break const correctness. The concerns about making the change were 1) it is user detectable (although only in boundary cases), 2) it changes a large number of signatures, and 3) it seems more of a design issue that an out-and-out defect.

The LWG believes that this issue should be considered as part of a general review of const issues for the next revision of the standard. Also see issue 200.

### 181. make_pair() unintended behavior

Section: 20.3.4 [pairs] Status: TC1 Submitter: Andrew Koenig Opened: 1999-08-03 Last modified: 2008-09-26

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Discussion:

The claim has surfaced in Usenet that expressions such as
`make_pair("abc", 3)`
are illegal, notwithstanding their use in examples, because template instantiation tries to bind the first template parameter to `const char (&)[4]`, which type is uncopyable.
I doubt anyone intended that behavior...

Proposed resolution:

In 20.3 [utility], paragraph 1 change the following declaration of make_pair():

>     template <class T1, class T2> pair<T1,T2> make_pair(const T1&, const T2&);

to:

>     template <class T1, class T2> pair<T1,T2> make_pair(T1, T2);

In 20.3.4 [pairs] paragraph 7 and the line before, change:

>     template <class T1, class T2>
>     pair<T1, T2> make_pair(const T1& x, const T2& y);

to:

>     template <class T1, class T2>
>     pair<T1, T2> make_pair(T1 x, T2 y);

and add the following footnote to the effects clause:

> According to 12.8 [class.copy], an implementation is permitted to not perform a copy of an argument, thus avoiding unnecessary copies.

Rationale:

Two potential fixes were suggested by Matt Austern and Dietmar Kühl, respectively, 1) overloading with array arguments, and 2) use of a reference_traits class with a specialization for arrays. Andy Koenig suggested changing to pass by value. In discussion, it appeared that this was a much smaller change to the standard that the other two suggestions, and any efficiency concerns were more than offset by the advantages of the solution. Two implementors reported that the proposed resolution passed their test suites.

### 182. Ambiguous references to size_t

Section: 17 [library] Status: CD1 Submitter: Al Stevens Opened: 1999-08-15 Last modified: 2008-09-26

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Discussion:

Many references to `size_t` throughout the document omit the `std::` namespace qualification.

For example, 17.6.3.6 [replacement.functions] paragraph 2:

>      operator new(size_t)
>      operator new(size_t, const std::nothrow_t&)
>      operator new[](size_t)
>      operator new[](size_t, const std::nothrow_t&)

Proposed resolution:

In 17.6.3.6 [replacement.functions] paragraph 2: replace:

> `- operator new(size_t)
> - operator new(size_t, const std::nothrow_t&)
> - operator new[](size_t)
> - operator new[](size_t, const std::nothrow_t&)`

by:

>     - operator new(std::size_t)
>     - operator new(std::size_t, const std::nothrow_t&)
>     - operator new[](std::size_t)
>     - operator new[](std::size_t, const std::nothrow_t&)

In [lib.allocator.requirements] 20.1.5, paragraph 4: replace:

> The typedef members pointer, const_pointer, size_type, and difference_type are required to be T*, T const*, size_t, and ptrdiff_t, respectively.

by:

> The typedef members pointer, const_pointer, size_type, and difference_type are required to be T*, T const*, std::size_t, and std::ptrdiff_t, respectively.

In [lib.allocator.members] 20.4.1.1, paragraphs 3 and 6: replace:

> 3 Notes: Uses ::operator new(size_t) (18.4.1).

> 6 Note: the storage is obtained by calling ::operator new(size_t), but it is unspecified when or how often this function is called. The use of hint is unspecified, but intended as an aid to locality if an implementation so desires.

by:

> 3 Notes: Uses ::operator new(std::size_t) (18.4.1).

> 6 Note: the storage is obtained by calling ::operator new(std::size_t), but it is unspecified when or how often this function is called. The use of hint is unspecified, but intended as an aid to locality if an implementation so desires.

In [lib.char.traits.require] 21.1.1, paragraph 1: replace:

> In Table 37, X denotes a Traits class defining types and functions for the character container type CharT; c and d denote values of type CharT; p and q denote values of type const CharT*; s denotes a value of type CharT*; n, i and j denote values of type size_t; e and f denote values of type X::int_type; pos denotes a value of type X::pos_type; and state denotes a value of type X::state_type.

by:

> In Table 37, X denotes a Traits class defining types and functions for the character container type CharT; c and d denote values of type CharT; p and q denote values of type const CharT*; s denotes a value of type CharT*; n, i and j denote values of type std::size_t; e and f denote values of type X::int_type; pos denotes a value of type X::pos_type; and state denotes a value of type X::state_type.

In [lib.char.traits.require] 21.1.1, table 37: replace the return type of X::length(p): "size_t" by "std::size_t".

In [lib.std.iterator.tags] 24.3.3, paragraph 2: replace:
typedef ptrdiff_t difference_type;
by:
typedef std::ptrdiff_t difference_type;

In [lib.locale.ctype] 22.2.1.1 put namespace std { ...} around the declaration of template <class charT> class ctype.
In [lib.iterator.traits] 24.3.1, paragraph 2 put namespace std { ...} around the declaration of:
template<class Iterator> struct iterator_traits
template<class T> struct iterator_traits<T*>
template<class T> struct iterator_traits<const T*>

Rationale:

The LWG believes correcting names like `size_t` and `ptrdiff_t` to `std::size_t` and `std::ptrdiff_t` to be essentially editorial. There there can't be another size_t or ptrdiff_t meant anyway because, according to 17.6.3.3.4 [extern.types],

> For each type T from the Standard C library, the types ::T and std::T are reserved to the implementation and, when defined, ::T shall be identical to std::T.

The issue is treated as a Defect Report to make explicit the Project Editor's authority to make this change.

[Post-Tokyo: Nico Josuttis provided the above wording at the request of the LWG.]

[Toronto: This is tangentially related to issue 229, but only tangentially: the intent of this issue is to address use of the name `size_t` in contexts outside of namespace std, such as in the description of `::operator new`. The proposed changes should be reviewed to make sure they are correct.]

[pre-Copenhagen: Nico has reviewed the changes and believes them to be correct.]

### 183. I/O stream manipulators don't work for wide character streams

Section: 27.7.3 [std.manip] Status: CD1 Submitter: Andy Sawyer Opened: 1999-07-07 Last modified: 2008-09-26

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Discussion:

27.7.3 [std.manip] paragraph 3 says (clause numbering added for exposition):

> Returns: An object s of unspecified type such that if [1] out is an (instance of) basic_ostream then the expression out<<s behaves as if f(s) were called, and if [2] in is an (instance of) basic_istream then the expression in>>s behaves as if f(s) were called. Where f can be defined as: ios_base& f(ios_base& str, ios_base::fmtflags mask) { // reset specified flags str.setf(ios_base::fmtflags(0), mask); return str; } [3] The expression out<<s has type ostream& and value out. [4] The expression in>>s has type istream& and value in.

Given the definitions [1] and [2] for out and in, surely [3] should read: "The expression out << s has type basic_ostream& ..." and [4] should read: "The expression in >> s has type basic_istream& ..."

If the wording in the standard is correct, I can see no way of implementing any of the manipulators so that they will work with wide character streams.

e.g. wcout << setbase( 16 );

Must have value 'wcout' (which makes sense) and type 'ostream&' (which doesn't).

The same "cut'n'paste" type also seems to occur in Paras 4,5,7 and 8. In addition, Para 6 [setfill] has a similar error, but relates only to ostreams.

I'd be happier if there was a better way of saying this, to make it clear that the value of the expression is "the same specialization of basic_ostream as out"&

Proposed resolution:

Replace section 27.7.3 [std.manip] except paragraph 1 with the following:

> 2- The type designated smanip in each of the following function descriptions is implementation-specified and may be different for each function.
> `smanip resetiosflags(ios_base::fmtflags mask);`
> -3- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves as if f(s, mask) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, mask) were called. The function f can be defined as:*
> [Footnote: The expression cin >> resetiosflags(ios_base::skipws) clears ios_base::skipws in the format flags stored in the basic_istream<charT,traits> object cin (the same as cin >> noskipws), and the expression cout << resetiosflags(ios_base::showbase) clears ios_base::showbase in the format flags stored in the basic_ostream<charT,traits> object cout (the same as cout << noshowbase). --- end footnote]
> `ios_base& f(ios_base& str, ios_base::fmtflags mask)
> {
> // reset specified flags
> str.setf(ios_base::fmtflags(0), mask);
> return str;
> }
> `
> The expression out<<s has type basic_ostream<charT,traits>& and value out. The expression in>>s has type basic_istream<charT,traits>& and value in.
> `smanip setiosflags(ios_base::fmtflags mask);`
> -4- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves as if f(s, mask) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, mask) were called. The function f can be defined as:
> `ios_base& f(ios_base& str, ios_base::fmtflags mask)
> {
> // set specified flags
> str.setf(mask);
> return str;
> }
> `
> The expression out<<s has type basic_ostream<charT,traits>& and value out. The expression in>>s has type basic_istream<charT,traits>& and value in.
> `smanip setbase(int base);`
> -5- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves as if f(s, base) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, base) were called. The function f can be defined as:
> `ios_base& f(ios_base& str, int base)
> {
> // set basefield
> str.setf(base == 8 ? ios_base::oct :
> base == 10 ? ios_base::dec :
> base == 16 ? ios_base::hex :
> ios_base::fmtflags(0), ios_base::basefield);
> return str;
> }
> `
> The expression out<<s has type basic_ostream<charT,traits>& and value out. The expression in>>s has type basic_istream<charT,traits>& and value in.
> `smanip setfill(char_type c);
> `
> -6- Returns: An object s of unspecified type such that if out is (or is derived from) basic_ostream<charT,traits> and c has type charT then the expression out<<s behaves as if f(s, c) were called. The function f can be defined as:
> `template<class charT, class traits>
> basic_ios<charT,traits>& f(basic_ios<charT,traits>& str, charT c)
> {
> // set fill character
> str.fill(c);
> return str;
> }
> `
> The expression out<<s has type basic_ostream<charT,traits>& and value out.
> `smanip setprecision(int n);`
> -7- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves as if f(s, n) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, n) were called. The function f can be defined as:
> `ios_base& f(ios_base& str, int n)
> {
> // set precision
> str.precision(n);
> return str;
> }
> `
> The expression out<<s has type basic_ostream<charT,traits>& and value out. The expression in>>s has type basic_istream<charT,traits>& and value in
> .
> `smanip setw(int n);
> `
> -8- Returns: An object s of unspecified type such that if out is an instance of basic_ostream<charT,traits> then the expression out<<s behaves as if f(s, n) were called, or if in is an instance of basic_istream<charT,traits> then the expression in>>s behaves as if f(s, n) were called. The function f can be defined as:
> `ios_base& f(ios_base& str, int n)
> {
> // set width
> str.width(n);
> return str;
> }
> `
> The expression out<<s has type basic_ostream<charT,traits>& and value out. The expression in>>s has type basic_istream<charT,traits>& and value in.

[Kona: Andy Sawyer and Beman Dawes will work to improve the wording of the proposed resolution.]

[Tokyo - The LWG noted that issue 216 involves the same paragraphs.]

[Post-Tokyo: The issues list maintainer combined the proposed resolution of this issue with the proposed resolution for issue 216 as they both involved the same paragraphs, and were so intertwined that dealing with them separately appear fraught with error. The full text was supplied by Bill Plauger; it was cross checked against changes supplied by Andy Sawyer. It should be further checked by the LWG.]

### 184. numeric_limits<bool> wording problems

Section: 18.3.1.5 [numeric.special] Status: CD1 Submitter: Gabriel Dos Reis Opened: 1999-07-21 Last modified: 2008-09-26

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Discussion:

bools are defined by the standard to be of integer types, as per 3.9.1 [basic.fundamental] paragraph 7. However "integer types" seems to have a special meaning for the author of 18.2. The net effect is an unclear and confusing specification for numeric_limits<bool> as evidenced below.

18.2.1.2/7 says numeric_limits<>::digits is, for built-in integer types, the number of non-sign bits in the representation.

4.5/4 states that a bool promotes to int ; whereas 4.12/1 says any non zero arithmetical value converts to true.

I don't think it makes sense at all to require numeric_limits<bool>::digits and numeric_limits<bool>::digits10 to be meaningful.

The standard defines what constitutes a signed (resp. unsigned) integer types. It doesn't categorize bool as being signed or unsigned. And the set of values of bool type has only two elements.

I don't think it makes sense to require numeric_limits<bool>::is_signed to be meaningful.

18.2.1.2/18 for numeric_limits<integer_type>::radix says:

> For integer types, specifies the base of the representation.186)

This disposition is at best misleading and confusing for the standard requires a "pure binary numeration system" for integer types as per 3.9.1/7

The footnote 186) says: "Distinguishes types with base other than 2 (e.g BCD)." This also erroneous as the standard never defines any integer types with base representation other than 2.

Furthermore, numeric_limits<bool>::is_modulo and numeric_limits<bool>::is_signed have similar problems.

Proposed resolution:

Append to the end of 18.3.1.5 [numeric.special]:

> The specialization for bool shall be provided as follows:

>         namespace std {
>            template<> class numeric_limits<bool> {
>            public:
>              static const bool is_specialized = true;
>              static bool min() throw() { return false; }
>              static bool max() throw() { return true; }

>              static const int  digits = 1;
>              static const int  digits10 = 0;
>              static const bool is_signed = false;
>              static const bool is_integer = true;
>              static const bool is_exact = true;
>              static const int  radix = 2;
>              static bool epsilon() throw() { return 0; }
>              static bool round_error() throw() { return 0; }

>              static const int  min_exponent = 0;
>              static const int  min_exponent10 = 0;
>              static const int  max_exponent = 0;
>              static const int  max_exponent10 = 0;

>              static const bool has_infinity = false;
>              static const bool has_quiet_NaN = false;
>              static const bool has_signaling_NaN = false;
>              static const float_denorm_style has_denorm = denorm_absent;
>              static const bool has_denorm_loss = false;
>              static bool infinity() throw() { return 0; }
>              static bool quiet_NaN() throw() { return 0; }
>              static bool signaling_NaN() throw() { return 0; }
>              static bool denorm_min() throw() { return 0; }

>              static const bool is_iec559 = false;
>              static const bool is_bounded = true;
>              static const bool is_modulo = false;

>              static const bool traps = false;
>              static const bool tinyness_before = false;
>              static const float_round_style round_style = round_toward_zero;
>            };
>          }

[Tokyo: The LWG desires wording that specifies exact values rather than more general wording in the original proposed resolution.]

[Post-Tokyo: At the request of the LWG in Tokyo, Nico Josuttis provided the above wording.]

### 185. Questionable use of term "inline"

Section: 20.7 [function.objects] Status: CD1 Submitter: UK Panel Opened: 1999-07-26 Last modified: 2008-09-26

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Discussion:

Paragraph 4 of 20.7 [function.objects] says:

> [Example: To negate every element of a: transform(a.begin(), a.end(), a.begin(), negate<double>()); The corresponding functions will inline the addition and the negation. end example]

(Note: The "addition" referred to in the above is in para 3) we can find no other wording, except this (non-normative) example which suggests that any "inlining" will take place in this case.

Indeed both:

> 17.4.4.3 Global Functions [lib.global.functions] 1 It is unspecified whether any global functions in the C++ Standard Library are defined as inline (7.1.2).

and

> 17.4.4.4 Member Functions [lib.member.functions] 1 It is unspecified whether any member functions in the C++ Standard Library are defined as inline (7.1.2).

take care to state that this may indeed NOT be the case.

Thus the example "mandates" behavior that is explicitly not required elsewhere.

Proposed resolution:

In 20.7 [function.objects] paragraph 1, remove the sentence:

> They are important for the effective use of the library.

Remove 20.7 [function.objects] paragraph 2, which reads:

> Using function objects together with function templates increases the expressive power of the library as well as making the resulting code much more efficient.

In 20.7 [function.objects] paragraph 4, remove the sentence:

> The corresponding functions will inline the addition and the negation.

[Kona: The LWG agreed there was a defect.]

[Tokyo: The LWG crafted the proposed resolution.]

### 186. bitset::set() second parameter should be bool

Section: 20.3.7.2 [bitset.members] Status: CD1 Submitter: Darin Adler Opened: 1999-08-13 Last modified: 2008-09-26

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Discussion:

In section 20.3.7.2 [bitset.members], paragraph 13 defines the bitset::set operation to take a second parameter of type int. The function tests whether this value is non-zero to determine whether to set the bit to true or false. The type of this second parameter should be bool. For one thing, the intent is to specify a Boolean value. For another, the result type from test() is bool. In addition, it's possible to slice an integer that's larger than an int. This can't happen with bool, since conversion to bool has the semantic of translating 0 to false and any non-zero value to true.

Proposed resolution:

In 20.3.7 [template.bitset] Para 1 Replace:

>     bitset<N>& set(size_t pos, int val = true );

With:

>     bitset<N>& set(size_t pos, bool val = true );

In 20.3.7.2 [bitset.members] Para 12(.5) Replace:

>     bitset<N>& set(size_t pos, int val = 1 );

With:

>     bitset<N>& set(size_t pos, bool val = true );

[Kona: The LWG agrees with the description. Andy Sawyer will work on better P/R wording.]

[Post-Tokyo: Andy provided the above wording.]

Rationale:

`bool` is a better choice. It is believed that binary compatibility is not an issue, because this member function is usually implemented as `inline`, and because it is already the case that users cannot rely on the type of a pointer to a nonvirtual member of a standard library class.

### 187. iter_swap underspecified

Section: 25.3.3 [alg.swap] Status: CD1 Submitter: Andrew Koenig Opened: 1999-08-14 Last modified: 2008-09-26

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Discussion:

The description of iter_swap in 25.2.2 paragraph 7,says that it ``exchanges the values'' of the objects to which two iterators refer.
What it doesn't say is whether it does so using swap or using the assignment operator and copy constructor.
This question is an important one to answer, because swap is specialized to work efficiently for standard containers.
For example:

>     vector<int> v1, v2;
>     iter_swap(&v1, &v2);

Is this call to iter_swap equivalent to calling swap(v1, v2)? Or is it equivalent to

>     {
>     vector<int> temp = v1;
>     v1 = v2;
>     v2 = temp;
>     }

The first alternative is O(1); the second is O(n).

A LWG member, Dave Abrahams, comments:

> Not an objection necessarily, but I want to point out the cost of that requirement:

> > `iter_swap(list<T>::iterator, list<T>::iterator)`

> can currently be specialized to be more efficient than iter_swap(T*,T*) for many T (by using splicing). Your proposal would make that optimization illegal.

[Kona: The LWG notes the original need for iter_swap was proxy iterators which are no longer permitted.]

Proposed resolution:

Change the effect clause of iter_swap in 25.2.2 paragraph 7 from:

> Exchanges the values pointed to by the two iterators a and b.

to

> `swap(*a, *b)`.

Rationale:

It's useful to say just what `iter_swap` does. There may be some iterators for which we want to specialize `iter_swap`, but the fully general version should have a general specification.

Note that in the specific case of `list<T>::iterator`, iter_swap should not be specialized as suggested above. That would do much more than exchanging the two iterators' values: it would change predecessor/successor relationships, possibly moving the iterator from one list to another. That would surely be inappropriate.

### 189. setprecision() not specified correctly

Section: 27.5.2.2 [fmtflags.state] Status: TC1 Submitter: Andrew Koenig Opened: 1999-08-25 Last modified: 2008-09-26

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Discussion:

27.4.2.2 paragraph 9 claims that setprecision() sets the precision, and includes a parenthetical note saying that it is the number of digits after the decimal point.
This claim is not strictly correct. For example, in the default floating-point output format, setprecision sets the number of significant digits printed, not the number of digits after the decimal point.
I would like the committee to look at the definition carefully and correct the statement in 27.4.2.2

Proposed resolution:

Remove from 27.5.2.2 [fmtflags.state], paragraph 9, the text "(number of digits after the decimal point)".

### 193. Heap operations description incorrect

Section: 25.4.6 [alg.heap.operations] Status: TC1 Submitter: Markus Mauhart Opened: 1999-09-24 Last modified: 2008-09-26

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Duplicate of: 216

Discussion:

25.3.6 [lib.alg.heap.operations] states two key properties of a heap [a,b), the first of them is
`"(1) *a is the largest element"
I think this is incorrect and should be changed to the wording in the proposed resolution.

Actually there are two independent changes:

> A-"part of largest equivalence class" instead of "largest", cause 25.3 [lib.alg.sorting] asserts "strict weak ordering" for all its sub clauses.

> B-Take 'an oldest' from that equivalence class, otherwise the heap functions could not be used for a priority queue as explained in 23.2.3.2.2 [lib.priqueue.members] (where I assume that a "priority queue" respects priority AND time).

Proposed resolution:

Change 25.4.6 [alg.heap.operations] property (1) from:

> (1) *a is the largest element

to:

> (1) There is no element greater than `*a`

### 195. Should `basic_istream::sentry`'s constructor ever set eofbit?

Section: 27.7.1.1.3 [istream::sentry] Status: TC1 Submitter: Matt Austern Opened: 1999-10-13 Last modified: 2008-09-26

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Discussion:

Suppose that `is.flags() & ios_base::skipws` is nonzero. What should `basic_istream<>::sentry`'s constructor do if it reaches eof while skipping whitespace? 27.6.1.1.2/5 suggests it should set failbit. Should it set eofbit as well? The standard doesn't seem to answer that question.

On the one hand, nothing in 27.7.1.1.3 [istream::sentry] says that `basic_istream<>::sentry` should ever set eofbit. On the other hand, 27.7.1.1 [istream] paragraph 4 says that if extraction from a `streambuf` "returns `traits::eof()`, then the input function, except as explicitly noted otherwise, completes its actions and does `setstate(eofbit)"`. So the question comes down to whether `basic_istream<>::sentry`'s constructor is an input function.

Comments from Jerry Schwarz:

> It was always my intention that eofbit should be set any time that a virtual returned something to indicate eof, no matter what reason iostream code had for calling the virtual.

> The motivation for this is that I did not want to require streambufs to behave consistently if their virtuals are called after they have signaled eof.

> The classic case is a streambuf reading from a UNIX file. EOF isn't really a state for UNIX file descriptors. The convention is that a read on UNIX returns 0 bytes to indicate "EOF", but the file descriptor isn't shut down in any way and future reads do not necessarily also return 0 bytes. In particular, you can read from tty's on UNIX even after they have signaled "EOF". (It isn't always understood that a ^D on UNIX is not an EOF indicator, but an EOL indicator. By typing a "line" consisting solely of ^D you cause a read to return 0 bytes, and by convention this is interpreted as end of file.)

Proposed resolution:

Add a sentence to the end of 27.6.1.1.2 paragraph 2:

> If `is.rdbuf()->sbumpc()` or `is.rdbuf()->sgetc()` returns `traits::eof()`, the function calls `setstate(failbit | eofbit)` (which may throw `ios_base::failure`).

### 198. Validity of pointers and references unspecified after iterator destruction

Section: X [iterator.concepts] Status: CD1 Submitter: Beman Dawes Opened: 1999-11-03 Last modified: 2008-09-30

View all other issues in [iterator.concepts].

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Discussion:

Is a pointer or reference obtained from an iterator still valid after destruction of the iterator?

Is a pointer or reference obtained from an iterator still valid after the value of the iterator changes?

>     #include <iostream>
>     #include <vector>
>     #include <iterator>

>     int main()
>     {
>         typedef std::vector<int> vec_t;
>         vec_t v;
>         v.push_back( 1 );

>         // Is a pointer or reference obtained from an iterator still
>         // valid after destruction of the iterator?
>         int * p = &*v.begin();
>         std::cout << *p << '\n';  // OK?

>         // Is a pointer or reference obtained from an iterator still
>         // valid after the value of the iterator changes?
>         vec_t::iterator iter( v.begin() );
>         p = &*iter++;
>         std::cout << *p << '\n';  // OK?

>         return 0;
>     }

The standard doesn't appear to directly address these questions. The standard needs to be clarified. At least two real-world cases have been reported where library implementors wasted considerable effort because of the lack of clarity in the standard. The question is important because requiring pointers and references to remain valid has the effect for practical purposes of prohibiting iterators from pointing to cached rather than actual elements of containers.

The standard itself assumes that pointers and references obtained from an iterator are still valid after iterator destruction or change. The definition of reverse_iterator::operator*(), 24.5.1.3.3 [reverse.iter.conv], which returns a reference, defines effects:

>     Iterator tmp = current;
>     return *--tmp;

The definition of reverse_iterator::operator->(), 24.5.1.3.4 [reverse.iter.op.star], which returns a pointer, defines effects:

>     return &(operator*());

Because the standard itself assumes pointers and references remain valid after iterator destruction or change, the standard should say so explicitly. This will also reduce the chance of user code breaking unexpectedly when porting to a different standard library implementation.

Proposed resolution:

Add a new paragraph to X [iterator.concepts]:

> Destruction of an iterator may invalidate pointers and references previously obtained from that iterator.

Replace paragraph 1 of 24.5.1.3.3 [reverse.iter.conv] with:

> Effects:

>       this->tmp = current;
>       --this->tmp;
>       return *this->tmp;

> [Note: This operation must use an auxiliary member variable, rather than a temporary variable, to avoid returning a reference that persists beyond the lifetime of its associated iterator. (See X [iterator.concepts].) The name of this member variable is shown for exposition only. --end note]

[Post-Tokyo: The issue has been reformulated purely in terms of iterators.]

[Pre-Toronto: Steve Cleary pointed out the no-invalidation assumption by reverse_iterator. The issue and proposed resolution was reformulated yet again to reflect this reality.]

[Copenhagen: Steve Cleary pointed out that reverse_iterator assumes its underlying iterator has persistent pointers and references. Andy Koenig pointed out that it is possible to rewrite reverse_iterator so that it no longer makes such an assupmption. However, this issue is related to issue 299. If we decide it is intentional that `p[n]` may return by value instead of reference when `p` is a Random Access Iterator, other changes in reverse_iterator will be necessary.]

Rationale:

This issue has been discussed extensively. Note that it is not an issue about the behavior of predefined iterators. It is asking whether or not user-defined iterators are permitted to have transient pointers and references. Several people presented examples of useful user-defined iterators that have such a property; examples include a B-tree iterator, and an "iota iterator" that doesn't point to memory. Library implementors already seem to be able to cope with such iterators: they take pains to avoid forming references to memory that gets iterated past. The only place where this is a problem is `reverse_iterator`, so this issue changes `reverse_iterator` to make it work.

This resolution does not weaken any guarantees provided by predefined iterators like `list<int>::iterator`. Clause 23 should be reviewed to make sure that guarantees for predefined iterators are as strong as users expect.

### 199. What does `allocate(0)` return?

Section: 20.2.2 [allocator.requirements] Status: TC1 Submitter: Matt Austern Opened: 1999-11-19 Last modified: 2008-09-26

View all other issues in [allocator.requirements].

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Discussion:

Suppose that `A` is a class that conforms to the Allocator requirements of Table 32, and `a` is an object of class `A` What should be the return value of `a.allocate(0)`? Three reasonable possibilities: forbid the argument `0`, return a null pointer, or require that the return value be a unique non-null pointer.

Proposed resolution:

Add a note to the `allocate` row of Table 32: "[Note: If `n == 0`, the return value is unspecified. --end note]"

Rationale:

A key to understanding this issue is that the ultimate use of allocate() is to construct an iterator, and that iterator for zero length sequences must be the container's past-the-end representation. Since this already implies special case code, it would be over-specification to mandate the return value.

### 200. Forward iterator requirements don't allow constant iterators

Section: 24.2.3 [forward.iterators] Status: CD1 Submitter: Matt Austern Opened: 1999-11-19 Last modified: 2008-09-26

View all other issues in [forward.iterators].

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Discussion:

In table 74, the return type of the expression `*a` is given as `T&`, where `T` is the iterator's value type. For constant iterators, however, this is wrong. ("Value type" is never defined very precisely, but it is clear that the value type of, say, `std::list<int>::const_iterator` is supposed to be `int`, not `const int`.)

Proposed resolution:

In table 74, in the `*a` and `*r++` rows, change the return type from "`T&`" to "`T&` if `X` is mutable, otherwise `const T&`". In the `a->m` row, change the return type from "`U&`" to "`U&` if `X` is mutable, otherwise `const U&`".

[Tokyo: The LWG believes this is the tip of a larger iceberg; there are multiple const problems with the STL portion of the library and that these should be addressed as a single package. Note that issue 180 has already been declared NAD Future for that very reason.]

[Redmond: the LWG thinks this is separable from other constness issues. This issue is just cleanup; it clarifies language that was written before we had iterator_traits. Proposed resolution was modified: the original version only discussed *a. It was pointed out that we also need to worry about *r++ and a->m.]

### 201. Numeric limits terminology wrong

Section: 18.3.1 [limits] Status: CD1 Submitter: Stephen Cleary Opened: 1999-12-21 Last modified: 2008-09-26

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Discussion:

In some places in this section, the terms "fundamental types" and "scalar types" are used when the term "arithmetic types" is intended. The current usage is incorrect because void is a fundamental type and pointers are scalar types, neither of which should have specializations of numeric_limits.

[Lillehammer: it remains true that numeric_limits is using imprecise language. However, none of the proposals for changed wording are clearer. A redesign of numeric_limits is needed, but this is more a task than an open issue.]

Proposed resolution:

Change 18.3 [support.limits] to:

> -1- The headers `<limits>`, `<climits>`, `<cfloat>`, and `<cinttypes>` supply characteristics of implementation-dependent fundamental arithmetic types (3.9.1).

Change 18.3.1 [limits] to:

> -1- The `numeric_limits` component provides a C++ program with information about various properties of the implementation's representation of the fundamental arithmetic types.

> -2- Specializations shall be provided for each fundamental arithmetic type, both floating point and integer, including `bool`. The member `is_specialized` shall be `true` for all such specializations of `numeric_limits`.

> -4- Non-fundamental arithmetic standard types, such as `complex<T>` (26.3.2), shall not have specializations.

Change 18.3.1.1 [numeric.limits] to:

> -1- The member `is_specialized` makes it possible to distinguish between fundamental types, which have specializations, and non-scalar types, which do not.

### 202. unique() effects unclear when predicate not an equivalence relation

Section: 25.3.9 [alg.unique] Status: CD1 Submitter: Andrew Koenig Opened: 2000-01-13 Last modified: 2008-09-26

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Discussion:

What should unique() do if you give it a predicate that is not an equivalence relation? There are at least two plausible answers:

> 1. You can't, because 25.2.8 says that it it "eliminates all but the first element from every consecutive group of equal elements..." and it wouldn't make sense to interpret "equal" as meaning anything but an equivalence relation. [It also doesn't make sense to interpret "equal" as meaning ==, because then there would never be any sense in giving a predicate as an argument at all.]

> 2. The word "equal" should be interpreted to mean whatever the predicate says, even if it is not an equivalence relation (and in particular, even if it is not transitive).

The example that raised this question is from Usenet:

>     int f[] = { 1, 3, 7, 1, 2 };
>     int* z = unique(f, f+5, greater<int>());

If one blindly applies the definition using the predicate greater<int>, and ignore the word "equal", you get:

> Eliminates all but the first element from every consecutive group of elements referred to by the iterator i in the range [first, last) for which *i > *(i - 1).

The first surprise is the order of the comparison. If we wanted to allow for the predicate not being an equivalence relation, then we should surely compare elements the other way: pred(*(i - 1), *i). If we do that, then the description would seem to say: "Break the sequence into subsequences whose elements are in strictly increasing order, and keep only the first element of each subsequence". So the result would be 1, 1, 2. If we take the description at its word, it would seem to call for strictly DEcreasing order, in which case the result should be 1, 3, 7, 2.
In fact, the SGI implementation of unique() does neither: It yields 1, 3, 7.

Proposed resolution:

Change 25.3.9 [alg.unique] paragraph 1 to:

> For a nonempty range, eliminates all but the first element from every consecutive group of equivalent elements referred to by the iterator `i` in the range [first+1, last) for which the following conditions hold: `*(i-1) == *i` or `pred(*(i-1), *i) != false`.

Also insert a new paragraph, paragraph 2a, that reads: "Requires: The comparison function must be an equivalence relation."

[Redmond: discussed arguments for and against requiring the comparison function to be an equivalence relation. Straw poll: 14-2-5. First number is to require that it be an equivalence relation, second number is to explicitly not require that it be an equivalence relation, third number is people who believe they need more time to consider the issue. A separate issue: Andy Sawyer pointed out that "i-1" is incorrect, since "i" can refer to the first iterator in the range. Matt provided wording to address this problem.]

[Curaçao: The LWG changed "... the range (first, last)..." to "... the range [first+1, last)..." for clarity. They considered this change close enough to editorial to not require another round of review.]

Rationale:

The LWG also considered an alternative resolution: change 25.3.9 [alg.unique] paragraph 1 to:

> For a nonempty range, eliminates all but the first element from every consecutive group of elements referred to by the iterator `i` in the range (first, last) for which the following conditions hold: `*(i-1) == *i` or `pred(*(i-1), *i) != false`.

Also insert a new paragraph, paragraph 1a, that reads: "Notes: The comparison function need not be an equivalence relation."

Informally: the proposed resolution imposes an explicit requirement that the comparison function be an equivalence relation. The alternative resolution does not, and it gives enough information so that the behavior of unique() for a non-equivalence relation is specified. Both resolutions are consistent with the behavior of existing implementations.

### 206. operator new(size_t, nothrow) may become unlinked to ordinary operator new if ordinary version replaced

Section: 18.6.1.1 [new.delete.single] Status: CD1 Submitter: Howard Hinnant Opened: 1999-08-29 Last modified: 2008-09-26

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Discussion:

As specified, the implementation of the nothrow version of operator new does not necessarily call the ordinary operator new, but may instead simply call the same underlying allocator and return a null pointer instead of throwing an exception in case of failure.

Such an implementation breaks code that replaces the ordinary version of new, but not the nothrow version. If the ordinary version of new/delete is replaced, and if the replaced delete is not compatible with pointers returned from the library versions of new, then when the replaced delete receives a pointer allocated by the library new(nothrow), crash follows.

The fix appears to be that the lib version of new(nothrow) must call the ordinary new. Thus when the ordinary new gets replaced, the lib version will call the replaced ordinary new and things will continue to work.

An alternative would be to have the ordinary new call new(nothrow). This seems sub-optimal to me as the ordinary version of new is the version most commonly replaced in practice. So one would still need to replace both ordinary and nothrow versions if one wanted to replace the ordinary version.

Another alternative is to put in clear text that if one version is replaced, then the other must also be replaced to maintain compatibility. Then the proposed resolution below would just be a quality of implementation issue. There is already such text in paragraph 7 (under the new(nothrow) version). But this nuance is easily missed if one reads only the paragraphs relating to the ordinary new.

N2158 has been written explaining the rationale for the proposed resolution below.

Proposed resolution:

Change 18.5.1.1 [new.delete.single]:

>     void* operator new(std::size_t size, const std::nothrow_t&) throw();

> > -5- Effects: Same as above, except that it is called by a placement version of a new-expression when a C++ program prefers a null pointer result as an error indication, instead of a `bad_alloc` exception.

> > -6- Replaceable: a C++ program may define a function with this function signature that displaces the default version defined by the C++ Standard library.

> > -7- Required behavior: Return a non-null pointer to suitably aligned storage (3.7.4), or else return a null pointer. This nothrow version of operator new returns a pointer obtained as if acquired from the (possibly replaced) ordinary version. This requirement is binding on a replacement version of this function.

> > -8- Default behavior:

> > - Calls `operator new(size)`.
> > - If the call to `operator new(size)` returns normally, returns the result of that call, else
> > - if the call to `operator new(size)` throws an exception, returns a null pointer.
> > - Executes a loop: Within the loop, the function first attempts to allocate the requested storage. Whether the attempt involves a call to the Standard C library function `malloc` is unspecified.
> > - Returns a pointer to the allocated storage if the attempt is successful. Otherwise, if the last argument to `set_new_handler()` was a null pointer, return a null pointer.
> > - Otherwise, the function calls the current new_handler (18.5.2.2). If the called function returns, the loop repeats.
> > - The loop terminates when an attempt to allocate the requested storage is successful or when a called new_handler function does not return. If the called new_handler function terminates by throwing a `bad_alloc exception`, the function returns a null pointer.

> > -9- [Example:

> > >     T* p1 = new T;                 // throws bad_alloc if it fails
> > >     T* p2 = new(nothrow) T;        // returns 0 if it fails

> > --end example]

>     void operator delete(void* ptr) throw();
>     void operator delete(void* ptr, const std::nothrow_t&) throw();

> > -10- Effects: The deallocation function (3.7.4.2) called by a delete-expression to render the value of `ptr` invalid.

> > -11- Replaceable: a C++ program may define a function with this function signature that displaces the default version defined by the C++ Standard library.

> > -12- Requires: the value of `ptr` is null or the value returned by an earlier call to the default (possibly replaced) `operator new(std::size_t)` or `operator new(std::size_t, const std::nothrow_t&)`.

> > -13- Default behavior:

> > - For a null value of `ptr`, do nothing.
> > - Any other value of `ptr` shall be a value returned earlier by a call to the default `operator new`, which was not invalidated by an intervening call to `operator delete(void*)` (17.4.3.7). For such a non-null value of `ptr`, reclaims storage allocated by the earlier call to the default `operator new`.

> > -14- Remarks: It is unspecified under what conditions part or all of such reclaimed storage is allocated by a subsequent call to `operator new` or any of `calloc`, `malloc`, or `realloc`, declared in `<cstdlib>`.

>     void operator delete(void* ptr, const std::nothrow_t&) throw();

> > -15- Effects: Same as above, except that it is called by the implementation when an exception propagates from a nothrow placement version of the new-expression (i.e. when the constructor throws an exception).

> > -16- Replaceable: a C++ program may define a function with this function signature that displaces the default version defined by the C++ Standard library.

> > -17- Requires: the value of `ptr` is null or the value returned by an earlier call to the (possibly replaced) `operator new(std::size_t)` or `operator new(std::size_t, const std::nothrow_t&)`.

> > -18- Default behavior: Calls `operator delete(ptr)`.

Change 18.5.1.2 [new.delete.array]

>     void* operator new[](std::size_t size, const std::nothrow_t&) throw();

> > -5- Effects: Same as above, except that it is called by a placement version of a new-expression when a C++ program prefers a null pointer result as an error indication, instead of a `bad_alloc` exception.

> > -6- Replaceable: a C++ program can define a function with this function signature that displaces the default version defined by the C++ Standard library.

> > -7- Required behavior: Same as for operator `new(std::size_t, const std::nothrow_t&)`. This nothrow version of operator `new[]` returns a pointer obtained as if acquired from the ordinary version. Return a non-null pointer to suitably aligned storage (3.7.4), or else return a null pointer. This nothrow version of operator new returns a pointer obtained as if acquired from the (possibly replaced) `operator new[](std::size_t size)`. This requirement is binding on a replacement version of this function.

> > -8- Default behavior: Returns `operator new(size, nothrow)`.

> > - Calls `operator new[](size)`.
> > - If the call to `operator new[](size)` returns normally, returns the result of that call, else
> > - if the call to `operator new[](size)` throws an exception, returns a null pointer.

>     void operator delete[](void* ptr) throw();
>     void operator delete[](void* ptr, const std::nothrow_t&) throw();

> > -9- Effects: The deallocation function (3.7.4.2) called by the array form of a delete-expression to render the value of `ptr` invalid.

> > -10- Replaceable: a C++ program can define a function with this function signature that displaces the default version defined by the C++ Standard library.

> > -11- Requires: the value of `ptr` is null or the value returned by an earlier call to `operator new[](std::size_t)` or `operator new[](std::size_t, const std::nothrow_t&)`.

> > -12- Default behavior: Calls `operator delete(ptr)` or `operator delete[](ptr, std::nothrow)` respectively.

Rationale:

Yes, they may become unlinked, and that is by design. If a user replaces one, the user should also replace the other.

[ Reopened due to a gcc conversation between Howard, Martin and Gaby. Forwarding or not is visible behavior to the client and it would be useful for the client to know which behavior it could depend on. ]

[ Batavia: Robert voiced serious reservations about backwards compatibility for his customers. ]

### 208. Unnecessary restriction on past-the-end iterators

Section: X [iterator.concepts] Status: TC1 Submitter: Stephen Cleary Opened: 2000-02-02 Last modified: 2008-09-30

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Discussion:

In 24.1 paragraph 5, it is stated ". . . Dereferenceable and past-the-end values are always non-singular."

This places an unnecessary restriction on past-the-end iterators for containers with forward iterators (for example, a singly-linked list). If the past-the-end value on such a container was a well-known singular value, it would still satisfy all forward iterator requirements.

Removing this restriction would allow, for example, a singly-linked list without a "footer" node.

This would have an impact on existing code that expects past-the-end iterators obtained from different (generic) containers being not equal.

Proposed resolution:

Change X [iterator.concepts] paragraph 5, the last sentence, from:

> Dereferenceable and past-the-end values are always non-singular.

to:

> Dereferenceable values are always non-singular.

Rationale:

For some kinds of containers, including singly linked lists and zero-length vectors, null pointers are perfectly reasonable past-the-end iterators. Null pointers are singular.

### 209. basic_string declarations inconsistent

Section: 21.4 [basic.string] Status: TC1 Submitter: Igor Stauder Opened: 2000-02-11 Last modified: 2008-09-26

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Discussion:

In Section 21.4 [basic.string] the basic_string member function declarations use a consistent style except for the following functions:

>     void push_back(const charT);
>     basic_string& assign(const basic_string&);
>     void swap(basic_string<charT,traits,Allocator>&);

- push_back, assign, swap: missing argument name
- push_back: use of const with charT (i.e. POD type passed by value not by reference - should be charT or const charT& )
- swap: redundant use of template parameters in argument basic_string<charT,traits,Allocator>&

Proposed resolution:

In Section 21.4 [basic.string] change the basic_string member function declarations push_back, assign, and swap to:

>     void push_back(charT c);

>     basic_string& assign(const basic_string& str);
>     void swap(basic_string& str);

Rationale:

Although the standard is in general not consistent in declaration style, the basic_string declarations are consistent other than the above. The LWG felt that this was sufficient reason to merit the change.

### 210. distance first and last confused

Section: 25 [algorithms] Status: TC1 Submitter: Lisa Lippincott Opened: 2000-02-15 Last modified: 2008-09-26

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Discussion:

In paragraph 9 of section 25 [algorithms], it is written:

> In the description of the algorithms operators + and - are used for some of the iterator categories for which they do not have to be defined. In these cases the semantics of [...] a-b is the same as of
> `return distance(a, b);`

Proposed resolution:

On the last line of paragraph 9 of section 25 [algorithms] change `"a-b"` to `"b-a".`

Rationale:

There are two ways to fix the defect; change the description to b-a or change the return to distance(b,a). The LWG preferred the former for consistency.

### 211. operator>>(istream&, string&) doesn't set failbit

Section: 21.4.8.9 [string.io] Status: TC1 Submitter: Scott Snyder Opened: 2000-02-04 Last modified: 2008-09-26

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Discussion:

The description of the stream extraction operator for std::string (section 21.3.7.9 [lib.string.io]) does not contain a requirement that failbit be set in the case that the operator fails to extract any characters from the input stream.

This implies that the typical construction

>     std::istream is;
>     std::string str;
>     ...
>     while (is >> str) ... ;

(which tests failbit) is not required to terminate at EOF.

Furthermore, this is inconsistent with other extraction operators, which do include this requirement. (See sections 27.7.1.2 [istream.formatted] and 27.7.1.3 [istream.unformatted]), where this requirement is present, either explicitly or implicitly, for the extraction operators. It is also present explicitly in the description of getline (istream&, string&, charT) in section 21.4.8.9 [string.io] paragraph 8.)

Proposed resolution:

Insert new paragraph after paragraph 2 in section 21.4.8.9 [string.io]:

> If the function extracts no characters, it calls is.setstate(ios::failbit) which may throw ios_base::failure (27.4.4.3).

### 212. Empty range behavior unclear for several algorithms

Section: 25.4.7 [alg.min.max] Status: TC1 Submitter: Nico Josuttis Opened: 2000-02-26 Last modified: 2008-09-26

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Discussion:

The standard doesn't specify what min_element() and max_element() shall return if the range is empty (first equals last). The usual implementations return last. This problem seems also apply to partition(), stable_partition(), next_permutation(), and prev_permutation().

Proposed resolution:

In 25.4.7 [alg.min.max] - Minimum and maximum, paragraphs 7 and 9, append: Returns last if first==last.

Rationale:

The LWG looked in some detail at all of the above mentioned algorithms, but believes that except for min_element() and max_element() it is already clear that last is returned if first == last.

### 214. set::find() missing const overload

Section: 23.4.3 [set], 23.4.4 [multiset] Status: CD1 Submitter: Judy Ward Opened: 2000-02-28 Last modified: 2008-09-26

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Duplicate of: 450

Discussion:

The specification for the associative container requirements in Table 69 state that the find member function should "return iterator; const_iterator for constant a". The map and multimap container descriptions have two overloaded versions of find, but set and multiset do not, all they have is:

>     iterator find(const key_type & x) const;

Proposed resolution:

Change the prototypes for find(), lower_bound(), upper_bound(), and equal_range() in section 23.4.3 [set] and section 23.4.4 [multiset] to each have two overloads:

>     iterator find(const key_type & x);
>     const_iterator find(const key_type & x) const;

>     iterator lower_bound(const key_type & x);
>     const_iterator lower_bound(const key_type & x) const;

>     iterator upper_bound(const key_type & x);
>     const_iterator upper_bound(const key_type & x) const;

>     pair<iterator, iterator> equal_range(const key_type & x);
>     pair<const_iterator, const_iterator> equal_range(const key_type & x) const;

[Tokyo: At the request of the LWG, Judy Ward provided wording extending the proposed resolution to lower_bound, upper_bound, and equal_range.]

### 217. Facets example (Classifying Japanese characters) contains errors

Section: 22.4.8 [facets.examples] Status: TC1 Submitter: Martin Sebor Opened: 2000-02-29 Last modified: 2008-09-26

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Discussion:

The example in 22.2.8, paragraph 11 contains the following errors:

1) The member function `My::JCtype::is_kanji()' is non-const; the function must be const in order for it to be callable on a const object (a reference to which which is what std::use_facet<>() returns).

2) In file filt.C, the definition of `JCtype::id' must be qualified with the name of the namespace `My'.

3) In the definition of `loc' and subsequently in the call to use_facet<>() in main(), the name of the facet is misspelled: it should read `My::JCtype' rather than `My::JCType'.

Proposed resolution:

Replace the "Classifying Japanese characters" example in 22.2.8, paragraph 11 with the following:

    #include <locale>

    namespace My {
        using namespace std;
        class JCtype : public locale::facet {
        public:
            static locale::id id;     //  required for use as a new locale facet
            bool is_kanji (wchar_t c) const;
            JCtype() {}
        protected:
            ~JCtype() {}
        };
    }

    //  file:  filt.C
    #include <iostream>
    #include <locale>
    #include "jctype"                 //  above
    std::locale::id My::JCtype::id;   //  the static  JCtype  member
    declared above.

    int main()
    {
        using namespace std;
        typedef ctype<wchar_t> wctype;
        locale loc(locale(""),              //  the user's preferred locale...
                   new My::JCtype);         //  and a new feature ...
        wchar_t c = use_facet<wctype>(loc).widen('!');
        if (!use_facet<My::JCtype>(loc).is_kanji(c))
            cout << "no it isn't!" << endl;
        return 0;
    }

### 220. ~ios_base() usage valid?

Section: 27.5.2.7 [ios.base.cons] Status: TC1 Submitter: Jonathan Schilling, Howard Hinnant Opened: 2000-03-13 Last modified: 2008-09-26

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Discussion:

The pre-conditions for the ios_base destructor are described in 27.4.2.7 paragraph 2:

> Effects: Destroys an object of class ios_base. Calls each registered callback pair (fn,index) (27.4.2.6) as (*fn)(erase_event,*this,index) at such time that any ios_base member function called from within fn has well defined results.

But what is not clear is: If no callback functions were ever registered, does it matter whether the ios_base members were ever initialized?

For instance, does this program have defined behavior:

>     #include <ios>

>     class D : public std::ios_base { };

>     int main() { D d; }

It seems that registration of a callback function would surely affect the state of an ios_base. That is, when you register a callback function with an ios_base, the ios_base must record that fact somehow.

But if after construction the ios_base is in an indeterminate state, and that state is not made determinate before the destructor is called, then how would the destructor know if any callbacks had indeed been registered? And if the number of callbacks that had been registered is indeterminate, then is not the behavior of the destructor undefined?

By comparison, the basic_ios class description in 27.4.4.1 paragraph 2 makes it explicit that destruction before initialization results in undefined behavior.

Proposed resolution:

Modify 27.4.2.7 paragraph 1 from

> Effects: Each ios_base member has an indeterminate value after construction.

to

> Effects: Each ios_base member has an indeterminate value after construction. These members must be initialized by calling basic_ios::init. If an ios_base object is destroyed before these initializations have taken place, the behavior is undefined.

### 221. num_get<>::do_get stage 2 processing broken

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 Submitter: Matt Austern Opened: 2000-03-14 Last modified: 2008-09-26

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Discussion:

Stage 2 processing of numeric conversion is broken.

Table 55 in 22.2.2.1.2 says that when basefield is 0 the integral conversion specifier is %i. A %i specifier determines a number's base by its prefix (0 for octal, 0x for hex), so the intention is clearly that a 0x prefix is allowed. Paragraph 8 in the same section, however, describes very precisely how characters are processed. (It must be done "as if" by a specified code fragment.) That description does not allow a 0x prefix to be recognized.

Very roughly, stage 2 processing reads a char_type ct. It converts ct to a char, not by using narrow but by looking it up in a translation table that was created by widening the string literal "0123456789abcdefABCDEF+-". The character "x" is not found in that table, so it can't be recognized by stage 2 processing.

Proposed resolution:

In 22.2.2.1.2 paragraph 8, replace the line:

>     static const char src[] = "0123456789abcdefABCDEF+-";

with the line:

>     static const char src[] = "0123456789abcdefxABCDEFX+-";

Rationale:

If we're using the technique of widening a string literal, the string literal must contain every character we wish to recognize. This technique has the consequence that alternate representations of digits will not be recognized. This design decision was made deliberately, with full knowledge of that limitation.

### 222. Are throw clauses necessary if a throw is already implied by the effects clause?

Section: 17.5.1.4 [structure.specifications] Status: TC1 Submitter: Judy Ward Opened: 2000-03-17 Last modified: 2008-09-26

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Discussion:

Section 21.3.6.8 describes the basic_string::compare function this way:

>     21.3.6.8 - basic_string::compare [lib.string::compare]

>     int compare(size_type pos1, size_type n1,
>                     const basic_string<charT,traits,Allocator>&  str ,
>                     size_type  pos2 , size_type  n2 ) const;

>     -4- Returns:

>         basic_string<charT,traits,Allocator>(*this,pos1,n1).compare(
>                      basic_string<charT,traits,Allocator>(str,pos2,n2)) .

and the constructor that's implicitly called by the above is defined to throw an out-of-range exception if pos > str.size(). See section 21.4.1 [string.require] paragraph 4.

On the other hand, the compare function descriptions themselves don't have "Throws: " clauses and according to 17.3.1.3, paragraph 3, elements that do not apply to a function are omitted.

So it seems there is an inconsistency in the standard -- are the "Effects" clauses correct, or are the "Throws" clauses missing?

Proposed resolution:

In 17.5.1.4 [structure.specifications] paragraph 3, the footnote 148 attached to the sentence "Descriptions of function semantics contain the following elements (as appropriate):", insert the word "further" so that the foot note reads:

> To save space, items that do not apply to a function are omitted. For example, if a function does not specify any further preconditions, there will be no "Requires" paragraph.

Rationale:

The standard is somewhat inconsistent, but a failure to note a throw condition in a throws clause does not grant permission not to throw. The inconsistent wording is in a footnote, and thus non-normative. The proposed resolution from the LWG clarifies the footnote.

### 223. reverse algorithm should use iter_swap rather than swap

Section: 25.3.10 [alg.reverse] Status: TC1 Submitter: Dave Abrahams Opened: 2000-03-21 Last modified: 2008-09-26

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Discussion:

Shouldn't the effects say "applies iter_swap to all pairs..."?

Proposed resolution:

In 25.3.10 [alg.reverse], replace:

> Effects: For each non-negative integer i <= (last - first)/2, applies swap to all pairs of iterators first + i, (last - i) - 1.

with:

> Effects: For each non-negative integer i <= (last - first)/2, applies iter_swap to all pairs of iterators first + i, (last - i) - 1.

### 224. clear() complexity for associative containers refers to undefined N

Section: 23.2.4 [associative.reqmts] Status: TC1 Submitter: Ed Brey Opened: 2000-03-23 Last modified: 2008-09-26

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Discussion:

In the associative container requirements table in 23.1.2 paragraph 7, a.clear() has complexity "log(size()) + N". However, the meaning of N is not defined.

Proposed resolution:

In the associative container requirements table in 23.1.2 paragraph 7, the complexity of a.clear(), change "log(size()) + N" to "linear in `size()`".

Rationale:

It's the "log(size())", not the "N", that is in error: there's no difference between O(N) and O(N + log(N)). The text in the standard is probably an incorrect cut-and-paste from the range version of `erase`.

### 225. std:: algorithms use of other unqualified algorithms

Section: 17.6.4.4 [global.functions] Status: CD1 Submitter: Dave Abrahams Opened: 2000-04-01 Last modified: 2008-09-26

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Discussion:

Are algorithms in std:: allowed to use other algorithms without qualification, so functions in user namespaces might be found through Koenig lookup?

For example, a popular standard library implementation includes this implementation of std::unique:

>     namespace std {
>         template <class _ForwardIter>
>         _ForwardIter unique(_ForwardIter __first, _ForwardIter __last) {
>           __first = adjacent_find(__first, __last);
>           return unique_copy(__first, __last, __first);
>         }
>         }

Imagine two users on opposite sides of town, each using unique on his own sequences bounded by my_iterators . User1 looks at his standard library implementation and says, "I know how to implement a more efficient unique_copy for my_iterators", and writes:

>     namespace user1 {
>         class my_iterator;
>         // faster version for my_iterator
>         my_iterator unique_copy(my_iterator, my_iterator, my_iterator);
>         }

user1::unique_copy() is selected by Koenig lookup, as he intended.

User2 has other needs, and writes:

>     namespace user2 {
>         class my_iterator;
>         // Returns true iff *c is a unique copy of *a and *b.
>         bool unique_copy(my_iterator a, my_iterator b, my_iterator c);
>         }

User2 is shocked to find later that his fully-qualified use of std::unique(user2::my_iterator, user2::my_iterator, user2::my_iterator) fails to compile (if he's lucky). Looking in the standard, he sees the following Effects clause for unique():

> Effects: Eliminates all but the first element from every consecutive group of equal elements referred to by the iterator i in the range [first, last) for which the following corresponding conditions hold: *i == *(i - 1) or pred(*i, *(i - 1)) != false

The standard gives user2 absolutely no reason to think he can interfere with std::unique by defining names in namespace user2. His standard library has been built with the template export feature, so he is unable to inspect the implementation. User1 eventually compiles his code with another compiler, and his version of unique_copy silently stops being called. Eventually, he realizes that he was depending on an implementation detail of his library and had no right to expect his unique_copy() to be called portably.

On the face of it, and given above scenario, it may seem obvious that the implementation of unique() shown is non-conforming because it uses unique_copy() rather than ::std::unique_copy(). Most standard library implementations, however, seem to disagree with this notion.

[Tokyo: Steve Adamczyk from the core working group indicates that "std::" is sufficient; leading "::" qualification is not required because any namespace qualification is sufficient to suppress Koenig lookup.]

Proposed resolution:

Add a paragraph and a note at the end of 17.6.4.4 [global.functions]:

> Unless otherwise specified, no global or non-member function in the standard library shall use a function from another namespace which is found through argument-dependent name lookup (3.4.2 [basic.lookup.argdep]).

> [Note: the phrase "unless otherwise specified" is intended to allow Koenig lookup in cases like that of ostream_iterators:
> Effects:

> > *out_stream << value;
> > if(delim != 0) *out_stream << delim;
> > return (*this);

> > --end note]

[Tokyo: The LWG agrees that this is a defect in the standard, but is as yet unsure if the proposed resolution is the best solution. Furthermore, the LWG believes that the same problem of unqualified library names applies to wording in the standard itself, and has opened issue 229 accordingly. Any resolution of issue 225 should be coordinated with the resolution of issue 229.]

[Toronto: The LWG is not sure if this is a defect in the standard. Most LWG members believe that an implementation of `std::unique` like the one quoted in this issue is already illegal, since, under certain circumstances, its semantics are not those specified in the standard. The standard's description of `unique` does not say that overloading `adjacent_find` should have any effect.]

[Curaçao: An LWG-subgroup spent an afternoon working on issues 225, 226, and 229. Their conclusion was that the issues should be separated into an LWG portion (Howard's paper, N1387=02-0045), and a EWG portion (Dave will write a proposal). The LWG and EWG had (separate) discussions of this plan the next day. The proposed resolution for this issue is in accordance with Howard's paper.]

Rationale:

It could be argued that this proposed isn't strictly necessary, that the Standard doesn't grant implementors license to write a standard function that behaves differently than specified in the Standard just because of an unrelated user-defined name in some other namespace. However, this is at worst a clarification. It is surely right that algorithsm shouldn't pick up random names, that user-defined names should have no effect unless otherwise specified. Issue 226 deals with the question of when it is appropriate for the standard to explicitly specify otherwise.

### 226. User supplied specializations or overloads of namespace std function templates

Section: 17.6.3.3 [reserved.names] Status: CD1 Submitter: Dave Abrahams Opened: 2000-04-01 Last modified: 2008-09-26

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Discussion:

The issues are:

1. How can a 3rd party library implementor (lib1) write a version of a standard algorithm which is specialized to work with his own class template?

2. How can another library implementor (lib2) write a generic algorithm which will take advantage of the specialized algorithm in lib1?

This appears to be the only viable answer under current language rules:

>     namespace lib1
>     {
>         // arbitrary-precision numbers using T as a basic unit
>         template <class T>
>         class big_num { //...
>         };

>         // defining this in namespace std is illegal (it would be an
>         // overload), so we hope users will rely on Koenig lookup
>         template <class T>
>         void swap(big_int<T>&, big_int<T>&);
>     }

>     #include <algorithm>
>     namespace lib2
>     {
>         template <class T>
>         void generic_sort(T* start, T* end)
>         {
>                 ...
>             // using-declaration required so we can work on built-in types
>             using std::swap;
>             // use Koenig lookup to find specialized algorithm if available
>             swap(*x, *y);
>         }
>     }

This answer has some drawbacks. First of all, it makes writing lib2 difficult and somewhat slippery. The implementor needs to remember to write the using-declaration, or generic_sort will fail to compile when T is a built-in type. The second drawback is that the use of this style in lib2 effectively "reserves" names in any namespace which defines types which may eventually be used with lib2. This may seem innocuous at first when applied to names like swap, but consider more ambiguous names like unique_copy() instead. It is easy to imagine the user wanting to define these names differently in his own namespace. A definition with semantics incompatible with the standard library could cause serious problems (see issue 225).

Why, you may ask, can't we just partially specialize std::swap()? It's because the language doesn't allow for partial specialization of function templates. If you write:

>     namespace std
>     {
>         template <class T>
>         void swap(lib1::big_int<T>&, lib1::big_int<T>&);
>     }

You have just overloaded std::swap, which is illegal under the current language rules. On the other hand, the following full specialization is legal:

>     namespace std
>     {
>         template <>
>         void swap(lib1::other_type&, lib1::other_type&);
>     }

This issue reflects concerns raised by the "Namespace issue with specialized swap" thread on comp.lang.c++.moderated. A similar set of concerns was earlier raised on the boost.org mailing list and the ACCU-general mailing list. Also see library reflector message c++std-lib-7354.

J. C. van Winkel points out (in c++std-lib-9565) another unexpected fact: it's impossible to output a container of std::pair's using copy and an ostream_iterator, as long as both pair-members are built-in or std:: types. That's because a user-defined operator<< for (for example) std::pair<const std::string, int> will not be found: lookup for operator<< will be performed only in namespace std. Opinions differed on whether or not this was a defect, and, if so, whether the defect is that something is wrong with user-defined functionality and std, or whether it's that the standard library does not provide an operator<< for std::pair<>.

Proposed resolution:

Adopt the wording proposed in Howard Hinnant's paper N1523=03-0106, "Proposed Resolution To LWG issues 225, 226, 229".

[Tokyo: Summary, "There is no conforming way to extend std::swap for user defined templates." The LWG agrees that there is a problem. Would like more information before proceeding. This may be a core issue. Core issue 229 has been opened to discuss the core aspects of this problem. It was also noted that submissions regarding this issue have been received from several sources, but too late to be integrated into the issues list. ]

[Post-Tokyo: A paper with several proposed resolutions, J16/00-0029==WG21/N1252, "Shades of namespace std functions " by Alan Griffiths, is in the Post-Tokyo mailing. It should be considered a part of this issue.]

[Toronto: Dave Abrahams and Peter Dimov have proposed a resolution that involves core changes: it would add partial specialization of function template. The Core Working Group is reluctant to add partial specialization of function templates. It is viewed as a large change, CWG believes that proposal presented leaves some syntactic issues unanswered; if the CWG does add partial specialization of function templates, it wishes to develop its own proposal. The LWG continues to believe that there is a serious problem: there is no good way for users to force the library to use user specializations of generic standard library functions, and in certain cases (e.g. transcendental functions called by `valarray` and `complex`) this is important. Koenig lookup isn't adequate, since names within the library must be qualified with `std` (see issue 225), specialization doesn't work (we don't have partial specialization of function templates), and users aren't permitted to add overloads within namespace std. ]

[Copenhagen: Discussed at length, with no consensus. Relevant papers in the pre-Copenhagen mailing: N1289, N1295, N1296. Discussion focused on four options. (1) Relax restrictions on overloads within namespace std. (2) Mandate that the standard library use unqualified calls for `swap` and possibly other functions. (3) Introduce helper class templates for `swap` and possibly other functions. (4) Introduce partial specialization of function templates. Every option had both support and opposition. Straw poll (first number is support, second is strongly opposed): (1) 6, 4; (2) 6, 7; (3) 3, 8; (4) 4, 4.]

[Redmond: Discussed, again no consensus. Herb presented an argument that a user who is defining a type `T` with an associated `swap` should not be expected to put that `swap` in namespace std, either by overloading or by partial specialization. The argument is that `swap` is part of `T`'s interface, and thus should to in the same namespace as `T` and only in that namespace. If we accept this argument, the consequence is that standard library functions should use unqualified call of `swap`. (And which other functions? Any?) A small group (Nathan, Howard, Jeremy, Dave, Matt, Walter, Marc) will try to put together a proposal before the next meeting.]

[Curaçao: An LWG-subgroup spent an afternoon working on issues 225, 226, and 229. Their conclusion was that the issues should be separated into an LWG portion (Howard's paper, N1387=02-0045), and a EWG portion (Dave will write a proposal). The LWG and EWG had (separate) discussions of this plan the next day. The proposed resolution is the one proposed by Howard.]

[Santa Cruz: the LWG agreed with the general direction of Howard's paper, N1387. (Roughly: Koenig lookup is disabled unless we say otherwise; this issue is about when we do say otherwise.) However, there were concerns about wording. Howard will provide new wording. Bill and Jeremy will review it.]

[Kona: Howard proposed the new wording. The LWG accepted his proposed resolution.]

Rationale:

Informally: introduce a Swappable concept, and specify that the value types of the iterators passed to certain standard algorithms (such as iter_swap, swap_ranges, reverse, rotate, and sort) conform to that concept. The Swappable concept will make it clear that these algorithms use unqualified lookup for the calls to `swap`. Also, in 26.6.3.3 [valarray.transcend] paragraph 1, state that the valarray transcendentals use unqualified lookup.

### 227. std::swap() should require CopyConstructible or DefaultConstructible arguments

Section: 25.3.3 [alg.swap] Status: TC1 Submitter: Dave Abrahams Opened: 2000-04-09 Last modified: 2008-09-26

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Discussion:

25.2.2 reads:

> `template<class T> void swap(T& a, T& b);`
> Requires: Type T is Assignable (_lib.container.requirements_).
> Effects: Exchanges values stored in two locations.

The only reasonable** generic implementation of swap requires construction of a new temporary copy of one of its arguments:

>     template<class T> void swap(T& a, T& b);
>       {
>           T tmp(a);
>           a = b;
>           b = tmp;
>       }

But a type which is only Assignable cannot be swapped by this implementation.

**Yes, there's also an unreasonable implementation which would require T to be DefaultConstructible instead of CopyConstructible. I don't think this is worthy of consideration:

>     template<class T> void swap(T& a, T& b);
>     {
>         T tmp;
>         tmp = a;
>         a = b;
>         b = tmp;
>     }

Proposed resolution:

Change 25.2.2 paragraph 1 from:

> Requires: Type T is Assignable (23.1).

to:

> Requires: Type T is CopyConstructible (20.1.3) and Assignable (23.1)

### 228. Incorrect specification of "..._byname" facets

Section: 22.4 [locale.categories] Status: CD1 Submitter: Dietmar Kühl Opened: 2000-04-20 Last modified: 2008-09-26

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Discussion:

The sections 22.4.1.2 [locale.ctype.byname], 22.4.1.5 [locale.codecvt.byname], sref ref="22.2.1.6", 22.4.3.2 [locale.numpunct.byname], 22.4.4.2 [locale.collate.byname], 22.4.5.4 [locale.time.put.byname], 22.4.6.4 [locale.moneypunct.byname], and 22.4.7.2 [locale.messages.byname] overspecify the definitions of the "..._byname" classes by listing a bunch of virtual functions. At the same time, no semantics of these functions are defined. Real implementations do not define these functions because the functional part of the facets is actually implemented in the corresponding base classes and the constructor of the "..._byname" version just provides suitable date used by these implementations. For example, the 'numpunct' methods just return values from a struct. The base class uses a statically initialized struct while the derived version reads the contents of this struct from a table. However, no virtual function is defined in 'numpunct_byname'.

For most classes this does not impose a problem but specifically for 'ctype' it does: The specialization for 'ctype_byname<char>' is required because otherwise the semantics would change due to the virtual functions defined in the general version for 'ctype_byname': In 'ctype<char>' the method 'do_is()' is not virtual but it is made virtual in both 'ctype<cT>' and 'ctype_byname<cT>'. Thus, a class derived from 'ctype_byname<char>' can tell whether this class is specialized or not under the current specification: Without the specialization, 'do_is()' is virtual while with specialization it is not virtual.

Proposed resolution:

Change section 22.2.1.2 (lib.locale.ctype.byname) to become:

         namespace std {
           template <class charT>
           class ctype_byname : public ctype<charT> {
           public:
             typedef ctype<charT>::mask mask;
             explicit ctype_byname(const char*, size_t refs = 0);
           protected:
            ~ctype_byname();             //  virtual
           };
         }

Change section 22.2.1.6 (lib.locale.codecvt.byname) to become:

        namespace std {
          template <class internT, class externT, class stateT>
          class codecvt_byname : public codecvt<internT, externT, stateT> {
          public:
           explicit codecvt_byname(const char*, size_t refs = 0);
          protected:
          ~codecvt_byname();             //  virtual
           };
         }

Change section 22.2.3.2 (lib.locale.numpunct.byname) to become:

         namespace std {
           template <class charT>
           class numpunct_byname : public numpunct<charT> {
         //  this class is specialized for  char  and  wchar_t.
           public:
             typedef charT                char_type;
             typedef basic_string<charT>  string_type;
             explicit numpunct_byname(const char*, size_t refs = 0);
           protected:
            ~numpunct_byname();          //  virtual
           };
         }

Change section 22.2.4.2 (lib.locale.collate.byname) to become:

         namespace std {
           template <class charT>
           class collate_byname : public collate<charT> {
           public:
             typedef basic_string<charT> string_type;
             explicit collate_byname(const char*, size_t refs = 0);
           protected:
            ~collate_byname();           //  virtual
           };
         }

Change section 22.2.5.2 (lib.locale.time.get.byname) to become:

         namespace std {
           template <class charT, class InputIterator = istreambuf_iterator<charT> >
           class time_get_byname : public time_get<charT, InputIterator> {
           public:
             typedef time_base::dateorder dateorder;
             typedef InputIterator        iter_type

             explicit time_get_byname(const char*, size_t refs = 0);
           protected:
            ~time_get_byname();          //  virtual
           };
         }

Change section 22.2.5.4 (lib.locale.time.put.byname) to become:

         namespace std {
           template <class charT, class OutputIterator = ostreambuf_iterator<charT> >
           class time_put_byname : public time_put<charT, OutputIterator>
           {
           public:
             typedef charT          char_type;
             typedef OutputIterator iter_type;

             explicit time_put_byname(const char*, size_t refs = 0);
           protected:
            ~time_put_byname();          //  virtual
           };
         }"

Change section 22.2.6.4 (lib.locale.moneypunct.byname) to become:

         namespace std {
           template <class charT, bool Intl = false>
           class moneypunct_byname : public moneypunct<charT, Intl> {
           public:
             typedef money_base::pattern pattern;
             typedef basic_string<charT> string_type;

             explicit moneypunct_byname(const char*, size_t refs = 0);
           protected:
            ~moneypunct_byname();        //  virtual
           };
         }

Change section 22.2.7.2 (lib.locale.messages.byname) to become:

         namespace std {
           template <class charT>
           class messages_byname : public messages<charT> {
           public:
             typedef messages_base::catalog catalog;
             typedef basic_string<charT>    string_type;

             explicit messages_byname(const char*, size_t refs = 0);
           protected:
            ~messages_byname();          //  virtual
           };
         }

Remove section 22.4.1.4 [locale.codecvt] completely (because in this case only those members are defined to be virtual which are defined to be virtual in 'ctype<cT>'.)

[Post-Tokyo: Dietmar Kühl submitted this issue at the request of the LWG to solve the underlying problems raised by issue 138.]

[Copenhagen: proposed resolution was revised slightly, to remove three last virtual functions from `messages_byname`.]

### 229. Unqualified references of other library entities

Section: 17.6.1.1 [contents] Status: CD1 Submitter: Steve Clamage Opened: 2000-04-19 Last modified: 2008-09-26

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Discussion:

Throughout the library chapters, the descriptions of library entities refer to other library entities without necessarily qualifying the names.

For example, section 25.2.2 "Swap" describes the effect of swap_ranges in terms of the unqualified name "swap". This section could reasonably be interpreted to mean that the library must be implemented so as to do a lookup of the unqualified name "swap", allowing users to override any ::std::swap function when Koenig lookup applies.

Although it would have been best to use explicit qualification with "::std::" throughout, too many lines in the standard would have to be adjusted to make that change in a Technical Corrigendum.

Issue 182, which addresses qualification of `size_t`, is a special case of this.

Proposed resolution:

To section 17.4.1.1 "Library contents" Add the following paragraph:

> Whenever a name x defined in the standard library is mentioned, the name x is assumed to be fully qualified as ::std::x, unless explicitly described otherwise. For example, if the Effects section for library function F is described as calling library function G, the function ::std::G is meant.

[Post-Tokyo: Steve Clamage submitted this issue at the request of the LWG to solve a problem in the standard itself similar to the problem within implementations of library identified by issue 225. Any resolution of issue 225 should be coordinated with the resolution of this issue.]

[post-Toronto: Howard is undecided about whether it is appropriate for all standard library function names referred to in other standard library functions to be explicitly qualified by `std`: it is common advice that users should define global functions that operate on their class in the same namespace as the class, and this requires argument-dependent lookup if those functions are intended to be called by library code. Several LWG members are concerned that valarray appears to require argument-dependent lookup, but that the wording may not be clear enough to fall under "unless explicitly described otherwise".]

[Curaçao: An LWG-subgroup spent an afternoon working on issues 225, 226, and 229. Their conclusion was that the issues should be separated into an LWG portion (Howard's paper, N1387=02-0045), and a EWG portion (Dave will write a proposal). The LWG and EWG had (separate) discussions of this plan the next day. This paper resolves issues 225 and 226. In light of that resolution, the proposed resolution for the current issue makes sense.]

### 230. Assignable specified without also specifying CopyConstructible

Section: 17 [library] Status: CD1 Submitter: Beman Dawes Opened: 2000-04-26 Last modified: 2008-09-26

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Discussion:

Issue 227 identified an instance (std::swap) where Assignable was specified without also specifying CopyConstructible. The LWG asked that the standard be searched to determine if the same defect existed elsewhere.

There are a number of places (see proposed resolution below) where Assignable is specified without also specifying CopyConstructible. There are also several cases where both are specified. For example, X [rand.req].

Proposed resolution:

In 23.2 [container.requirements] table 65 for value_type: change "T is Assignable" to "T is CopyConstructible and Assignable"

In 23.2.4 [associative.reqmts] table 69 X::key_type; change "Key is Assignable" to "Key is CopyConstructible and Assignable"

In 24.2.2 [output.iterators] paragraph 1, change:

> A class or a built-in type X satisfies the requirements of an output iterator if X is an Assignable type (23.1) and also the following expressions are valid, as shown in Table 73:

to:

> A class or a built-in type X satisfies the requirements of an output iterator if X is a CopyConstructible (20.1.3) and Assignable type (23.1) and also the following expressions are valid, as shown in Table 73:

[Post-Tokyo: Beman Dawes submitted this issue at the request of the LWG. He asks that the 25.3.5 [alg.replace] and 25.3.6 [alg.fill] changes be studied carefully, as it is not clear that CopyConstructible is really a requirement and may be overspecification.]

[Portions of the resolution for issue 230 have been superceded by the resolution of issue 276.]

Rationale:

The original proposed resolution also included changes to input iterator, fill, and replace. The LWG believes that those changes are not necessary. The LWG considered some blanket statement, where an Assignable type was also required to be Copy Constructible, but decided against this because fill and replace really don't require the Copy Constructible property.

### 231. Precision in iostream?

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: CD1 Submitter: James Kanze, Stephen Clamage Opened: 2000-04-25 Last modified: 2008-09-26

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Discussion:

What is the following program supposed to output?

    #include <iostream>

        int
        main()
        {
            std::cout.setf( std::ios::scientific , std::ios::floatfield ) ;
            std::cout.precision( 0 ) ;
            std::cout << 1.00 << '\n' ;
            return 0 ;
        }

From my C experience, I would expect "1e+00"; this is what `printf("%.0e" , 1.00 );` does. G++ outputs "1.000000e+00".

The only indication I can find in the standard is 22.2.2.2.2/11, where it says "For conversion from a floating-point type, if (flags & fixed) != 0 or if str.precision() > 0, then str.precision() is specified in the conversion specification." This is an obvious error, however, fixed is not a mask for a field, but a value that a multi-bit field may take -- the results of and'ing fmtflags with ios::fixed are not defined, at least not if ios::scientific has been set. G++'s behavior corresponds to what might happen if you do use (flags & fixed) != 0 with a typical implementation (floatfield == 3 << something, fixed == 1 << something, and scientific == 2 << something).

Presumably, the intent is either (flags & floatfield) != 0, or (flags & floatfield) == fixed; the first gives something more or less like the effect of precision in a printf floating point conversion. Only more or less, of course. In order to implement printf formatting correctly, you must know whether the precision was explicitly set or not. Say by initializing it to -1, instead of 6, and stating that for floating point conversions, if precision < -1, 6 will be used, for fixed point, if precision < -1, 1 will be used, etc. Plus, of course, if precision == 0 and flags & floatfield == 0, 1 should be = used. But it probably isn't necessary to emulate all of the anomalies of printf:-).

Proposed resolution:

Replace 22.4.2.2.2 [facet.num.put.virtuals], paragraph 11, with the following sentence:

> For conversion from a floating-point type, `str.precision()` is specified in the conversion specification.

Rationale:

The floatfield determines whether numbers are formatted as if with %f, %e, or %g. If the `fixed` bit is set, it's %f, if `scientific` it's %e, and if both bits are set, or neither, it's %g.

Turning to the C standard, a precision of 0 is meaningful for %f and %e. For %g, precision 0 is taken to be the same as precision 1.

The proposed resolution has the effect that if neither `fixed` nor `scientific` is set we'll be specifying a precision of 0, which will be internally turned into 1. There's no need to call it out as a special case.

The output of the above program will be "1e+00".

[Post-Curaçao: Howard provided improved wording covering the case where precision is 0 and mode is %g.]

### 232. "depends" poorly defined in 17.4.3.1

Section: 17.6.3.3 [reserved.names] Status: CD1 Submitter: Peter Dimov Opened: 2000-04-18 Last modified: 2008-09-26

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Discussion:

17.4.3.1/1 uses the term "depends" to limit the set of allowed specializations of standard templates to those that "depend on a user-defined name of external linkage."

This term, however, is not adequately defined, making it possible to construct a specialization that is, I believe, technically legal according to 17.4.3.1/1, but that specializes a standard template for a built-in type such as 'int'.

The following code demonstrates the problem:

>     #include <algorithm>

>     template<class T> struct X
>     {
>      typedef T type;
>     };

>     namespace std
>     {
>      template<> void swap(::X<int>::type& i, ::X<int>::type& j);
>     }

Proposed resolution:

Change "user-defined name" to "user-defined type".

Rationale:

This terminology is used in section 2.5.2 and 4.1.1 of The C++ Programming Language. It disallows the example in the issue, since the underlying type itself is not user-defined. The only possible problem I can see is for non-type templates, but there's no possible way for a user to come up with a specialization for bitset, for example, that might not have already been specialized by the implementor?

[Toronto: this may be related to issue 120.]

[post-Toronto: Judy provided the above proposed resolution and rationale.]

### 233. Insertion hints in associative containers

Section: 23.2.4 [associative.reqmts] Status: CD1 Submitter: Andrew Koenig Opened: 2000-04-30 Last modified: 2008-09-26

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Duplicate of: 192, 246

Discussion:

If `mm` is a multimap and `p` is an iterator into the multimap, then `mm.insert(p, x)` inserts `x` into `mm` with `p` as a hint as to where it should go. Table 69 claims that the execution time is amortized constant if the insert winds up taking place adjacent to `p`, but does not say when, if ever, this is guaranteed to happen. All it says it that `p` is a hint as to where to insert.

The question is whether there is any guarantee about the relationship between `p` and the insertion point, and, if so, what it is.

I believe the present state is that there is no guarantee: The user can supply `p`, and the implementation is allowed to disregard it entirely.

Additional comments from Nathan:
The vote [in Redmond] was on whether to elaborately specify the use of the hint, or to require behavior only if the value could be inserted adjacent to the hint. I would like to ensure that we have a chance to vote for a deterministic treatment: "before, if possible, otherwise after, otherwise anywhere appropriate", as an alternative to the proposed "before or after, if possible, otherwise [...]".

[Toronto: there was general agreement that this is a real defect: when inserting an element x into a multiset that already contains several copies of x, there is no way to know whether the hint will be used. The proposed resolution was that the new element should always be inserted as close to the hint as possible. So, for example, if there is a subsequence of equivalent values, then providing a.begin() as the hint means that the new element should be inserted before the subsequence even if a.begin() is far away. JC van Winkel supplied precise wording for this proposed resolution, and also for an alternative resolution in which hints are only used when they are adjacent to the insertion point.]

[Copenhagen: the LWG agreed to the original proposed resolution, in which an insertion hint would be used even when it is far from the insertion point. This was contingent on seeing a example implementation showing that it is possible to implement this requirement without loss of efficiency. John Potter provided such a example implementation.]

[Redmond: The LWG was reluctant to adopt the proposal that emerged from Copenhagen: it seemed excessively complicated, and went beyond fixing the defect that we identified in Toronto. PJP provided the new wording described in this issue. Nathan agrees that we shouldn't adopt the more detailed semantics, and notes: "we know that you can do it efficiently enough with a red-black tree, but there are other (perhaps better) balanced tree techniques that might differ enough to make the detailed semantics hard to satisfy."]

[Curaçao: Nathan should give us the alternative wording he suggests so the LWG can decide between the two options.]

[Lillehammer: The LWG previously rejected the more detailed semantics, because it seemed more loike a new feature than like defect fixing. We're now more sympathetic to it, but we (especially Bill) are still worried about performance. N1780 describes a naive algorithm, but it's not clear whether there is a non-naive implementation. Is it possible to implement this as efficently as the current version of insert?]

[Post Lillehammer: N1780 updated in post meeting mailing with feedback from Lillehammer with more information regarding performance. ]

[ Batavia: 1780 accepted with minor wording changes in the proposed wording (reflected in the proposed resolution below). Concerns about the performance of the algorithm were satisfactorily met by 1780. 371 already handles the stability of equal ranges and so that part of the resolution from 1780 is no longer needed (or reflected in the proposed wording below). ]

Proposed resolution:

Change the indicated rows of the "Associative container requirements" Table in 23.2.4 [associative.reqmts] to:

Associative container requirements
expression | return type | assertion/note pre/post-condition | complexity
--- | --- | --- | ---
`a_eq.insert(t)` | `iterator` | inserts `t` and returns the iterator pointing to the newly inserted element. If a range containing elements equivalent to `t` exists in `a_eq`, `t` is inserted at the end of that range. | logarithmic
`a.insert(p,t)` | `iterator` | inserts `t` if and only if there is no element with key equivalent to the key of `t` in containers with unique keys; always inserts `t` in containers with equivalent keys. always returns the iterator pointing to the element with key equivalent to the key of `t`. iterator `p` is a hint pointing to where the insert should start to search. `t` is inserted as close as possible to the position just prior to `p`. | logarithmic in general, but amortized constant if `t` is inserted right after before `p`.

### 234. Typos in allocator definition

Section: 20.8.8.1 [allocator.members] Status: CD1 Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2008-09-26

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Discussion:

In paragraphs 12 and 13 the effects of `construct()` and `destruct()` are described as returns but the functions actually return `void`.

Proposed resolution:

Substitute "Returns" by "Effect".

### 235. No specification of default ctor for reverse_iterator

Section: 24.5.1.1 [reverse.iterator] Status: CD1 Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2008-09-26

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Discussion:

The declaration of `reverse_iterator` lists a default constructor. However, no specification is given what this constructor should do.

Proposed resolution:

In section 24.5.1.3.1 [reverse.iter.cons] add the following paragraph:

> `reverse_iterator()`

> Default initializes `current`. Iterator operations applied to the resulting iterator have defined behavior if and only if the corresponding operations are defined on a default constructed iterator of type `Iterator`.

[pre-Copenhagen: Dietmar provide wording for proposed resolution.]

### 237. Undefined expression in complexity specification

Section: 23.3.2.1 [deque.cons] Status: CD1 Submitter: Dietmar Kühl Opened: 2000-04-24 Last modified: 2008-09-26

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Discussion:

The complexity specification in paragraph 6 says that the complexity is linear in `first - last`. Even if `operator-()` is defined on iterators this term is in general undefined because it would have to be `last - first`.

Proposed resolution:

Change paragraph 6 from

> Linear in first - last.

to become

> Linear in distance(first, last).

### 238. Contradictory results of stringbuf initialization.

Section: 27.8.1.1 [stringbuf.cons] Status: CD1 Submitter: Dietmar Kühl Opened: 2000-05-11 Last modified: 2008-09-26

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Discussion:

In 27.7.1.1 paragraph 4 the results of calling the constructor of 'basic_stringbuf' are said to be `str() == str`. This is fine that far but consider this code:

      std::basic_stringbuf<char> sbuf("hello, world", std::ios_base::openmode(0));
      std::cout << "'" << sbuf.str() << "'\n";

Paragraph 3 of 27.7.1.1 basically says that in this case neither the output sequence nor the input sequence is initialized and paragraph 2 of 27.7.1.2 basically says that `str()` either returns the input or the output sequence. None of them is initialized, ie. both are empty, in which case the return from `str()` is defined to be `basic_string<cT>()`.

However, probably only test cases in some testsuites will detect this "problem"...

Proposed resolution:

Remove 27.7.1.1 paragraph 4.

Rationale:

We could fix 27.7.1.1 paragraph 4, but there would be no point. If we fixed it, it would say just the same thing as text that's already in the standard.

### 239. Complexity of unique() and/or unique_copy incorrect

Section: 25.3.9 [alg.unique] Status: CD1 Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2008-09-26

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Discussion:

The complexity of unique and unique_copy are inconsistent with each other and inconsistent with the implementations. The standard specifies:

for unique():

> -3- Complexity: If the range (last - first) is not empty, exactly (last - first) - 1 applications of the corresponding predicate, otherwise no applications of the predicate.

for unique_copy():

> -7- Complexity: Exactly last - first applications of the corresponding predicate.

The implementations do it the other way round: unique() applies the predicate last-first times and unique_copy() applies it last-first-1 times.

As both algorithms use the predicate for pair-wise comparison of sequence elements I don't see a justification for unique_copy() applying the predicate last-first times, especially since it is not specified to which pair in the sequence the predicate is applied twice.

Proposed resolution:

Change both complexity sections in 25.3.9 [alg.unique] to:

> Complexity: For nonempty ranges, exactly last - first - 1 applications of the corresponding predicate.

### 240. Complexity of adjacent_find() is meaningless

Section: 25.2.8 [alg.adjacent.find] Status: CD1 Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2008-09-26

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Discussion:

The complexity section of adjacent_find is defective:

>     template <class ForwardIterator>
>     ForwardIterator adjacent_find(ForwardIterator first, ForwardIterator last
>                                   BinaryPredicate pred);

> -1- Returns: The first iterator i such that both i and i + 1 are in the range [first, last) for which the following corresponding conditions hold: *i == *(i + 1), pred(*i, *(i + 1)) != false. Returns last if no such iterator is found.

> -2- Complexity: Exactly find(first, last, value) - first applications of the corresponding predicate.

In the Complexity section, it is not defined what "value" is supposed to mean. My best guess is that "value" means an object for which one of the conditions pred(*i,value) or pred(value,*i) is true, where i is the iterator defined in the Returns section. However, the value type of the input sequence need not be equality-comparable and for this reason the term find(first, last, value) - first is meaningless.

A term such as find_if(first, last, bind2nd(pred,*i)) - first or find_if(first, last, bind1st(pred,*i)) - first might come closer to the intended specification. Binders can only be applied to function objects that have the function call operator declared const, which is not required of predicates because they can have non-const data members. For this reason, a specification using a binder could only be an "as-if" specification.

Proposed resolution:

Change the complexity section in 25.2.8 [alg.adjacent.find] to:

> For a nonempty range, exactly `min((i - first) + 1, (last - first) - 1)` applications of the corresponding predicate, where i is `adjacent_find`'s return value.

[Copenhagen: the original resolution specified an upper bound. The LWG preferred an exact count.]

### 241. Does unique_copy() require CopyConstructible and Assignable?

Section: 25.3.9 [alg.unique] Status: CD1 Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2008-09-26

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Discussion:

Some popular implementations of unique_copy() create temporary copies of values in the input sequence, at least if the input iterator is a pointer. Such an implementation is built on the assumption that the value type is CopyConstructible and Assignable.

It is common practice in the standard that algorithms explicitly specify any additional requirements that they impose on any of the types used by the algorithm. An example of an algorithm that creates temporary copies and correctly specifies the additional requirements is accumulate(), X [rand.req].

Since the specifications of unique() and unique_copy() do not require CopyConstructible and Assignable of the InputIterator's value type the above mentioned implementations are not standard-compliant. I cannot judge whether this is a defect in the standard or a defect in the implementations.

Proposed resolution:

In 25.2.8 change:

> -4- Requires: The ranges [first, last) and [result, result+(last-first)) shall not overlap.

to:

> -4- Requires: The ranges [first, last) and [result, result+(last-first)) shall not overlap. The expression *result = *first must be valid. If neither InputIterator nor OutputIterator meets the requirements of forward iterator then the value type of InputIterator must be copy constructible. Otherwise copy constructible is not required.

[Redmond: the original proposed resolution didn't impose an explicit requirement that the iterator's value type must be copy constructible, on the grounds that an input iterator's value type must always be copy constructible. Not everyone in the LWG thought that this requirement was clear from table 72. It has been suggested that it might be possible to implement `unique_copy` without requiring assignability, although current implementations do impose that requirement. Howard provided new wording.]

[ Curaçao: The LWG changed the PR editorially to specify "neither...nor...meet..." as clearer than "both...and...do not meet...". Change believed to be so minor as not to require re-review. ]

### 242. Side effects of function objects

Section: 25.3.4 [alg.transform], 26.5 [rand] Status: CD1 Submitter: Angelika Langer Opened: 2000-05-15 Last modified: 2008-09-26

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Discussion:

The algorithms transform(), accumulate(), inner_product(), partial_sum(), and adjacent_difference() require that the function object supplied to them shall not have any side effects.

The standard defines a side effect in 1.9 [intro.execution] as:

> -7- Accessing an object designated by a volatile lvalue (basic.lval), modifying an object, calling a library I/O function, or calling a function that does any of those operations are all side effects, which are changes in the state of the execution environment.

As a consequence, the function call operator of a function object supplied to any of the algorithms listed above cannot modify data members, cannot invoke any function that has a side effect, and cannot even create and modify temporary objects. It is difficult to imagine a function object that is still useful under these severe limitations. For instance, any non-trivial transformator supplied to transform() might involve creation and modification of temporaries, which is prohibited according to the current wording of the standard.

On the other hand, popular implementations of these algorithms exhibit uniform and predictable behavior when invoked with a side-effect-producing function objects. It looks like the strong requirement is not needed for efficient implementation of these algorithms.

The requirement of side-effect-free function objects could be replaced by a more relaxed basic requirement (which would hold for all function objects supplied to any algorithm in the standard library):

> A function objects supplied to an algorithm shall not invalidate any iterator or sequence that is used by the algorithm. Invalidation of the sequence includes destruction of the sorting order if the algorithm relies on the sorting order (see section 25.3 - Sorting and related operations [lib.alg.sorting]).

I can't judge whether it is intended that the function objects supplied to transform(), accumulate(), inner_product(), partial_sum(), or adjacent_difference() shall not modify sequence elements through dereferenced iterators.

It is debatable whether this issue is a defect or a change request. Since the consequences for user-supplied function objects are drastic and limit the usefulness of the algorithms significantly I would consider it a defect.

Proposed resolution:

Things to notice about these changes:

1. The fully-closed ("[]" as opposed to half-closed "[)" ranges are intentional. we want to prevent side-effects from invalidating the end iterators.
2. That has the unintentional side-effect of prohibiting modification of the end element as a side-effect. This could conceivably be significant in some cases.
3. The wording also prevents side-effects from modifying elements of the output sequence. I can't imagine why anyone would want to do this, but it is arguably a restriction that implementors don't need to place on users.
4. Lifting the restrictions imposed in #2 and #3 above is possible and simple, but would require more verbiage.

Change 25.2.3/2 from:

> -2- Requires: op and binary_op shall not have any side effects.

to:

> -2- Requires: in the ranges [first1, last1], [first2, first2 + (last1 - first1)] and [result, result + (last1- first1)], op and binary_op shall neither modify elements nor invalidate iterators or subranges. [Footnote: The use of fully closed ranges is intentional --end footnote]

Change 25.2.3/2 from:

> -2- Requires: op and binary_op shall not have any side effects.

to:

> -2- Requires: op and binary_op shall not invalidate iterators or subranges, or modify elements in the ranges [first1, last1], [first2, first2 + (last1 - first1)], and [result, result + (last1 - first1)]. [Footnote: The use of fully closed ranges is intentional --end footnote]

Change 26.4.1/2 from:

> -2- Requires: T must meet the requirements of CopyConstructible (lib.copyconstructible) and Assignable (lib.container.requirements) types. binary_op shall not cause side effects.

to:

> -2- Requires: T must meet the requirements of CopyConstructible (lib.copyconstructible) and Assignable (lib.container.requirements) types. In the range [first, last], binary_op shall neither modify elements nor invalidate iterators or subranges. [Footnote: The use of a fully closed range is intentional --end footnote]

Change 26.4.2/2 from:

> -2- Requires: T must meet the requirements of CopyConstructible (lib.copyconstructible) and Assignable (lib.container.requirements) types. binary_op1 and binary_op2 shall not cause side effects.

to:

> -2- Requires: T must meet the requirements of CopyConstructible (lib.copyconstructible) and Assignable (lib.container.requirements) types. In the ranges [first, last] and [first2, first2 + (last - first)], binary_op1 and binary_op2 shall neither modify elements nor invalidate iterators or subranges. [Footnote: The use of fully closed ranges is intentional --end footnote]

Change 26.4.3/4 from:

> -4- Requires: binary_op is expected not to have any side effects.

to:

> -4- Requires: In the ranges [first, last] and [result, result + (last - first)], binary_op shall neither modify elements nor invalidate iterators or subranges. [Footnote: The use of fully closed ranges is intentional --end footnote]

Change 26.4.4/2 from:

> -2- Requires: binary_op shall not have any side effects.

to:

> -2- Requires: In the ranges [first, last] and [result, result + (last - first)], binary_op shall neither modify elements nor invalidate iterators or subranges. [Footnote: The use of fully closed ranges is intentional --end footnote]

[Toronto: Dave Abrahams supplied wording.]

[Copenhagen: Proposed resolution was modified slightly. Matt added footnotes pointing out that the use of closed ranges was intentional.]

### 243. `get` and `getline` when sentry reports failure

Section: 27.7.1.3 [istream.unformatted] Status: CD1 Submitter: Martin Sebor Opened: 2000-05-15 Last modified: 2008-09-26

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Discussion:

basic_istream<>::get(), and basic_istream<>::getline(), are unclear with respect to the behavior and side-effects of the named functions in case of an error.

27.6.1.3, p1 states that "... If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input..." It is not clear from this (or the rest of the paragraph) what precisely the behavior should be when the sentry ctor exits by throwing an exception or when the sentry object returns false. In particular, what is the number of characters extracted that gcount() returns supposed to be?

27.6.1.3 p8 and p19 say about the effects of get() and getline(): "... In any case, it then stores a null character (using charT()) into the next successive location of the array." Is not clear whether this sentence applies if either of the conditions above holds (i.e., when sentry fails).

Proposed resolution:

Add to 27.6.1.3, p1 after the sentence

> "... If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input."

the following

> "Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object returns false, when converted to a value of type bool, the function returns without attempting to obtain any input. In either case the number of extracted characters is set to 0; unformatted input functions taking a character array of non-zero size as an argument shall also store a null character (using charT()) in the first location of the array."

Rationale:

Although the general philosophy of the input functions is that the argument should not be modified upon failure, `getline` historically added a terminating null unconditionally. Most implementations still do that. Earlier versions of the draft standard had language that made this an unambiguous requirement; those words were moved to a place where their context made them less clear. See Jerry Schwarz's message c++std-lib-7618.

### 247. `vector`, `deque::insert` complexity

Section: 23.3.6.4 [vector.modifiers] Status: CD1 Submitter: Lisa Lippincott Opened: 2000-06-06 Last modified: 2008-09-26

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Discussion:

Paragraph 2 of 23.3.6.4 [vector.modifiers] describes the complexity of `vector::insert`:

> Complexity: If first and last are forward iterators, bidirectional iterators, or random access iterators, the complexity is linear in the number of elements in the range [first, last) plus the distance to the end of the vector. If they are input iterators, the complexity is proportional to the number of elements in the range [first, last) times the distance to the end of the vector.

First, this fails to address the non-iterator forms of `insert`.

Second, the complexity for input iterators misses an edge case -- it requires that an arbitrary number of elements can be added at the end of a `vector` in constant time.

I looked to see if `deque` had a similar problem, and was surprised to find that `deque` places no requirement on the complexity of inserting multiple elements (23.3.2.3 [deque.modifiers], paragraph 3):

> Complexity: In the worst case, inserting a single element into a deque takes time linear in the minimum of the distance from the insertion point to the beginning of the deque and the distance from the insertion point to the end of the deque. Inserting a single element either at the beginning or end of a deque always takes constant time and causes a single call to the copy constructor of T.

Proposed resolution:

Change Paragraph 2 of 23.3.6.4 [vector.modifiers] to

> Complexity: The complexity is linear in the number of elements inserted plus the distance to the end of the vector.

[For input iterators, one may achieve this complexity by first inserting at the end of the `vector`, and then using `rotate`.]

Change 23.3.2.3 [deque.modifiers], paragraph 3, to:

> Complexity: The complexity is linear in the number of elements inserted plus the shorter of the distances to the beginning and end of the deque. Inserting a single element at either the beginning or the end of a deque causes a single call to the copy constructor of T.

Rationale:

This is a real defect, and proposed resolution fixes it: some complexities aren't specified that should be. This proposed resolution does constrain deque implementations (it rules out the most naive possible implementations), but the LWG doesn't see a reason to permit that implementation.

### 248. time_get fails to set eofbit

Section: 22.4.5 [category.time] Status: CD1 Submitter: Martin Sebor Opened: 2000-06-22 Last modified: 2008-09-26

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Discussion:

There is no requirement that any of time_get member functions set ios::eofbit when they reach the end iterator while parsing their input. Since members of both the num_get and money_get facets are required to do so (22.2.2.1.2, and 22.2.6.1.2, respectively), time_get members should follow the same requirement for consistency.

Proposed resolution:

Add paragraph 2 to section 22.2.5.1 with the following text:

> If the end iterator is reached during parsing by any of the get() member functions, the member sets ios_base::eofbit in err.

Rationale:

Two alternative resolutions were proposed. The LWG chose this one because it was more consistent with the way eof is described for other input facets.

### 250. splicing invalidates iterators

Section: 23.3.4.4 [list.ops] Status: CD1 Submitter: Brian Parker Opened: 2000-07-14 Last modified: 2008-09-26

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Discussion:

Section 23.3.4.4 [list.ops] states that

      void splice(iterator position, list<T, Allocator>& x);

invalidates all iterators and references to list `x`.

This is unnecessary and defeats an important feature of splice. In fact, the SGI STL guarantees that iterators to `x` remain valid after `splice`.

Proposed resolution:

Add a footnote to 23.3.4.4 [list.ops], paragraph 1:

> [Footnote: As specified in [default.con.req], paragraphs 4-5, the semantics described in this clause applies only to the case where allocators compare equal. --end footnote]

In 23.3.4.4 [list.ops], replace paragraph 4 with:

> Effects: Inserts the contents of x before position and x becomes empty. Pointers and references to the moved elements of x now refer to those same elements but as members of *this. Iterators referring to the moved elements will continue to refer to their elements, but they now behave as iterators into *this, not into x.

In 23.3.4.4 [list.ops], replace paragraph 7 with:

> Effects: Inserts an element pointed to by i from list x before position and removes the element from x. The result is unchanged if position == i or position == ++i. Pointers and references to *i continue to refer to this same element but as a member of *this. Iterators to *i (including i itself) continue to refer to the same element, but now behave as iterators into *this, not into x.

In 23.3.4.4 [list.ops], replace paragraph 12 with:

> Requires: [first, last) is a valid range in x. The result is undefined if position is an iterator in the range [first, last). Pointers and references to the moved elements of x now refer to those same elements but as members of *this. Iterators referring to the moved elements will continue to refer to their elements, but they now behave as iterators into *this, not into x.

[pre-Copenhagen: Howard provided wording.]

Rationale:

The original proposed resolution said that iterators and references would remain "valid". The new proposed resolution clarifies what that means. Note that this only applies to the case of equal allocators. From [default.con.req] paragraph 4, the behavior of list when allocators compare nonequal is outside the scope of the standard.

### 251. basic_stringbuf missing allocator_type

Section: 27.8.1 [stringbuf] Status: CD1 Submitter: Martin Sebor Opened: 2000-07-28 Last modified: 2008-09-26

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Discussion:

The synopsis for the template class `basic_stringbuf` doesn't list a typedef for the template parameter `Allocator`. This makes it impossible to determine the type of the allocator at compile time. It's also inconsistent with all other template classes in the library that do provide a typedef for the `Allocator` parameter.

Proposed resolution:

Add to the synopses of the class templates basic_stringbuf (27.7.1), basic_istringstream (27.7.2), basic_ostringstream (27.7.3), and basic_stringstream (27.7.4) the typedef:

      typedef Allocator allocator_type;

### 252. missing casts/C-style casts used in iostreams

Section: 27.8 [string.streams] Status: CD1 Submitter: Martin Sebor Opened: 2000-07-28 Last modified: 2008-09-26

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Discussion:

27.7.2.2, p1 uses a C-style cast rather than the more appropriate const_cast<> in the Returns clause for basic_istringstream<>::rdbuf(). The same C-style cast is being used in 27.7.3.2, p1, D.7.2.2, p1, and D.7.3.2, p1, and perhaps elsewhere. 27.7.6, p1 and D.7.2.2, p1 are missing the cast altogether.

C-style casts have not been deprecated, so the first part of this issue is stylistic rather than a matter of correctness.

Proposed resolution:

In 27.7.2.2, p1 replace

      -1- Returns: (basic_stringbuf<charT,traits,Allocator>*)&sb.

with

      -1- Returns: const_cast<basic_stringbuf<charT,traits,Allocator>*>(&sb).

In 27.7.3.2, p1 replace

      -1- Returns: (basic_stringbuf<charT,traits,Allocator>*)&sb.

with

      -1- Returns: const_cast<basic_stringbuf<charT,traits,Allocator>*>(&sb).

In 27.7.6, p1, replace

      -1- Returns: &sb

with

      -1- Returns: const_cast<basic_stringbuf<charT,traits,Allocator>*>(&sb).

In D.7.2.2, p1 replace

      -2- Returns: &sb.

with

      -2- Returns: const_cast<strstreambuf*>(&sb).

### 253. valarray helper functions are almost entirely useless

Section: 26.6.2.1 [valarray.cons], 26.6.2.2 [valarray.assign] Status: CD1 Submitter: Robert Klarer Opened: 2000-07-31 Last modified: 2008-09-26

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Discussion:

This discussion is adapted from message c++std-lib-7056 posted November 11, 1999. I don't think that anyone can reasonably claim that the problem described below is NAD.

These valarray constructors can never be called:

       template <class T>
             valarray<T>::valarray(const slice_array<T> &);
       template <class T>
             valarray<T>::valarray(const gslice_array<T> &);
       template <class T>
             valarray<T>::valarray(const mask_array<T> &);
       template <class T>
             valarray<T>::valarray(const indirect_array<T> &);

Similarly, these valarray assignment operators cannot be called:

         template <class T>
         valarray<T> valarray<T>::operator=(const slice_array<T> &);
         template <class T>
         valarray<T> valarray<T>::operator=(const gslice_array<T> &);
         template <class T>
         valarray<T> valarray<T>::operator=(const mask_array<T> &);
         template <class T>
         valarray<T> valarray<T>::operator=(const indirect_array<T> &);

Please consider the following example:

       #include <valarray>
       using namespace std;

       int main()
       {
           valarray<double> va1(12);
           valarray<double> va2(va1[slice(1,4,3)]); // line 1
       }

Since the valarray va1 is non-const, the result of the sub-expression va1[slice(1,4,3)] at line 1 is an rvalue of type const std::slice_array<double>. This slice_array rvalue is then used to construct va2. The constructor that is used to construct va2 is declared like this:

         template <class T>
         valarray<T>::valarray(const slice_array<T> &);

Notice the constructor's const reference parameter. When the constructor is called, a slice_array must be bound to this reference. The rules for binding an rvalue to a const reference are in 8.5.3, paragraph 5 (see also 13.3.3.1.4). Specifically, paragraph 5 indicates that a second slice_array rvalue is constructed (in this case copy-constructed) from the first one; it is this second rvalue that is bound to the reference parameter. Paragraph 5 also requires that the constructor that is used for this purpose be callable, regardless of whether the second rvalue is elided. The copy-constructor in this case is not callable, however, because it is private. Therefore, the compiler should report an error.

Since slice_arrays are always rvalues, the valarray constructor that has a parameter of type const slice_array<T> & can never be called. The same reasoning applies to the three other constructors and the four assignment operators that are listed at the beginning of this post. Furthermore, since these functions cannot be called, the valarray helper classes are almost entirely useless.

Proposed resolution:

slice_array:

- Make the copy constructor and copy-assignment operator declarations public in the slice_array class template definition in 26.6.5 [template.slice.array]
- remove paragraph 3 of 26.6.5 [template.slice.array]
- remove the copy constructor declaration from [cons.slice.arr]
- change paragraph 1 of [cons.slice.arr] to read "This constructor is declared to be private. This constructor need not be defined."
- remove the first sentence of paragraph 1 of 26.6.5.1 [slice.arr.assign]
- Change the first three words of the second sentence of paragraph 1 of 26.6.5.1 [slice.arr.assign] to "These assignment operators have"

gslice_array:

- Make the copy constructor and copy-assignment operator declarations public in the gslice_array class template definition in 26.6.7 [template.gslice.array]
- remove the note in paragraph 3 of 26.6.7 [template.gslice.array]
- remove the copy constructor declaration from [gslice.array.cons]
- change paragraph 1 of [gslice.array.cons] to read "This constructor is declared to be private. This constructor need not be defined."
- remove the first sentence of paragraph 1 of 26.6.7.1 [gslice.array.assign]
- Change the first three words of the second sentence of paragraph 1 of 26.6.7.1 [gslice.array.assign] to "These assignment operators have"

mask_array:

- Make the copy constructor and copy-assignment operator declarations public in the mask_array class template definition in 26.6.8 [template.mask.array]
- remove the note in paragraph 2 of 26.6.8 [template.mask.array]
- remove the copy constructor declaration from [mask.array.cons]
- change paragraph 1 of [mask.array.cons] to read "This constructor is declared to be private. This constructor need not be defined."
- remove the first sentence of paragraph 1 of 26.6.8.1 [mask.array.assign]
- Change the first three words of the second sentence of paragraph 1 of 26.6.8.1 [mask.array.assign] to "These assignment operators have"

indirect_array:

- Make the copy constructor and copy-assignment operator declarations public in the indirect_array class definition in 26.6.9 [template.indirect.array]
- remove the note in paragraph 2 of 26.6.9 [template.indirect.array]
- remove the copy constructor declaration from [indirect.array.cons]
- change the descriptive text in [indirect.array.cons] to read "This constructor is declared to be private. This constructor need not be defined."
- remove the first sentence of paragraph 1 of 26.6.9.1 [indirect.array.assign]
- Change the first three words of the second sentence of paragraph 1 of 26.6.9.1 [indirect.array.assign] to "These assignment operators have"

[Proposed resolution was modified in Santa Cruz: explicitly make copy constructor and copy assignment operators public, instead of removing them.]

Rationale:

Keeping the valarray constructors private is untenable. Merely making valarray a friend of the helper classes isn't good enough, because access to the copy constructor is checked in the user's environment.

Making the assignment operator public is not strictly necessary to solve this problem. A majority of the LWG (straw poll: 13-4) believed we should make the assignment operators public, in addition to the copy constructors, for reasons of symmetry and user expectation.

### 254. Exception types in clause 19 are constructed from `std::string`

Section: 19.2 [std.exceptions], 27.5.2.1.1 [ios::failure] Status: CD1 Submitter: Dave Abrahams Opened: 2000-08-01 Last modified: 2008-09-26

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Discussion:

Many of the standard exception types which implementations are required to throw are constructed with a const std::string& parameter. For example:

         19.1.5  Class out_of_range                          [lib.out.of.range]
         namespace std {
           class out_of_range : public logic_error {
           public:
             explicit out_of_range(const string& what_arg);
           };
         }

       1 The class out_of_range defines the type of objects  thrown  as  excep-
         tions to report an argument value not in its expected range.

         out_of_range(const string& what_arg);

         Effects:
           Constructs an object of class out_of_range.
         Postcondition:
           strcmp(what(), what_arg.c_str()) == 0.

There are at least two problems with this:

1. A program which is low on memory may end up throwing std::bad_alloc instead of out_of_range because memory runs out while constructing the exception object.
2. An obvious implementation which stores a std::string data member may end up invoking terminate() during exception unwinding because the exception object allocates memory (or rather fails to) as it is being copied.

There may be no cure for (1) other than changing the interface to out_of_range, though one could reasonably argue that (1) is not a defect. Personally I don't care that much if out-of-memory is reported when I only have 20 bytes left, in the case when out_of_range would have been reported. People who use exception-specifications might care a lot, though.

There is a cure for (2), but it isn't completely obvious. I think a note for implementors should be made in the standard. Avoiding possible termination in this case shouldn't be left up to chance. The cure is to use a reference-counted "string" implementation in the exception object. I am not necessarily referring to a std::string here; any simple reference-counting scheme for a NTBS would do.

Further discussion, in email:

...I'm not so concerned about (1). After all, a library implementation can add const char* constructors as an extension, and users don't need to avail themselves of the standard exceptions, though this is a lame position to be forced into. FWIW, std::exception and std::bad_alloc don't require a temporary basic_string.

...I don't think the fixed-size buffer is a solution to the problem, strictly speaking, because you can't satisfy the postcondition
`strcmp(what(), what_arg.c_str()) == 0`
For all values of what_arg (i.e. very long values). That means that the only truly conforming solution requires a dynamic allocation.

Further discussion, from Redmond:

The most important progress we made at the Redmond meeting was realizing that there are two separable issues here: the const string& constructor, and the copy constructor. If a user writes something like `throw std::out_of_range("foo")`, the const string& constructor is invoked before anything gets thrown. The copy constructor is potentially invoked during stack unwinding.

The copy constructor is a more serious problem, becuase failure during stack unwinding invokes `terminate`. The copy constructor must be nothrow. Curaçao: Howard thinks this requirement may already be present.

The fundamental problem is that it's difficult to get the nothrow requirement to work well with the requirement that the exception objects store a string of unbounded size, particularly if you also try to make the const string& constructor nothrow. Options discussed include:

- Limit the size of a string that exception objects are required to throw: change the postconditions of 19.2.2 [domain.error] paragraph 3 and 19.2.6 [runtime.error] paragraph 3 to something like this: "strncmp(what(), what_arg._str(), N) == 0, where N is an implementation defined constant no smaller than 256".
- Allow the const string& constructor to throw, but not the copy constructor. It's the implementor's responsibility to get it right. (An implementor might use a simple refcount class.)
- Compromise between the two: an implementation is not allowed to throw if the string's length is less than some N, but, if it doesn't throw, the string must compare equal to the argument.
- Add a new constructor that takes a const char*

(Not all of these options are mutually exclusive.)

Proposed resolution:

Change 19.2.1 [logic.error]

>     namespace std {
>       class logic_error : public exception {
>       public:
>         explicit logic_error(const string& what_arg);
>         explicit logic_error(const char* what_arg);
>       };
>     }

> ...

> `logic_error(const char* what_arg);`

> > -4- Effects: Constructs an object of class `logic_error`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.2 [domain.error]

>     namespace std {
>       class domain_error : public logic_error {
>       public:
>         explicit domain_error(const string& what_arg);
>         explicit domain_error(const char* what_arg);
>       };
>     }

> ...

> `domain_error(const char* what_arg);`

> > -4- Effects: Constructs an object of class `domain_error`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.3 [invalid.argument]

>     namespace std {
>       class invalid_argument : public logic_error {
>       public:
>         explicit invalid_argument(const string& what_arg);
>         explicit invalid_argument(const char* what_arg);
>       };
>     }

> ...

> `invalid_argument(const char* what_arg);`

> > -4- Effects: Constructs an object of class `invalid_argument`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.4 [length.error]

>     namespace std {
>       class length_error : public logic_error {
>       public:
>         explicit length_error(const string& what_arg);
>         explicit length_error(const char* what_arg);
>       };
>     }

> ...

> `length_error(const char* what_arg);`

> > -4- Effects: Constructs an object of class `length_error`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.5 [out.of.range]

>     namespace std {
>       class out_of_range : public logic_error {
>       public:
>         explicit out_of_range(const string& what_arg);
>         explicit out_of_range(const char* what_arg);
>       };
>     }

> ...

> `out_of_range(const char* what_arg);`

> > -4- Effects: Constructs an object of class `out_of_range`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.6 [runtime.error]

>     namespace std {
>       class runtime_error : public exception {
>       public:
>         explicit runtime_error(const string& what_arg);
>         explicit runtime_error(const char* what_arg);
>       };
>     }

> ...

> `runtime_error(const char* what_arg);`

> > -4- Effects: Constructs an object of class `runtime_error`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.7 [range.error]

>     namespace std {
>       class range_error : public runtime_error {
>       public:
>         explicit range_error(const string& what_arg);
>         explicit range_error(const char* what_arg);
>       };
>     }

> ...

> `range_error(const char* what_arg);`

> > -4- Effects: Constructs an object of class `range_error`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.8 [overflow.error]

>     namespace std {
>       class overflow_error : public runtime_error {
>       public:
>         explicit overflow_error(const string& what_arg);
>         explicit overflow_error(const char* what_arg);
>       };
>     }

> ...

> `overflow_error(const char* what_arg);`

> > -4- Effects: Constructs an object of class `overflow_error`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 19.2.9 [underflow.error]

>     namespace std {
>       class underflow_error : public runtime_error {
>       public:
>         explicit underflow_error(const string& what_arg);
>         explicit underflow_error(const char* what_arg);
>       };
>     }

> ...

> `underflow_error(const char* what_arg);`

> > -4- Effects: Constructs an object of class `underflow_error`.

> > -5- Postcondition: `strcmp(what(), what_arg) == 0`.

Change 27.5.2.1.1 [ios::failure]

>     namespace std {
>       class ios_base::failure : public exception {
>       public:
>         explicit failure(const string& msg);
>         explicit failure(const char* msg);
>         virtual const char* what() const throw();
>     };
>     }

> ...

> `failure(const char* msg);`

> > -4- Effects: Constructs an object of class `failure`.

> > -5- Postcondition: `strcmp(what(), msg) == 0`.

Rationale:

Throwing a bad_alloc while trying to construct a message for another exception-derived class is not necessarily a bad thing. And the bad_alloc constructor already has a no throw spec on it (18.4.2.1).

Future:

All involved would like to see const char* constructors added, but this should probably be done for C++0X as opposed to a DR.

I believe the no throw specs currently decorating these functions could be improved by some kind of static no throw spec checking mechanism (in a future C++ language). As they stand, the copy constructors might fail via a call to unexpected. I think what is intended here is that the copy constructors can't fail.

[Pre-Sydney: reopened at the request of Howard Hinnant. Post-Redmond: James Kanze noticed that the copy constructors of exception-derived classes do not have nothrow clauses. Those classes have no copy constructors declared, meaning the compiler-generated implicit copy constructors are used, and those compiler-generated constructors might in principle throw anything.]

[ Batavia: Merged copy constructor and assignment operator spec into `exception` and added `ios::failure` into the proposed resolution. ]

[ Oxford: The proposed resolution simply addresses the issue of constructing the exception objects with `const char*` and string literals without the need to explicit include or construct a `std::string`. ]

### 256. typo in 27.4.4.2, p17: copy_event does not exist

Section: 27.5.4.2 [basic.ios.members] Status: CD1 Submitter: Martin Sebor Opened: 2000-08-21 Last modified: 2008-09-26

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Discussion:

27.4.4.2, p17 says

> -17- Before copying any parts of rhs, calls each registered callback pair (fn,index) as (*fn)(erase_event,*this,index). After all parts but exceptions() have been replaced, calls each callback pair that was copied from rhs as (*fn)(copy_event,*this,index).

The name copy_event isn't defined anywhere. The intended name was copyfmt_event.

Proposed resolution:

Replace copy_event with copyfmt_event in the named paragraph.

### 258. Missing allocator requirement

Section: 20.2.2 [allocator.requirements] Status: CD1 Submitter: Matt Austern Opened: 2000-08-22 Last modified: 2008-09-26

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Discussion:

From lib-7752:

I've been assuming (and probably everyone else has been assuming) that allocator instances have a particular property, and I don't think that property can be deduced from anything in Table 32.

I think we have to assume that allocator type conversion is a homomorphism. That is, if x1 and x2 are of type X, where X::value_type is T, and if type Y is X::template rebind<U>::other, then Y(x1) == Y(x2) if and only if x1 == x2.

Further discussion: Howard Hinnant writes, in lib-7757:

I think I can prove that this is not provable by Table 32. And I agree it needs to be true except for the "and only if". If x1 != x2, I see no reason why it can't be true that Y(x1) == Y(x2). Admittedly I can't think of a practical instance where this would happen, or be valuable. But I also don't see a need to add that extra restriction. I think we only need:

> if (x1 == x2) then Y(x1) == Y(x2)

If we decide that == on allocators is transitive, then I think I can prove the above. But I don't think == is necessarily transitive on allocators. That is:

Given x1 == x2 and x2 == x3, this does not mean x1 == x3.

Example:

> x1 can deallocate pointers from: x1, x2, x3
> x2 can deallocate pointers from: x1, x2, x4
> x3 can deallocate pointers from: x1, x3
> x4 can deallocate pointers from: x2, x4

> x1 == x2, and x2 == x4, but x1 != x4

[Toronto: LWG members offered multiple opinions. One opinion is that it should not be required that `x1 == x2` implies `Y(x1) == Y(x2)`, and that it should not even be required that `X(x1) == x1`. Another opinion is that the second line from the bottom in table 32 already implies the desired property. This issue should be considered in light of other issues related to allocator instances.]

Proposed resolution:

Accept proposed wording from N2436 part 3.

[Lillehammer: Same conclusion as before: this should be considered as part of an allocator redesign, not solved on its own.]

[ Batavia: An allocator redesign is not forthcoming and thus we fixed this one issue. ]

[ Toronto: Reopened at the request of the project editor (Pete) because the proposed wording did not fit within the indicated table. The intent of the resolution remains unchanged. Pablo to work with Pete on improved wording. ]

[ Kona (2007): The LWG adopted the proposed resolution of N2387 for this issue which was subsequently split out into a separate paper N2436 for the purposes of voting. The resolution in N2436 addresses this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 259. `basic_string::operator[]` and const correctness

Section: 21.4.4 [string.capacity] Status: CD1 Submitter: Chris Newton Opened: 2000-08-27 Last modified: 2008-09-26

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Discussion:

Paraphrased from a message that Chris Newton posted to comp.std.c++:

The standard's description of `basic_string<>::operator[]` seems to violate const correctness.

The standard (21.3.4/1) says that "If `pos < size()`, returns `data()[pos]`." The types don't work. The return value of `data()` is `const charT*`, but `operator[]` has a non-const version whose return type is `reference`.

Proposed resolution:

In section 21.3.4, paragraph 1, change "`data()[pos]`" to "`*(begin() + pos)`".

### 260. Inconsistent return type of `istream_iterator::operator++(int)`

Section: 24.6.1.2 [istream.iterator.ops] Status: CD1 Submitter: Martin Sebor Opened: 2000-08-27 Last modified: 2008-09-26

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Discussion:

The synopsis of istream_iterator::operator++(int) in 24.5.1 shows it as returning the iterator by value. 24.5.1.2, p5 shows the same operator as returning the iterator by reference. That's incorrect given the Effects clause below (since a temporary is returned). The `&' is probably just a typo.

Proposed resolution:

Change the declaration in 24.5.1.2, p5 from

     istream_iterator<T,charT,traits,Distance>& operator++(int);

to

     istream_iterator<T,charT,traits,Distance> operator++(int);

(that is, remove the `&').

### 261. Missing description of `istream_iterator::operator!=`

Section: 24.6.1.2 [istream.iterator.ops] Status: CD1 Submitter: Martin Sebor Opened: 2000-08-27 Last modified: 2008-09-26

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Discussion:

24.5.1, p3 lists the synopsis for

       template <class T, class charT, class traits, class Distance>
            bool operator!=(const istream_iterator<T,charT,traits,Distance>& x,
                            const istream_iterator<T,charT,traits,Distance>& y);

but there is no description of what the operator does (i.e., no Effects or Returns clause) in 24.5.1.2.

Proposed resolution:

Add paragraph 7 to the end of section 24.5.1.2 with the following text:

       template <class T, class charT, class traits, class Distance>
            bool operator!=(const istream_iterator<T,charT,traits,Distance>& x,
                            const istream_iterator<T,charT,traits,Distance>& y);

-7- Returns: !(x == y).

### 262. Bitmask operator ~ specified incorrectly

Section: 17.5.2.1.3 [bitmask.types] Status: CD1 Submitter: Beman Dawes Opened: 2000-09-03 Last modified: 2008-09-26

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Discussion:

The ~ operation should be applied after the cast to int_type.

Proposed resolution:

Change 17.3.2.1.2 [lib.bitmask.types] operator~ from:

       bitmask operator~ ( bitmask X )
         { return static_cast< bitmask>(static_cast<int_type>(~ X)); }

to:

       bitmask operator~ ( bitmask X )
         { return static_cast< bitmask>(~static_cast<int_type>(X)); }

### 263. Severe restriction on `basic_string` reference counting

Section: 21.4 [basic.string] Status: CD1 Submitter: Kevlin Henney Opened: 2000-09-04 Last modified: 2008-09-26

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Discussion:

The note in paragraph 6 suggests that the invalidation rules for references, pointers, and iterators in paragraph 5 permit a reference- counted implementation (actually, according to paragraph 6, they permit a "reference counted implementation", but this is a minor editorial fix).

However, the last sub-bullet is so worded as to make a reference-counted implementation unviable. In the following example none of the conditions for iterator invalidation are satisfied:

        // first example: "*******************" should be printed twice
        string original = "some arbitrary text", copy = original;
        const string & alias = original;

        string::const_iterator i = alias.begin(), e = alias.end();
        for(string::iterator j = original.begin(); j != original.end(); ++j)
            *j = '*';
        while(i != e)
            cout << *i++;
        cout << endl;
        cout << original << endl;

Similarly, in the following example:

        // second example: "some arbitrary text" should be printed out
        string original = "some arbitrary text", copy = original;
        const string & alias = original;

        string::const_iterator i = alias.begin();
        original.begin();
        while(i != alias.end())
            cout << *i++;

I have tested this on three string implementations, two of which were reference counted. The reference-counted implementations gave "surprising behavior" because they invalidated iterators on the first call to non-const begin since construction. The current wording does not permit such invalidation because it does not take into account the first call since construction, only the first call since various member and non-member function calls.

Proposed resolution:

Change the following sentence in 21.3 paragraph 5 from

> Subsequent to any of the above uses except the forms of insert() and erase() which return iterators, the first call to non-const member functions operator[](), at(), begin(), rbegin(), end(), or rend().

to

> Following construction or any of the above uses, except the forms of insert() and erase() that return iterators, the first call to non- const member functions operator[](), at(), begin(), rbegin(), end(), or rend().

### 264. Associative container `insert(i, j)` complexity requirements are not feasible.

Section: 23.2.4 [associative.reqmts] Status: CD1 Submitter: John Potter Opened: 2000-09-07 Last modified: 2008-09-26

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Duplicate of: 102

Discussion:

Table 69 requires linear time if [i, j) is sorted. Sorted is necessary but not sufficient. Consider inserting a sorted range of even integers into a set<int> containing the odd integers in the same range.

Related issue: 102

Proposed resolution:

In Table 69, in section 23.1.2, change the complexity clause for insertion of a range from "N log(size() + N) (N is the distance from i to j) in general; linear if [i, j) is sorted according to value_comp()" to "N log(size() + N), where N is the distance from i to j".

[Copenhagen: Minor fix in proposed resolution: fixed unbalanced parens in the revised wording.]

Rationale:

Testing for valid insertions could be less efficient than simply inserting the elements when the range is not both sorted and between two adjacent existing elements; this could be a QOI issue.

The LWG considered two other options: (a) specifying that the complexity was linear if [i, j) is sorted according to value_comp() and between two adjacent existing elements; or (b) changing to Klog(size() + N) + (N - K) (N is the distance from i to j and K is the number of elements which do not insert immediately after the previous element from [i, j) including the first). The LWG felt that, since we can't guarantee linear time complexity whenever the range to be inserted is sorted, it's more trouble than it's worth to say that it's linear in some special cases.

### 265. std::pair::pair() effects overly restrictive

Section: 20.3.4 [pairs] Status: CD1 Submitter: Martin Sebor Opened: 2000-09-11 Last modified: 2008-09-26

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Discussion:

I don't see any requirements on the types of the elements of the std::pair container in 20.2.2. From the descriptions of the member functions it appears that they must at least satisfy the requirements of 20.1.3 [lib.copyconstructible] and 20.1.4 [lib.default.con.req], and in the case of the [in]equality operators also the requirements of 20.1.1 [lib.equalitycomparable] and 20.1.2 [lib.lessthancomparable].

I believe that the the CopyConstructible requirement is unnecessary in the case of 20.2.2, p2.

Proposed resolution:

Change the Effects clause in 20.2.2, p2 from

> -2- Effects: Initializes its members as if implemented: `pair() : first(T1()), second(T2()) {}`

to

> -2- Effects: Initializes its members as if implemented: `pair() : first(), second() {}`

Rationale:

The existing specification of pair's constructor appears to be a historical artifact: there was concern that pair's members be properly zero-initialized when they are built-in types. At one time there was uncertainty about whether they would be zero-initialized if the default constructor was written the obvious way. This has been clarified by core issue 178, and there is no longer any doubt that the straightforward implementation is correct.

### 266. bad_exception::~bad_exception() missing Effects clause

Section: 18.8.2.1 [bad.exception] Status: CD1 Submitter: Martin Sebor Opened: 2000-09-24 Last modified: 2008-09-26

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Discussion:

The synopsis for std::bad_exception lists the function ~bad_exception() but there is no description of what the function does (the Effects clause is missing).

Proposed resolution:

Remove the destructor from the class synopses of `bad_alloc` (18.6.2.1 [bad.alloc]), `bad_cast` (18.7.2 [bad.cast]), `bad_typeid` (18.7.3 [bad.typeid]), and `bad_exception` (18.8.2.1 [bad.exception]).

Rationale:

This is a general problem with the exception classes in clause 18. The proposed resolution is to remove the destructors from the class synopses, rather than to document the destructors' behavior, because removing them is more consistent with how exception classes are described in clause 19.

### 268. Typo in locale synopsis

Section: 22.3.1 [locale] Status: CD1 Submitter: Martin Sebor Opened: 2000-10-05 Last modified: 2008-09-26

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Discussion:

The synopsis of the class std::locale in 22.1.1 contains two typos: the semicolons after the declarations of the default ctor locale::locale() and the copy ctor locale::locale(const locale&) are missing.

Proposed resolution:

Add the missing semicolons, i.e., change

        //  construct/copy/destroy:
            locale() throw()
            locale(const locale& other) throw()

in the synopsis in 22.1.1 to

        //  construct/copy/destroy:
            locale() throw();
            locale(const locale& other) throw();

### 270. Binary search requirements overly strict

Section: 25.4.3 [alg.binary.search] Status: CD1 Submitter: Matt Austern Opened: 2000-10-18 Last modified: 2008-09-26

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Duplicate of: 472

Discussion:

Each of the four binary search algorithms (lower_bound, upper_bound, equal_range, binary_search) has a form that allows the user to pass a comparison function object. According to 25.3, paragraph 2, that comparison function object has to be a strict weak ordering.

This requirement is slightly too strict. Suppose we are searching through a sequence containing objects of type X, where X is some large record with an integer key. We might reasonably want to look up a record by key, in which case we would want to write something like this:

        struct key_comp {
          bool operator()(const X& x, int n) const {
            return x.key() < n;
          }
        }

        std::lower_bound(first, last, 47, key_comp());

key_comp is not a strict weak ordering, but there is no reason to prohibit its use in lower_bound.

There's no difficulty in implementing lower_bound so that it allows the use of something like key_comp. (It will probably work unless an implementor takes special pains to forbid it.) What's difficult is formulating language in the standard to specify what kind of comparison function is acceptable. We need a notion that's slightly more general than that of a strict weak ordering, one that can encompass a comparison function that involves different types. Expressing that notion may be complicated.

Additional questions raised at the Toronto meeting:

- Do we really want to specify what ordering the implementor must use when calling the function object? The standard gives specific expressions when describing these algorithms, but it also says that other expressions (with different argument order) are equivalent.
- If we are specifying ordering, note that the standard uses both orderings when describing `equal_range`.
- Are we talking about requiring these algorithms to work properly when passed a binary function object whose two argument types are not the same, or are we talking about requirements when they are passed a binary function object with several overloaded versions of `operator()`?
- The definition of a strict weak ordering does not appear to give any guidance on issues of overloading; it only discusses expressions, and all of the values in these expressions are of the same type. Some clarification would seem to be in order.

Additional discussion from Copenhagen:

- It was generally agreed that there is a real defect here: if the predicate is merely required to be a Strict Weak Ordering, then it's possible to pass in a function object with an overloaded operator(), where the version that's actually called does something completely inappropriate. (Such as returning a random value.)
- An alternative formulation was presented in a paper distributed by David Abrahams at the meeting, "Binary Search with Heterogeneous Comparison", J16-01/0027 = WG21 N1313: Instead of viewing the predicate as a Strict Weak Ordering acting on a sorted sequence, view the predicate/value pair as something that partitions a sequence. This is almost equivalent to saying that we should view binary search as if we are given a unary predicate and a sequence, such that f(*p) is true for all p below a specific point and false for all p above it. The proposed resolution is based on that alternative formulation.

Proposed resolution:

Change 25.3 [lib.alg.sorting] paragraph 3 from:

> 3 For all algorithms that take Compare, there is a version that uses operator< instead. That is, comp(*i, *j) != false defaults to *i < *j != false. For the algorithms to work correctly, comp has to induce a strict weak ordering on the values.

to:

> 3 For all algorithms that take Compare, there is a version that uses operator< instead. That is, comp(*i, *j) != false defaults to *i < *j != false. For algorithms other than those described in lib.alg.binary.search (25.3.3) to work correctly, comp has to induce a strict weak ordering on the values.

Add the following paragraph after 25.3 [lib.alg.sorting] paragraph 5:

> -6- A sequence [start, finish) is partitioned with respect to an expression f(e) if there exists an integer n such that for all 0 <= i < distance(start, finish), f(*(begin+i)) is true if and only if i < n.

Change 25.3.3 [lib.alg.binary.search] paragraph 1 from:

> -1- All of the algorithms in this section are versions of binary search and assume that the sequence being searched is in order according to the implied or explicit comparison function. They work on non-random access iterators minimizing the number of comparisons, which will be logarithmic for all types of iterators. They are especially appropriate for random access iterators, because these algorithms do a logarithmic number of steps through the data structure. For non-random access iterators they execute a linear number of steps.

to:

> -1- All of the algorithms in this section are versions of binary search and assume that the sequence being searched is partitioned with respect to an expression formed by binding the search key to an argument of the implied or explicit comparison function. They work on non-random access iterators minimizing the number of comparisons, which will be logarithmic for all types of iterators. They are especially appropriate for random access iterators, because these algorithms do a logarithmic number of steps through the data structure. For non-random access iterators they execute a linear number of steps.

Change 25.3.3.1 [lib.lower.bound] paragraph 1 from:

> -1- Requires: Type T is LessThanComparable (lib.lessthancomparable).

to:

> -1- Requires: The elements e of [first, last) are partitioned with respect to the expression e < value or comp(e, value)

Remove 25.3.3.1 [lib.lower.bound] paragraph 2:

> -2- Effects: Finds the first position into which value can be inserted without violating the ordering.

Change 25.3.3.2 [lib.upper.bound] paragraph 1 from:

> -1- Requires: Type T is LessThanComparable (lib.lessthancomparable).

to:

> -1- Requires: The elements e of [first, last) are partitioned with respect to the expression !(value < e) or !comp(value, e)

Remove 25.3.3.2 [lib.upper.bound] paragraph 2:

> -2- Effects: Finds the furthermost position into which value can be inserted without violating the ordering.

Change 25.3.3.3 [lib.equal.range] paragraph 1 from:

> -1- Requires: Type T is LessThanComparable (lib.lessthancomparable).

to:

> -1- Requires: The elements e of [first, last) are partitioned with respect to the expressions e < value and !(value < e) or comp(e, value) and !comp(value, e). Also, for all elements e of [first, last), e < value implies !(value < e) or comp(e, value) implies !comp(value, e)

Change 25.3.3.3 [lib.equal.range] paragraph 2 from:

> -2- Effects: Finds the largest subrange [i, j) such that the value can be inserted at any iterator k in it without violating the ordering. k satisfies the corresponding conditions: !(*k < value) && !(value < *k) or comp(*k, value) == false && comp(value, *k) == false.

to:

       -2- Returns:
             make_pair(lower_bound(first, last, value),
                       upper_bound(first, last, value))
           or
             make_pair(lower_bound(first, last, value, comp),
                       upper_bound(first, last, value, comp))

Change 25.3.3.3 [lib.binary.search] paragraph 1 from:

> -1- Requires: Type T is LessThanComparable (lib.lessthancomparable).

to:

> -1- Requires: The elements e of [first, last) are partitioned with respect to the expressions e < value and !(value < e) or comp(e, value) and !comp(value, e). Also, for all elements e of [first, last), e < value implies !(value < e) or comp(e, value) implies !comp(value, e)

[Copenhagen: Dave Abrahams provided this wording]

[Redmond: Minor changes in wording. (Removed "non-negative", and changed the "other than those described in" wording.) Also, the LWG decided to accept the "optional" part.]

Rationale:

The proposed resolution reinterprets binary search. Instead of thinking about searching for a value in a sorted range, we view that as an important special case of a more general algorithm: searching for the partition point in a partitioned range.

We also add a guarantee that the old wording did not: we ensure that the upper bound is no earlier than the lower bound, that the pair returned by equal_range is a valid range, and that the first part of that pair is the lower bound.

### 271. basic_iostream missing typedefs

Section: 27.7.1.5 [iostreamclass] Status: CD1 Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2008-09-26

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Discussion:

Class template basic_iostream has no typedefs. The typedefs it inherits from its base classes can't be used, since (for example) basic_iostream<T>::traits_type is ambiguous.

Proposed resolution:

Add the following to basic_iostream's class synopsis in 27.7.1.5 [iostreamclass], immediately after `public`:

      // types:
      typedef charT                     char_type;
      typedef typename traits::int_type int_type;
      typedef typename traits::pos_type pos_type;
      typedef typename traits::off_type off_type;
      typedef traits                    traits_type;

### 272. Missing parentheses around subexpression

Section: 27.5.4.3 [iostate.flags] Status: CD1 Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2008-09-26

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Duplicate of: 569

Discussion:

27.4.4.3, p4 says about the postcondition of the function: If rdbuf()!=0 then state == rdstate(); otherwise rdstate()==state|ios_base::badbit.

The expression on the right-hand-side of the operator==() needs to be parenthesized in order for the whole expression to ever evaluate to anything but non-zero.

Proposed resolution:

Add parentheses like so: rdstate()==(state|ios_base::badbit).

### 273. Missing ios_base qualification on members of a dependent class

Section: 27 [input.output] Status: CD1 Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2008-09-26

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Discussion:

27.5.2.4.2, p4, and 27.8.1.6, p2, 27.8.1.7, p3, 27.8.1.9, p2, 27.8.1.10, p3 refer to in and/or out w/o ios_base:: qualification. That's incorrect since the names are members of a dependent base class (14.6.2 [temp.dep]) and thus not visible.

Proposed resolution:

Qualify the names with the name of the class of which they are members, i.e., ios_base.

### 274. a missing/impossible allocator requirement

Section: 20.2.2 [allocator.requirements] Status: CD1 Submitter: Martin Sebor Opened: 2000-11-02 Last modified: 2008-09-26

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Discussion:

I see that table 31 in 20.1.5, p3 allows T in std::allocator<T> to be of any type. But the synopsis in 20.4.1 calls for allocator<>::address() to be overloaded on reference and const_reference, which is ill-formed for all T = const U. In other words, this won't work:

template class std::allocator<const int>;

The obvious solution is to disallow specializations of allocators on const types. However, while containers' elements are required to be assignable (which rules out specializations on const T's), I think that allocators might perhaps be potentially useful for const values in other contexts. So if allocators are to allow const types a partial specialization of std::allocator<const T> would probably have to be provided.

Proposed resolution:

Change the text in row 1, column 2 of table 32 in 20.1.5, p3 from

> any type

to

> any non-const, non-reference type

[Redmond: previous proposed resolution was "any non-const, non-volatile, non-reference type". Got rid of the "non-volatile".]

Rationale:

Two resolutions were originally proposed: one that partially specialized std::allocator for const types, and one that said an allocator's value type may not be const. The LWG chose the second. The first wouldn't be appropriate, because allocators are intended for use by containers, and const value types don't work in containers. Encouraging the use of allocators with const value types would only lead to unsafe code.

The original text for proposed resolution 2 was modified so that it also forbids volatile types and reference types.

[Curaçao: LWG double checked and believes volatile is correctly excluded from the PR.]

### 275. Wrong type in num_get::get() overloads

Section: 22.4.2.1.1 [facet.num.get.members] Status: CD1 Submitter: Matt Austern Opened: 2000-11-02 Last modified: 2008-09-26

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Discussion:

In 22.2.2.1.1, we have a list of overloads for num_get<>::get(). There are eight overloads, all of which are identical except for the last parameter. The overloads are:

- long&
- unsigned short&
- unsigned int&
- unsigned long&
- short&
- double&
- long double&
- void*&

There is a similar list, in 22.2.2.1.2, of overloads for num_get<>::do_get(). In this list, the last parameter has the types:

- long&
- unsigned short&
- unsigned int&
- unsigned long&
- float&
- double&
- long double&
- void*&

These two lists are not identical. They should be, since `get` is supposed to call `do_get` with exactly the arguments it was given.

Proposed resolution:

In 22.4.2.1.1 [facet.num.get.members], change

      iter_type get(iter_type in, iter_type end, ios_base& str,
                    ios_base::iostate& err, short& val) const;

to

      iter_type get(iter_type in, iter_type end, ios_base& str,
                    ios_base::iostate& err, float& val) const;

### 276. Assignable requirement for container value type overly strict

Section: 23.2 [container.requirements] Status: CD1 Submitter: Peter Dimov Opened: 2000-11-07 Last modified: 2008-09-26

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Discussion:

23.1/3 states that the objects stored in a container must be Assignable. 23.4.1 [map], paragraph 2, states that map satisfies all requirements for a container, while in the same time defining value_type as pair<const Key, T> - a type that is not Assignable.

It should be noted that there exists a valid and non-contradictory interpretation of the current text. The wording in 23.1/3 avoids mentioning value_type, referring instead to "objects stored in a container." One might argue that map does not store objects of type map::value_type, but of map::mapped_type instead, and that the Assignable requirement applies to map::mapped_type, not map::value_type.

However, this makes map a special case (other containers store objects of type value_type) and the Assignable requirement is needlessly restrictive in general.

For example, the proposed resolution of active library issue 103 is to make set::iterator a constant iterator; this means that no set operations can exploit the fact that the stored objects are Assignable.

This is related to, but slightly broader than, closed issue 140.

Proposed resolution:

23.1/3: Strike the trailing part of the sentence:

> , and the additional requirements of Assignable types from 23.1/3

so that it reads:

> -3- The type of objects stored in these components must meet the requirements of CopyConstructible types (lib.copyconstructible).

23.1/4: Modify to make clear that this requirement is not for all containers. Change to:

> -4- Table 64 defines the Assignable requirement. Some containers require this property of the types to be stored in the container. T is the type used to instantiate the container. t is a value of T, and u is a value of (possibly const) T.

23.1, Table 65: in the first row, change "T is Assignable" to "T is CopyConstructible".

23.2.1/2: Add sentence for Assignable requirement. Change to:

> -2- A deque satisfies all of the requirements of a container and of a reversible container (given in tables in lib.container.requirements) and of a sequence, including the optional sequence requirements (lib.sequence.reqmts). In addition to the requirements on the stored object described in 23.1[lib.container.requirements], the stored object must also meet the requirements of Assignable. Descriptions are provided here only for operations on deque that are not described in one of these tables or for operations where there is additional semantic information.

23.2.2/2: Add Assignable requirement to specific methods of list. Change to:

> -2- A list satisfies all of the requirements of a container and of a reversible container (given in two tables in lib.container.requirements) and of a sequence, including most of the the optional sequence requirements (lib.sequence.reqmts). The exceptions are the operator[] and at member functions, which are not provided. [Footnote: These member functions are only provided by containers whose iterators are random access iterators. --- end foonote]

> list does not require the stored type T to be Assignable unless the following methods are instantiated: [Footnote: Implementors are permitted but not required to take advantage of T's Assignable properties for these methods. -- end foonote]

>          list<T,Allocator>& operator=(const list<T,Allocator>&  x );
>          template <class InputIterator>
>            void assign(InputIterator first, InputIterator last);
>          void assign(size_type n, const T& t);

> Descriptions are provided here only for operations on list that are not described in one of these tables or for operations where there is additional semantic information.

23.2.4/2: Add sentence for Assignable requirement. Change to:

> -2- A vector satisfies all of the requirements of a container and of a reversible container (given in two tables in lib.container.requirements) and of a sequence, including most of the optional sequence requirements (lib.sequence.reqmts). The exceptions are the push_front and pop_front member functions, which are not provided. In addition to the requirements on the stored object described in 23.1[lib.container.requirements], the stored object must also meet the requirements of Assignable. Descriptions are provided here only for operations on vector that are not described in one of these tables or for operations where there is additional semantic information.

Rationale:

list, set, multiset, map, multimap are able to store non-Assignables. However, there is some concern about `list<T>`: although in general there's no reason for T to be Assignable, some implementations of the member functions `operator=` and `assign` do rely on that requirement. The LWG does not want to forbid such implementations.

Note that the type stored in a standard container must still satisfy the requirements of the container's allocator; this rules out, for example, such types as "const int". See issue 274 for more details.

In principle we could also relax the "Assignable" requirement for individual `vector` member functions, such as `push_back`. However, the LWG did not see great value in such selective relaxation. Doing so would remove implementors' freedom to implement `vector::push_back` in terms of `vector::insert`.

### 278. What does iterator validity mean?

Section: 23.3.4.4 [list.ops] Status: CD1 Submitter: P.J. Plauger Opened: 2000-11-27 Last modified: 2008-09-30

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Discussion:

Section 23.3.4.4 [list.ops] states that

      void splice(iterator position, list<T, Allocator>& x);

invalidates all iterators and references to list `x`.

But what does the C++ Standard mean by "invalidate"? You can still dereference the iterator to a spliced list element, but you'd better not use it to delimit a range within the original list. For the latter operation, it has definitely lost some of its validity.

If we accept the proposed resolution to issue 250, then we'd better clarify that a "valid" iterator need no longer designate an element within the same container as it once did. We then have to clarify what we mean by invalidating a past-the-end iterator, as when a vector or string grows by reallocation. Clearly, such an iterator has a different kind of validity. Perhaps we should introduce separate terms for the two kinds of "validity."

Proposed resolution:

Add the following text to the end of section X [iterator.concepts], after paragraph 5:

> An invalid iterator is an iterator that may be singular. [Footnote: This definition applies to pointers, since pointers are iterators. The effect of dereferencing an iterator that has been invalidated is undefined.]

[post-Copenhagen: Matt provided wording.]

[Redmond: General agreement with the intent, some objections to the wording. Dave provided new wording.]

Rationale:

This resolution simply defines a term that the Standard uses but never defines, "invalid", in terms of a term that is defined, "singular".

Why do we say "may be singular", instead of "is singular"? That's becuase a valid iterator is one that is known to be nonsingular. Invalidating an iterator means changing it in such a way that it's no longer known to be nonsingular. An example: inserting an element into the middle of a vector is correctly said to invalidate all iterators pointing into the vector. That doesn't necessarily mean they all become singular.

### 280. Comparison of reverse_iterator to const reverse_iterator

Section: 24.5.1 [reverse.iterators] Status: CD1 Submitter: Steve Cleary Opened: 2000-11-27 Last modified: 2008-09-26

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Discussion:

This came from an email from Steve Cleary to Fergus in reference to issue 179. The library working group briefly discussed this in Toronto and believed it should be a separate issue. There was also some reservations about whether this was a worthwhile problem to fix.

Steve said: "Fixing reverse_iterator. std::reverse_iterator can (and should) be changed to preserve these additional requirements." He also said in email that it can be done without breaking user's code: "If you take a look at my suggested solution, reverse_iterator doesn't have to take two parameters; there is no danger of breaking existing code, except someone taking the address of one of the reverse_iterator global operator functions, and I have to doubt if anyone has ever done that. . . But, just in case they have, you can leave the old global functions in as well -- they won't interfere with the two-template-argument functions. With that, I don't see how any user code could break."

Proposed resolution:

Section: 24.5.1.1 [reverse.iterator] add/change the following declarations:

      A) Add a templated assignment operator, after the same manner
            as the templated copy constructor, i.e.:

      template < class U >
      reverse_iterator < Iterator >& operator=(const reverse_iterator< U >& u);

      B) Make all global functions (except the operator+) have
      two template parameters instead of one, that is, for
      operator ==, !=, <, >, <=, >=, - replace:

           template < class Iterator >
           typename reverse_iterator< Iterator >::difference_type operator-(
                     const reverse_iterator< Iterator >& x,
                     const reverse_iterator< Iterator >& y);

      with:

          template < class Iterator1, class Iterator2 >
          typename reverse_iterator < Iterator1 >::difference_type operator-(
                     const reverse_iterator < Iterator1 > & x,
                     const reverse_iterator < Iterator2 > & y);

Also make the addition/changes for these signatures in 24.5.1.3 [reverse.iter.ops].

[ Copenhagen: The LWG is concerned that the proposed resolution introduces new overloads. Experience shows that introducing overloads is always risky, and that it would be inappropriate to make this change without implementation experience. It may be desirable to provide this feature in a different way. ]

[ Lillehammer: We now have implementation experience, and agree that this solution is safe and correct. ]

### 281. std::min() and max() requirements overly restrictive

Section: 25.4.7 [alg.min.max] Status: CD1 Submitter: Martin Sebor Opened: 2000-12-02 Last modified: 2008-09-26

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Duplicate of: 486

Discussion:

The requirements in 25.3.7, p1 and 4 call for T to satisfy the requirements of `LessThanComparable` ( [lessthancomparable]) and `CopyConstructible` (20.2.1 [utility.arg.requirements]). Since the functions take and return their arguments and result by const reference, I believe the `CopyConstructible` requirement is unnecessary.

Proposed resolution:

Remove the `CopyConstructible` requirement. Specifically, replace 25.3.7, p1 with

-1- Requires: Type T is `LessThanComparable` ( [lessthancomparable]).

and replace 25.3.7, p4 with

-4- Requires: Type T is `LessThanComparable` ( [lessthancomparable]).

### 282. What types does numpunct grouping refer to?

Section: 22.4.2.2.2 [facet.num.put.virtuals] Status: CD1 Submitter: Howard Hinnant Opened: 2000-12-05 Last modified: 2008-09-26

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Discussion:

Paragraph 16 mistakenly singles out integral types for inserting thousands_sep() characters. This conflicts with the syntax for floating point numbers described under 22.2.3.1/2.

Proposed resolution:

Change paragraph 16 from:

> For integral types, punct.thousands_sep() characters are inserted into the sequence as determined by the value returned by punct.do_grouping() using the method described in 22.4.3.1.2 [facet.numpunct.virtuals].

To:

> For arithmetic types, punct.thousands_sep() characters are inserted into the sequence as determined by the value returned by punct.do_grouping() using the method described in 22.4.3.1.2 [facet.numpunct.virtuals].

[ Copenhagen: Opinions were divided about whether this is actually an inconsistency, but at best it seems to have been unintentional. This is only an issue for floating-point output: The standard is unambiguous that implementations must parse thousands_sep characters when performing floating-point. The standard is also unambiguous that this requirement does not apply to the "C" locale. ]

[ A survey of existing practice is needed; it is believed that some implementations do insert thousands_sep characters for floating-point output and others fail to insert thousands_sep characters for floating-point input even though this is unambiguously required by the standard. ]

[Post-Curaçao: the above proposed resolution is the consensus of Howard, Bill, Pete, Benjamin, Nathan, Dietmar, Boris, and Martin.]

### 283. std::replace() requirement incorrect/insufficient

Section: 25.3.5 [alg.replace] Status: CD1 Submitter: Martin Sebor Opened: 2000-12-15 Last modified: 2008-09-26

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Duplicate of: 483

Discussion:

(revision of the further discussion) There are a number of problems with the requires clauses for the algorithms in 25.1 and 25.2. The requires clause of each algorithm should describe the necessary and sufficient requirements on the inputs to the algorithm such that the algorithm compiles and runs properly. Many of the requires clauses fail to do this. Here is a summary of the kinds of mistakes:

1. Use of EqualityComparable, which only puts requirements on a single type, when in fact an equality operator is required between two different types, typically either T and the iterator's value type or between the value types of two different iterators.
2. Use of Assignable for T when in fact what was needed is Assignable for the value_type of the iterator, and convertability from T to the value_type of the iterator. Or for output iterators, the requirement should be that T is writable to the iterator (output iterators do not have value types).

Here is the list of algorithms that contain mistakes:

- 25.1.2 std::find
- 25.1.6 std::count
- 25.1.8 std::equal
- 25.1.9 std::search, std::search_n
- 25.2.4 std::replace, std::replace_copy
- 25.2.5 std::fill
- 25.2.7 std::remove, std::remove_copy

Also, in the requirements for EqualityComparable, the requirement that the operator be defined for const objects is lacking.

Proposed resolution:

20.1.1 Change p1 from

In Table 28, `T` is a type to be supplied by a C++ program instantiating a template, `a`, `b`, and `c` are values of type `T`.

to

In Table 28, `T` is a type to be supplied by a C++ program instantiating a template, `a`, `b`, and `c` are values of type `const T`.

25 Between p8 and p9

Add the following sentence:

When the description of an algorithm gives an expression such as `*first == value` for a condition, it is required that the expression evaluate to either true or false in boolean contexts.

25.1.2 Change p1 by deleting the requires clause.

25.1.6 Change p1 by deleting the requires clause.

25.1.9

Change p4 from

-4- Requires: Type `T` is `EqualityComparable` (20.1.1), type Size is convertible to integral type (4.7.12.3).

to

-4- Requires: The type `Size` is convertible to integral type (4.7.12.3).

25.2.4 Change p1 from

-1- Requires: Type `T` is `Assignable` (23.1 ) (and, for `replace()`, `EqualityComparable` (20.1.1 )).

to

-1- Requires: The expression `*first = new_value` must be valid.

and change p4 from

-4- Requires: Type `T` is `Assignable` (23.1) (and, for `replace_copy()`, `EqualityComparable` (20.1.1)). The ranges `[first, last)` and `[result, result + (last - first))` shall not overlap.

to

-4- Requires: The results of the expressions `*first` and `new_value` must be writable to the result output iterator. The ranges `[first, last)` and `[result, result + (last - first))` shall not overlap.

25.2.5 Change p1 from

-1- Requires: Type `T` is `Assignable` (23.1). The type `Size` is convertible to an integral type (4.7.12.3).

to

-1- Requires: The expression `value` must be is writable to the output iterator. The type `Size` is convertible to an integral type (4.7.12.3).

25.2.7 Change p1 from

-1- Requires: Type `T` is `EqualityComparable` (20.1.1).

to

-1- Requires: The value type of the iterator must be `Assignable` (23.1).

Rationale:

The general idea of the proposed solution is to remove the faulty requires clauses and let the returns and effects clauses speak for themselves. That is, the returns clauses contain expressions that must be valid, and therefore already imply the correct requirements. In addition, a sentence is added at the beginning of chapter 25 saying that expressions given as conditions must evaluate to true or false in a boolean context. An alternative would be to say that the type of these condition expressions must be literally bool, but that would be imposing a greater restriction that what the standard currently says (which is convertible to bool).

### 284. unportable example in 20.3.7, p6

Section: 20.7.7 [comparisons] Status: CD1 Submitter: Martin Sebor Opened: 2000-12-26 Last modified: 2008-09-26

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Discussion:

The example in 20.7.7 [comparisons], p6 shows how to use the C library function `strcmp()` with the function pointer adapter `ptr_fun()`. But since it's unspecified whether the C library functions have `extern "C"` or `extern "C++"` linkage [17.6.2.3 [using.linkage]], and since function pointers with different the language linkage specifications (7.5 [dcl.link]) are incompatible, whether this example is well-formed is unspecified.

Proposed resolution:

Change 20.7.7 [comparisons] paragraph 6 from:

> [Example:

>         replace_if(v.begin(), v.end(), not1(bind2nd(ptr_fun(strcmp), "C")), "C++");

> replaces each `C` with `C++` in sequence `v`.

to:

> [Example:

>         int compare(const char*, const char*);
>         replace_if(v.begin(), v.end(),
>                    not1(bind2nd(ptr_fun(compare), "abc")), "def");

> replaces each `abc` with `def` in sequence `v`.

Also, remove footnote 215 in that same paragraph.

[Copenhagen: Minor change in the proposed resolution. Since this issue deals in part with C and C++ linkage, it was believed to be too confusing for the strings in the example to be "C" and "C++". ]

[Redmond: More minor changes. Got rid of the footnote (which seems to make a sweeping normative requirement, even though footnotes aren't normative), and changed the sentence after the footnote so that it corresponds to the new code fragment.]

### 285. minor editorial errors in fstream ctors

Section: 27.9.1.7 [ifstream.cons] Status: CD1 Submitter: Martin Sebor Opened: 2000-12-31 Last modified: 2008-09-26

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Discussion:

27.9.1.7 [ifstream.cons], p2, 27.9.1.11 [ofstream.cons], p2, and 27.9.1.15 [fstream.cons], p2 say about the effects of each constructor:

... If that function returns a null pointer, calls `setstate(failbit)` (which may throw `ios_base::failure`).

The parenthetical note doesn't apply since the ctors cannot throw an exception due to the requirement in 27.5.4.1 [basic.ios.cons], p3 that `exceptions()` be initialized to `ios_base::goodbit`.

Proposed resolution:

Strike the parenthetical note from the Effects clause in each of the paragraphs mentioned above.

### 286. <cstdlib> requirements missing size_t typedef

Section: 25.5 [alg.c.library] Status: CD1 Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2008-09-26

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Discussion:

The <cstdlib> header file contains prototypes for bsearch and qsort (C++ Standard section 25.4 paragraphs 3 and 4) and other prototypes (C++ Standard section 21.4 paragraph 1 table 49) that require the typedef size_t. Yet size_t is not listed in the <cstdlib> synopsis table 78 in section 25.4.

Proposed resolution:

Add the type size_t to Table 78 (section 25.4) and add the type size_t <cstdlib> to Table 97 (section C.2).

Rationale:

Since size_t is in <stdlib.h>, it must also be in <cstdlib>.

### 288. <cerrno> requirements missing macro EILSEQ

Section: 19.4 [errno] Status: CD1 Submitter: Judy Ward Opened: 2000-12-30 Last modified: 2008-09-26

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Discussion:

ISO/IEC 9899:1990/Amendment1:1994 Section 4.3 States: "The list of macros defined in <errno.h> is adjusted to include a new macro, EILSEQ"

ISO/IEC 14882:1998(E) section 19.3 does not refer to the above amendment.

Proposed resolution:

Update Table 26 (section 19.3) "Header <cerrno> synopsis" and Table 95 (section C.2) "Standard Macros" to include EILSEQ.

### 291. Underspecification of set algorithms

Section: 25.4.5 [alg.set.operations] Status: CD1 Submitter: Matt Austern Opened: 2001-01-03 Last modified: 2008-09-26

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Discussion:

The standard library contains four algorithms that compute set operations on sorted ranges: `set_union`, `set_intersection`, `set_difference`, and `set_symmetric_difference`. Each of these algorithms takes two sorted ranges as inputs, and writes the output of the appropriate set operation to an output range. The elements in the output range are sorted.

The ordinary mathematical definitions are generalized so that they apply to ranges containing multiple copies of a given element. Two elements are considered to be "the same" if, according to an ordering relation provided by the user, neither one is less than the other. So, for example, if one input range contains five copies of an element and another contains three, the output range of `set_union` will contain five copies, the output range of `set_intersection` will contain three, the output range of `set_difference` will contain two, and the output range of `set_symmetric_difference` will contain two.

Because two elements can be "the same" for the purposes of these set algorithms, without being identical in other respects (consider, for example, strings under case-insensitive comparison), this raises a number of unanswered questions:

- If we're copying an element that's present in both of the input ranges, which one do we copy it from?
- If there are n copies of an element in the relevant input range, and the output range will contain fewer copies (say m) which ones do we choose? The first m, or the last m, or something else?
- Are these operations stable? That is, does a run of equivalent elements appear in the output range in the same order as as it appeared in the input range(s)?

The standard should either answer these questions, or explicitly say that the answers are unspecified. I prefer the former option, since, as far as I know, all existing implementations behave the same way.

Proposed resolution:

Add the following to the end of 25.4.5.2 [set.union] paragraph 5:

> If [first1, last1) contains m elements that are equivalent to each other and [first2, last2) contains n elements that are equivalent to them, then max(m, n) of these elements will be copied to the output range: all m of these elements from [first1, last1), and the last max(n-m, 0) of them from [first2, last2), in that order.

Add the following to the end of 25.4.5.3 [set.intersection] paragraph 5:

> If [first1, last1) contains m elements that are equivalent to each other and [first2, last2) contains n elements that are equivalent to them, the first min(m, n) of those elements from [first1, last1) are copied to the output range.

Add a new paragraph, Notes, after 25.4.5.4 [set.difference] paragraph 4:

> If [first1, last1) contains m elements that are equivalent to each other and [first2, last2) contains n elements that are equivalent to them, the last max(m-n, 0) elements from [first1, last1) are copied to the output range.

Add a new paragraph, Notes, after 25.4.5.5 [set.symmetric.difference] paragraph 4:

> If [first1, last1) contains m elements that are equivalent to each other and [first2, last2) contains n elements that are equivalent to them, then |m - n| of those elements will be copied to the output range: the last m - n of these elements from [first1, last1) if m > n, and the last n - m of these elements from [first2, last2) if m < n.

[Santa Cruz: it's believed that this language is clearer than what's in the Standard. However, it's also believed that the Standard may already make these guarantees (although not quite in these words). Bill and Howard will check and see whether they think that some or all of these changes may be redundant. If so, we may close this issue as NAD.]

Rationale:

For simple cases, these descriptions are equivalent to what's already in the Standard. For more complicated cases, they describe the behavior of existing implementations.

### 292. effects of a.copyfmt (a)

Section: 27.5.4.2 [basic.ios.members] Status: CD1 Submitter: Martin Sebor Opened: 2001-01-05 Last modified: 2008-09-26

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Discussion:

The Effects clause of the member function `copyfmt()` in 27.4.4.2, p15 doesn't consider the case where the left-hand side argument is identical to the argument on the right-hand side, that is `(this == &rhs)`. If the two arguments are identical there is no need to copy any of the data members or call any callbacks registered with `register_callback()`. Also, as Howard Hinnant points out in message c++std-lib-8149 it appears to be incorrect to allow the object to fire `erase_event` followed by `copyfmt_event` since the callback handling the latter event may inadvertently attempt to access memory freed by the former.

Proposed resolution:

Change the Effects clause in 27.4.4.2, p15 from

> -15- Effects:Assigns to the member objects of `*this` the corresponding member objects of `rhs`, except that...

to

> -15- Effects:If `(this == &rhs)` does nothing. Otherwise assigns to the member objects of `*this` the corresponding member objects of `rhs`, except that...

### 294. User defined macros and standard headers

Section: 17.6.3.3.1 [macro.names] Status: CD1 Submitter: James Kanze Opened: 2001-01-11 Last modified: 2008-09-26

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Discussion:

Paragraph 2 of 17.6.3.3.1 [macro.names] reads: "A translation unit that includes a header shall not contain any macros that define names declared in that header." As I read this, it would mean that the following program is legal:

      #define npos 3.14
      #include <sstream>

since npos is not defined in <sstream>. It is, however, defined in <string>, and it is hard to imagine an implementation in which <sstream> didn't include <string>.

I think that this phrase was probably formulated before it was decided that a standard header may freely include other standard headers. The phrase would be perfectly appropriate for C, for example. In light of 17.6.4.2 [res.on.headers] paragraph 1, however, it isn't stringent enough.

Proposed resolution:

For 17.6.3.3.1 [macro.names], replace the current wording, which reads:

> Each name defined as a macro in a header is reserved to the implementation for any use if the translation unit includes the header.168)

> A translation unit that includes a header shall not contain any macros that define names declared or defined in that header. Nor shall such a translation unit define macros for names lexically identical to keywords.

> 168) It is not permissible to remove a library macro definition by using the #undef directive.

with the wording:

> A translation unit that includes a standard library header shall not #define or #undef names declared in any standard library header.

> A translation unit shall not #define or #undef names lexically identical to keywords.

[Lillehammer: Beman provided new wording]

### 295. Is abs defined in <cmath>?

Section: 26.8 [c.math] Status: CD1 Submitter: Jens Maurer Opened: 2001-01-12 Last modified: 2008-09-26

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Discussion:

Table 80 lists the contents of the <cmath> header. It does not list `abs()`. However, 26.5, paragraph 6, which lists added signatures present in <cmath>, does say that several overloads of `abs()` should be defined in <cmath>.

Proposed resolution:

Add `abs` to Table 80. Also, remove the parenthetical list of functions "(abs(), div(), rand(), srand())" from 26.6 [numarray], paragraph 1.

[Copenhagen: Modified proposed resolution so that it also gets rid of that vestigial list of functions in paragraph 1.]

Rationale:

All this DR does is fix a typo; it's uncontroversial. A separate question is whether we're doing the right thing in putting some overloads in <cmath> that we aren't also putting in <cstdlib>. That's issue 323.

### 297. const_mem_fun_t<>::argument_type should be const T*

Section: 20.7.8 [logical.operations] Status: CD1 Submitter: Martin Sebor Opened: 2001-01-06 Last modified: 2008-09-26

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Discussion:

The class templates `const_mem_fun_t` in 20.5.8, p8 and `const_mem_fun1_t` in 20.5.8, p9 derive from `unary_function<T*, S>`, and `binary_function<T*, A, S>`, respectively. Consequently, their `argument_type`, and `first_argument_type` members, respectively, are both defined to be `T*` (non-const). However, their function call member operator takes a `const T*` argument. It is my opinion that `argument_type` should be `const T*` instead, so that one can easily refer to it in generic code. The example below derived from existing code fails to compile due to the discrepancy:

`template <class T>`
`void foo (typename T::argument_type arg) // #1`
`{`
`typename T::result_type (T::*pf) (typename T::argument_type) const = // #2`
`&T::operator();`
`}`

`struct X { /* ... */ };`

`int main ()`
`{`
`const X x;`
`foo<std::const_mem_fun_t<void, X> >(&x); // #3`
`}`

#1 `foo()` takes a plain unqualified `X*` as an argument
#2 the type of the pointer is incompatible with the type of the member function
#3 the address of a constant being passed to a function taking a non-const `X*`

Proposed resolution:

Replace the top portion of the definition of the class template const_mem_fun_t in 20.5.8, p8

`template <class S, class T> class const_mem_fun_t`
`: public unary_function<T*, S> {`

with

`template <class S, class T> class const_mem_fun_t`
`: public unary_function<const T*, S> {`

Also replace the top portion of the definition of the class template const_mem_fun1_t in 20.5.8, p9

`template <class S, class T, class A> class const_mem_fun1_t`
`: public binary_function<T*, A, S> {`

with

`template <class S, class T, class A> class const_mem_fun1_t`
`: public binary_function<const T*, A, S> {`

Rationale:

This is simply a contradiction: the `argument_type` typedef, and the argument type itself, are not the same.

### 298. ::operator delete[] requirement incorrect/insufficient

Section: 18.6.1.2 [new.delete.array] Status: CD1 Submitter: John A. Pedretti Opened: 2001-01-10 Last modified: 2008-09-26

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Discussion:

The default behavior of `operator delete[]` described in 18.5.1.2, p12 - namely that for non-null value of ptr, the operator reclaims storage allocated by the earlier call to the default `operator new[]` - is not correct in all cases. Since the specified `operator new[]` default behavior is to call `operator new` (18.5.1.2, p4, p8), which can be replaced, along with `operator delete`, by the user, to implement their own memory management, the specified default behavior of`operator delete[]` must be to call `operator delete`.

Proposed resolution:

Change 18.5.1.2, p12 from

> -12- Default behavior:

> - For a null value of `ptr` , does nothing.
> - Any other value of `ptr` shall be a value returned earlier by a call to the default `operator new[](std::size_t)`. [Footnote: The value must not have been invalidated by an intervening call to `operator delete[](void*)` (17.6.3.9 [res.on.arguments]). --- end footnote] For such a non-null value of `ptr` , reclaims storage allocated by the earlier call to the default `operator new[]`.

to

> -12- Default behavior: Calls `operator delete(`ptr) or `operator delete(ptr, std::nothrow)` respectively.

and expunge paragraph 13.

### 300. list::merge() specification incomplete

Section: 23.3.4.4 [list.ops] Status: CD1 Submitter: John Pedretti Opened: 2001-01-23 Last modified: 2008-09-26

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Discussion:

The "Effects" clause for list::merge() (23.3.4.4 [list.ops], p23) appears to be incomplete: it doesn't cover the case where the argument list is identical to *this (i.e., this == &x). The requirement in the note in p24 (below) is that x be empty after the merge which is surely unintended in this case.

Proposed resolution:

In 23.3.4.4 [list.ops], replace paragraps 23-25 with:

> 23 Effects: if (&x == this) does nothing; otherwise, merges the two sorted ranges [begin(), end()) and [x.begin(), x.end()). The result is a range in which the elements will be sorted in non-decreasing order according to the ordering defined by comp; that is, for every iterator i in the range other than the first, the condition comp(*i, *(i - 1)) will be false.

> 24 Notes: Stable: if (&x != this), then for equivalent elements in the two original ranges, the elements from the original range [begin(), end()) always precede the elements from the original range [x.begin(), x.end()). If (&x != this) the range [x.begin(), x.end()) is empty after the merge.

> 25 Complexity: At most size() + x.size() - 1 applications of comp if (&x ! = this); otherwise, no applications of comp are performed. If an exception is thrown other than by a comparison there are no effects.

[Copenhagen: The original proposed resolution did not fix all of the problems in 23.3.4.4 [list.ops], p22-25. Three different paragraphs (23, 24, 25) describe the effects of `merge`. Changing p23, without changing the other two, appears to introduce contradictions. Additionally, "merges the argument list into the list" is excessively vague.]

[Post-Curaçao: Robert Klarer provided new wording.]

### 301. basic_string template ctor effects clause omits allocator argument

Section: 21.4.1 [string.require] Status: CD1 Submitter: Martin Sebor Opened: 2001-01-27 Last modified: 2008-09-26

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Discussion:

The effects clause for the basic_string template ctor in 21.3.1, p15 leaves out the third argument of type Allocator. I believe this to be a mistake.

Proposed resolution:

Replace

> -15- Effects: If `InputIterator` is an integral type, equivalent to

> > `basic_string(static_cast<size_type>(begin), static_cast<value_type>(end))`

with

> -15- Effects: If `InputIterator` is an integral type, equivalent to

> > `basic_string(static_cast<size_type>(begin), static_cast<value_type>(end), a)`

### 303. Bitset input operator underspecified

Section: 20.3.7.3 [bitset.operators] Status: CD1 Submitter: Matt Austern Opened: 2001-02-05 Last modified: 2008-09-26

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Discussion:

In 23.3.5.3, we are told that `bitset`'s input operator "Extracts up to N (single-byte) characters from is.", where is is a stream of type `basic_istream<charT, traits>`.

The standard does not say what it means to extract single byte characters from a stream whose character type, `charT`, is in general not a single-byte character type. Existing implementations differ.

A reasonable solution will probably involve `widen()` and/or `narrow()`, since they are the supplied mechanism for converting a single character between `char` and arbitrary `charT`.

Narrowing the input characters is not the same as widening the literals `'0'` and `'1'`, because there may be some locales in which more than one wide character maps to the narrow character `'0'`. Narrowing means that alternate representations may be used for bitset input, widening means that they may not be.

Note that for numeric input, `num_get<>` (22.2.2.1.2/8) compares input characters to widened version of narrow character literals.

From Pete Becker, in c++std-lib-8224:

> Different writing systems can have different representations for the digits that represent 0 and 1. For example, in the Unicode representation of the Devanagari script (used in many of the Indic languages) the digit 0 is 0x0966, and the digit 1 is 0x0967. Calling narrow would translate those into '0' and '1'. But Unicode also provides the ASCII values 0x0030 and 0x0031 for for the Latin representations of '0' and '1', as well as code points for the same numeric values in several other scripts (Tamil has no character for 0, but does have the digits 1-9), and any of these values would also be narrowed to '0' and '1'.

> ...

> It's fairly common to intermix both native and Latin representations of numbers in a document. So I think the rule has to be that if a wide character represents a digit whose value is 0 then the bit should be cleared; if it represents a digit whose value is 1 then the bit should be set; otherwise throw an exception. So in a Devanagari locale, both 0x0966 and 0x0030 would clear the bit, and both 0x0967 and 0x0031 would set it. Widen can't do that. It would pick one of those two values, and exclude the other one.

From Jens Maurer, in c++std-lib-8233:

> Whatever we decide, I would find it most surprising if bitset conversion worked differently from int conversion with regard to alternate local representations of numbers.

> Thus, I think the options are:

> - Have a new defect issue for 22.2.2.1.2/8 so that it will require the use of narrow().
> - Have a defect issue for bitset() which describes clearly that widen() is to be used.

Proposed resolution:

Replace the first two sentences of paragraph 5 with:

> Extracts up to N characters from is. Stores these characters in a temporary object str of type `basic_string<charT, traits>`, then evaluates the expression `x = bitset<N>(str)`.

Replace the third bullet item in paragraph 5 with:

- the next input character is neither `is.widen(0)` nor `is.widen(1)` (in which case the input character is not extracted).

Rationale:

Input for `bitset` should work the same way as numeric input. Using `widen` does mean that alternative digit representations will not be recognized, but this was a known consequence of the design choice.

### 305. Default behavior of codecvt<wchar_t, char, mbstate_t>::length()

Section: 22.4.1.5 [locale.codecvt.byname] Status: CD1 Submitter: Howard Hinnant Opened: 2001-01-24 Last modified: 2008-09-26

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Discussion:

22.2.1.5/3 introduces codecvt in part with:

> codecvt<wchar_t,char,mbstate_t> converts between the native character sets for tiny and wide characters. Instantiations on mbstate_t perform conversion between encodings known to the library implementor.

But 22.2.1.5.2/10 describes do_length in part with:

> ... codecvt<wchar_t, char, mbstate_t> ... return(s) the lesser of max and (from_end-from).

The semantics of do_in and do_length are linked. What one does must be consistent with what the other does. 22.2.1.5/3 leads me to believe that the vendor is allowed to choose the algorithm that codecvt<wchar_t,char,mbstate_t>::do_in performs so that it makes his customers happy on a given platform. But 22.2.1.5.2/10 explicitly says what codecvt<wchar_t,char,mbstate_t>::do_length must return. And thus indirectly specifies the algorithm that codecvt<wchar_t,char,mbstate_t>::do_in must perform. I believe that this is not what was intended and is a defect.

Discussion from the -lib reflector:
This proposal would have the effect of making the semantics of all of the virtual functions in `codecvt<wchar_t, char, mbstate_t>` implementation specified. Is that what we want, or do we want to mandate specific behavior for the base class virtuals and leave the implementation specified behavior for the codecvt_byname derived class? The tradeoff is that former allows implementors to write a base class that actually does something useful, while the latter gives users a way to get known and specified---albeit useless---behavior, and is consistent with the way the standard handles other facets. It is not clear what the original intention was.

Nathan has suggest a compromise: a character that is a widened version of the characters in the basic execution character set must be converted to a one-byte sequence, but there is no such requirement for characters that are not part of the basic execution character set.

Proposed resolution:

Change 22.2.1.5.2/5 from:

The instantiations required in Table 51 (lib.locale.category), namely codecvt<wchar_t,char,mbstate_t> and codecvt<char,char,mbstate_t>, store no characters. Stores no more than (to_limit-to) destination elements. It always leaves the to_next pointer pointing one beyond the last element successfully stored.

to:

Stores no more than (to_limit-to) destination elements, and leaves the to_next pointer pointing one beyond the last element successfully stored. codecvt<char,char,mbstate_t> stores no characters.

Change 22.2.1.5.2/10 from:

> -10- Returns: (from_next-from) where from_next is the largest value in the range [from,from_end] such that the sequence of values in the range [from,from_next) represents max or fewer valid complete characters of type internT. The instantiations required in Table 51 (21.1.1.1.1), namely codecvt<wchar_t, char, mbstate_t> and codecvt<char, char, mbstate_t>, return the lesser of max and (from_end-from).

to:

> -10- Returns: (from_next-from) where from_next is the largest value in the range [from,from_end] such that the sequence of values in the range [from,from_next) represents max or fewer valid complete characters of type internT. The instantiation codecvt<char, char, mbstate_t> returns the lesser of max and (from_end-from).

[Redmond: Nathan suggested an alternative resolution: same as above, but require that, in the default encoding, a character from the basic execution character set would map to a single external character. The straw poll was 8-1 in favor of the proposed resolution.]

Rationale:

The default encoding should be whatever users of a given platform would expect to be the most natural. This varies from platform to platform. In many cases there is a preexisting C library, and users would expect the default encoding to be whatever C uses in the default "C" locale. We could impose a guarantee like the one Nathan suggested (a character from the basic execution character set must map to a single external character), but this would rule out important encodings that are in common use: it would rule out JIS, for example, and it would rule out a fixed-width encoding of UCS-4.

[Curaçao: fixed rationale typo at the request of Ichiro Koshida; "shift-JIS" changed to "JIS".]

### 306. offsetof macro and non-POD types

Section: 18.2 [support.types] Status: CD1 Submitter: Steve Clamage Opened: 2001-02-21 Last modified: 2008-09-26

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Discussion:

Spliced together from reflector messages c++std-lib-8294 and -8295:

18.1, paragraph 5, reads: "The macro `offsetof` accepts a restricted set of type arguments in this International Standard. type shall be a POD structure or a POD union (clause 9). The result of applying the offsetof macro to a field that is a static data member or a function member is undefined."

For the POD requirement, it doesn't say "no diagnostic required" or "undefined behavior". I read 1.4 [intro.compliance], paragraph 1, to mean that a diagnostic is required. It's not clear whether this requirement was intended. While it's possible to provide such a diagnostic, the extra complication doesn't seem to add any value.

Proposed resolution:

Change 18.1, paragraph 5, to "If type is not a POD structure or a POD union the results are undefined."

[Copenhagen: straw poll was 7-4 in favor. It was generally agreed that requiring a diagnostic was inadvertent, but some LWG members thought that diagnostics should be required whenever possible.]

### 307. Lack of reference typedefs in container adaptors

Section: 23.3.4 [list] Status: CD1 Submitter: Howard Hinnant Opened: 2001-03-13 Last modified: 2008-09-26

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Discussion:

From reflector message c++std-lib-8330. See also lib-8317.

The standard is currently inconsistent in 23.3.4.2 [list.capacity] paragraph 1 and 23.3.4.3 [list.modifiers] paragraph 1. 23.2.3.3/1, for example, says:

> -1- Any sequence supporting operations back(), push_back() and pop_back() can be used to instantiate stack. In particular, vector (lib.vector), list (lib.list) and deque (lib.deque) can be used.

But this is false: vector<bool> can not be used, because the container adaptors return a T& rather than using the underlying container's reference type.

This is a contradiction that can be fixed by:

1. Modifying these paragraphs to say that vector<bool> is an exception.
2. Removing the vector<bool> specialization.
3. Changing the return types of stack and priority_queue to use reference typedef's.

I propose 3. This does not preclude option 2 if we choose to do it later (see issue 96); the issues are independent. Option 3 offers a small step towards support for proxied containers. This small step fixes a current contradiction, is easy for vendors to implement, is already implemented in at least one popular lib, and does not break any code.

Proposed resolution:

Summary: Add reference and const_reference typedefs to queue, priority_queue and stack. Change return types of "value_type&" to "reference". Change return types of "const value_type&" to "const_reference". Details:

Change 23.2.3.1/1 from:

      namespace std {
        template <class T, class Container = deque<T> >
        class queue {
        public:
          typedef typename Container::value_type            value_type;
          typedef typename Container::size_type             size_type;
          typedef          Container                        container_type;
        protected:
          Container c;

        public:
          explicit queue(const Container& = Container());

          bool      empty() const             { return c.empty(); }
          size_type size()  const             { return c.size(); }
          value_type&       front()           { return c.front(); }
          const value_type& front() const     { return c.front(); }
          value_type&       back()            { return c.back(); }
          const value_type& back() const      { return c.back(); }
          void push(const value_type& x)      { c.push_back(x); }
          void pop()                          { c.pop_front(); }
        };

to:

      namespace std {
        template <class T, class Container = deque<T> >
        class queue {
        public:
          typedef typename Container::value_type            value_type;
          typedef typename Container::reference             reference;
          typedef typename Container::const_reference       const_reference;
          typedef typename Container::value_type            value_type;
          typedef typename Container::size_type             size_type;
          typedef          Container                        container_type;
        protected:
          Container c;

        public:
          explicit queue(const Container& = Container());

          bool      empty() const             { return c.empty(); }
          size_type size()  const             { return c.size(); }
          reference         front()           { return c.front(); }
          const_reference   front() const     { return c.front(); }
          reference         back()            { return c.back(); }
          const_reference   back() const      { return c.back(); }
          void push(const value_type& x)      { c.push_back(x); }
          void pop()                          { c.pop_front(); }
        };

Change 23.2.3.2/1 from:

      namespace std {
        template <class T, class Container = vector<T>,
                  class Compare = less<typename Container::value_type> >
        class priority_queue {
        public:
          typedef typename Container::value_type            value_type;
          typedef typename Container::size_type             size_type;
          typedef          Container                        container_type;
        protected:
          Container c;
          Compare comp;

        public:
          explicit priority_queue(const Compare& x = Compare(),
                                  const Container& = Container());
          template <class InputIterator>
            priority_queue(InputIterator first, InputIterator last,
                           const Compare& x = Compare(),
                           const Container& = Container());

          bool      empty() const       { return c.empty(); }
          size_type size()  const       { return c.size(); }
          const value_type& top() const { return c.front(); }
          void push(const value_type& x);
          void pop();
        };
                                      //  no equality is provided
      }

to:

      namespace std {
        template <class T, class Container = vector<T>,
                  class Compare = less<typename Container::value_type> >
        class priority_queue {
        public:
          typedef typename Container::value_type            value_type;
          typedef typename Container::reference             reference;
          typedef typename Container::const_reference       const_reference;
          typedef typename Container::size_type             size_type;
          typedef          Container                        container_type;
        protected:
          Container c;
          Compare comp;

        public:
          explicit priority_queue(const Compare& x = Compare(),
                                  const Container& = Container());
          template <class InputIterator>
            priority_queue(InputIterator first, InputIterator last,
                           const Compare& x = Compare(),
                           const Container& = Container());

          bool      empty() const       { return c.empty(); }
          size_type size()  const       { return c.size(); }
          const_reference   top() const { return c.front(); }
          void push(const value_type& x);
          void pop();
        };
                                      //  no equality is provided
      }

And change 23.2.3.3/1 from:

      namespace std {
        template <class T, class Container = deque<T> >
        class stack {
        public:
          typedef typename Container::value_type            value_type;
          typedef typename Container::size_type             size_type;
          typedef          Container                        container_type;
        protected:
          Container c;

        public:
          explicit stack(const Container& = Container());

          bool      empty() const             { return c.empty(); }
          size_type size()  const             { return c.size(); }
          value_type&       top()             { return c.back(); }
          const value_type& top() const       { return c.back(); }
          void push(const value_type& x)      { c.push_back(x); }
          void pop()                          { c.pop_back(); }
        };

        template <class T, class Container>
          bool operator==(const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator< (const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator!=(const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator> (const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator>=(const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator<=(const stack<T, Container>& x,
                          const stack<T, Container>& y);
      }

to:

      namespace std {
        template <class T, class Container = deque<T> >
        class stack {
        public:
          typedef typename Container::value_type            value_type;
          typedef typename Container::reference             reference;
          typedef typename Container::const_reference       const_reference;
          typedef typename Container::size_type             size_type;
          typedef          Container                        container_type;
        protected:
          Container c;

        public:
          explicit stack(const Container& = Container());

          bool      empty() const             { return c.empty(); }
          size_type size()  const             { return c.size(); }
          reference         top()             { return c.back(); }
          const_reference   top() const       { return c.back(); }
          void push(const value_type& x)      { c.push_back(x); }
          void pop()                          { c.pop_back(); }
        };

        template <class T, class Container>
          bool operator==(const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator< (const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator!=(const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator> (const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator>=(const stack<T, Container>& x,
                          const stack<T, Container>& y);
        template <class T, class Container>
          bool operator<=(const stack<T, Container>& x,
                          const stack<T, Container>& y);
      }

[Copenhagen: This change was discussed before the IS was released and it was deliberately not adopted. Nevertheless, the LWG believes (straw poll: 10-2) that it is a genuine defect.]

### 308. Table 82 mentions unrelated headers

Section: 27 [input.output] Status: CD1 Submitter: Martin Sebor Opened: 2001-03-15 Last modified: 2008-09-26

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Discussion:

Table 82 in section 27 mentions the header <cstdlib> for String streams (27.8 [string.streams]) and the headers <cstdio> and <cwchar> for File streams (27.9 [file.streams]). It's not clear why these headers are mentioned in this context since they do not define any of the library entities described by the subclauses. According to 17.6.1.1 [contents], only such headers are to be listed in the summary.

Proposed resolution:

Remove <cstdlib> and <cwchar> from Table 82.

[Copenhagen: changed the proposed resolution slightly. The original proposed resolution also said to remove <cstdio> from Table 82. However, <cstdio> is mentioned several times within section 27.9 [file.streams], including 27.9.2 [c.files].]

### 310. Is errno a macro?

Section: 17.6.1.2 [headers], 19.4 [errno] Status: CD1 Submitter: Steve Clamage Opened: 2001-03-21 Last modified: 2008-09-26

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Discussion:

Exactly how should errno be declared in a conforming C++ header?

The C standard says in 7.1.4 that it is unspecified whether errno is a macro or an identifier with external linkage. In some implementations it can be either, depending on compile-time options. (E.g., on Solaris in multi-threading mode, errno is a macro that expands to a function call, but is an extern int otherwise. "Unspecified" allows such variability.)

The C++ standard:

- 17.4.1.2 says in a note that errno must be macro in C. (false)
- 17.4.3.1.3 footnote 166 says errno is reserved as an external name (true), and implies that it is an identifier.
- 19.3 simply lists errno as a macro (by what reasoning?) and goes on to say that the contents of of C++ <errno.h> are the same as in C, begging the question.
- C.2, table 95 lists errno as a macro, without comment.

I find no other references to errno.

We should either explicitly say that errno must be a macro, even though it need not be a macro in C, or else explicitly leave it unspecified. We also need to say something about namespace std. A user who includes <cerrno> needs to know whether to write `errno`, or `::errno`, or `std::errno`, or else <cerrno> is useless.

Two acceptable fixes:

- errno must be a macro. This is trivially satisfied by adding
  #define errno (::std::errno)
  to the headers if errno is not already a macro. You then always write errno without any scope qualification, and it always expands to a correct reference. Since it is always a macro, you know to avoid using errno as a local identifer.

- errno is in the global namespace. This fix is inferior, because ::errno is not guaranteed to be well-formed.

[ This issue was first raised in 1999, but it slipped through the cracks. ]

Proposed resolution:

Change the Note in section 17.4.1.2p5 from

> Note: the names defined as macros in C include the following: assert, errno, offsetof, setjmp, va_arg, va_end, and va_start.

to

> Note: the names defined as macros in C include the following: assert, offsetof, setjmp, va_arg, va_end, and va_start.

In section 19.3, change paragraph 2 from

> The contents are the same as the Standard C library header <errno.h>.

to

> The contents are the same as the Standard C library header <errno.h>, except that errno shall be defined as a macro.

Rationale:

C++ must not leave it up to the implementation to decide whether or not a name is a macro; it must explicitly specify exactly which names are required to be macros. The only one that really works is for it to be a macro.

[Curaçao: additional rationale added.]

### 311. Incorrect wording in basic_ostream class synopsis

Section: 27.7.2.1 [ostream] Status: CD1 Submitter: Andy Sawyer Opened: 2001-03-21 Last modified: 2008-09-26

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Discussion:

In 27.7.2.1 [ostream], the synopsis of class basic_ostream says:

      // partial specializationss
      template<class traits>
        basic_ostream<char,traits>& operator<<( basic_ostream<char,traits>&,
                                                const char * );

Problems:

- Too many 's's at the end of "specializationss"
- This is an overload, not a partial specialization

Proposed resolution:

In the synopsis in 27.7.2.1 [ostream], remove the // partial specializationss comment. Also remove the same comment (correctly spelled, but still incorrect) from the synopsis in 27.7.2.6.4 [ostream.inserters.character].

[ Pre-Redmond: added 27.7.2.6.4 [ostream.inserters.character] because of Martin's comment in c++std-lib-8939. ]

### 312. Table 27 is missing headers

Section: 20 [utilities] Status: CD1 Submitter: Martin Sebor Opened: 2001-03-29 Last modified: 2008-09-26

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Discussion:

Table 27 in section 20 lists the header <memory> (only) for Memory (lib.memory) but neglects to mention the headers <cstdlib> and <cstring> that are discussed in 20.6.5 [meta.rel].

Proposed resolution:

Add <cstdlib> and <cstring> to Table 27, in the same row as <memory>.

### 315. Bad "range" in list::unique complexity

Section: 23.3.4.4 [list.ops] Status: CD1 Submitter: Andy Sawyer Opened: 2001-05-01 Last modified: 2008-09-26

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Discussion:

23.3.4.4 [list.ops], Para 21 describes the complexity of list::unique as: "If the range (last - first) is not empty, exactly (last - first) -1 applications of the corresponding predicate, otherwise no applications of the predicate)".

"(last - first)" is not a range.

Proposed resolution:

Change the "range" from (last - first) to [first, last).

### 316. Vague text in Table 69

Section: 23.2.4 [associative.reqmts] Status: CD1 Submitter: Martin Sebor Opened: 2001-05-04 Last modified: 2008-09-26

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Discussion:

Table 69 says this about a_uniq.insert(t):

> inserts t if and only if there is no element in the container with key equivalent to the key of t. The bool component of the returned pair indicates whether the insertion takes place and the iterator component of the pair points to the element with key equivalent to the key of t.

The description should be more specific about exactly how the bool component indicates whether the insertion takes place.

Proposed resolution:

Change the text in question to

> ...The bool component of the returned pair is true if and only if the insertion takes place...

### 317. Instantiation vs. specialization of facets

Section: 22 [localization] Status: CD1 Submitter: Martin Sebor Opened: 2001-05-04 Last modified: 2008-09-26

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Discussion:

The localization section of the standard refers to specializations of the facet templates as instantiations even though the required facets are typically specialized rather than explicitly (or implicitly) instantiated. In the case of ctype<char> and ctype_byname<char> (and the wchar_t versions), these facets are actually required to be specialized. The terminology should be corrected to make it clear that the standard doesn't mandate explicit instantiation (the term specialization encompasses both explicit instantiations and specializations).

Proposed resolution:

In the following paragraphs, replace all occurrences of the word instantiation or instantiations with specialization or specializations, respectively:

> 22.1.1.1.1, p4, Table 52, 22.2.1.1, p2, 22.2.1.5, p3, 22.2.1.5.1, p5, 22.2.1.5.2, p10, 22.2.2, p2, 22.2.3.1, p1, 22.2.3.1.2, p1, p2 and p3, 22.2.4.1, p1, 22.2.4.1.2, p1, 22,2,5, p1, 22,2,6, p2, 22.2.6.3.2, p7, and Footnote 242.

And change the text in 22.1.1.1.1, p4 from

> An implementation is required to provide those instantiations for facet templates identified as members of a category, and for those shown in Table 52:

to

> An implementation is required to provide those specializations...

[Nathan will review these changes, and will look for places where explicit specialization is necessary.]

Rationale:

This is a simple matter of outdated language. The language to describe templates was clarified during the standardization process, but the wording in clause 22 was never updated to reflect that change.

### 318. Misleading comment in definition of numpunct_byname

Section: 22.4.3.2 [locale.numpunct.byname] Status: CD1 Submitter: Martin Sebor Opened: 2001-05-12 Last modified: 2008-09-26

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Discussion:

The definition of the numpunct_byname template contains the following comment:

        namespace std {
            template <class charT>
            class numpunct_byname : public numpunct<charT> {
        // this class is specialized for char and wchar_t.
            ...

There is no documentation of the specializations and it seems conceivable that an implementation will not explicitly specialize the template at all, but simply provide the primary template.

Proposed resolution:

Remove the comment from the text in 22.2.3.2 and from the proposed resolution of library issue 228.

### 319. Storage allocation wording confuses "Required behavior", "Requires"

Section: 18.6.1.1 [new.delete.single], 18.6.1.2 [new.delete.array] Status: CD1 Submitter: Beman Dawes Opened: 2001-05-15 Last modified: 2008-09-26

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Discussion:

The standard specifies 17.5.1.4 [structure.specifications] that "Required behavior" elements describe "the semantics of a function definition provided by either the implementation or a C++ program."

The standard specifies 17.5.1.4 [structure.specifications] that "Requires" elements describe "the preconditions for calling the function."

In the sections noted below, the current wording specifies "Required Behavior" for what are actually preconditions, and thus should be specified as "Requires".

Proposed resolution:

In 18.6.1.1 [new.delete.single] Para 12 Change:

> Required behavior: accept a value of ptr that is null or that was returned by an earlier call ...

to:

> Requires: the value of ptr is null or the value returned by an earlier call ...

In 18.6.1.2 [new.delete.array] Para 11 Change:

> Required behavior: accept a value of ptr that is null or that was returned by an earlier call ...

to:

> Requires: the value of ptr is null or the value returned by an earlier call ...

### 320. list::assign overspecified

Section: 23.3.4.1 [list.cons] Status: CD1 Submitter: Howard Hinnant Opened: 2001-05-17 Last modified: 2008-09-26

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Discussion:

Section 23.3.4.1 [list.cons], paragraphs 6-8 specify that list assign (both forms) have the "effects" of a call to erase followed by a call to insert.

I would like to document that implementers have the freedom to implement assign by other methods, as long as the end result is the same and the exception guarantee is as good or better than the basic guarantee.

The motivation for this is to use T's assignment operator to recycle existing nodes in the list instead of erasing them and reallocating them with new values. It is also worth noting that, with careful coding, most common cases of assign (everything but assignment with true input iterators) can elevate the exception safety to strong if T's assignment has a nothrow guarantee (with no extra memory cost). Metrowerks does this. However I do not propose that this subtlety be standardized. It is a QoI issue.

Existing practise: Metrowerks and SGI recycle nodes, Dinkumware and Rogue Wave don't.

Proposed resolution:

Change 23.3.4.1 [list.cons]/7 from:

> Effects:

>        erase(begin(), end());
>        insert(begin(), first, last);

to:

> Effects: Replaces the contents of the list with the range [first, last).

In 23.2.3 [sequence.reqmts], in Table 67 (sequence requirements), add two new rows:

          a.assign(i,j)     void      pre: i,j are not iterators into a.
                                      Replaces elements in a with a copy
                                      of [i, j).

          a.assign(n,t)     void      pre: t is not a reference into a.
                                      Replaces elements in a with n copies
                                      of t.

Change 23.3.4.1 [list.cons]/8 from:

> Effects:

>        erase(begin(), end());
>        insert(begin(), n, t);

to:

> Effects: Replaces the contents of the list with n copies of t.

[Redmond: Proposed resolution was changed slightly. Previous version made explicit statement about exception safety, which wasn't consistent with the way exception safety is expressed elsewhere. Also, the change in the sequence requirements is new. Without that change, the proposed resolution would have required that assignment of a subrange would have to work. That too would have been overspecification; it would effectively mandate that assignment use a temporary. Howard provided wording. ]

[Curaçao: Made editorial improvement in wording; changed "Replaces elements in a with copies of elements in [i, j)." with "Replaces the elements of a with a copy of [i, j)." Changes not deemed serious enough to requre rereview.]

### 321. Typo in num_get

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 Submitter: Kevin Djang Opened: 2001-05-17 Last modified: 2008-09-26

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Discussion:

Section 22.2.2.1.2 at p7 states that "A length specifier is added to the conversion function, if needed, as indicated in Table 56." However, Table 56 uses the term "length modifier", not "length specifier".

Proposed resolution:

In 22.2.2.1.2 at p7, change the text "A length specifier is added ..." to be "A length modifier is added ..."

Rationale:

C uses the term "length modifier". We should be consistent.

### 322. iterator and const_iterator should have the same value type

Section: 23.2 [container.requirements] Status: CD1 Submitter: Matt Austern Opened: 2001-05-17 Last modified: 2008-09-26

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Discussion:

It's widely assumed that, if X is a container, iterator_traits<X::iterator>::value_type and iterator_traits<X::const_iterator>::value_type should both be X::value_type. However, this is nowhere stated. The language in Table 65 is not precise about the iterators' value types (it predates iterator_traits), and could even be interpreted as saying that iterator_traits<X::const_iterator>::value_type should be "const X::value_type".

Related issue: 279.

Proposed resolution:

In Table 65 ("Container Requirements"), change the return type for X::iterator to "iterator type whose value type is T". Change the return type for X::const_iterator to "constant iterator type whose value type is T".

Rationale:

This belongs as a container requirement, rather than an iterator requirement, because the whole notion of iterator/const_iterator pairs is specific to containers' iterator.

It is existing practice that (for example) iterator_traits<list<int>::const_iterator>::value_type is "int", rather than "const int". This is consistent with the way that const pointers are handled: the standard already requires that iterator_traits<const int*>::value_type is int.

### 324. Do output iterators have value types?

Section: 24.2.2 [output.iterators] Status: CD1 Submitter: Dave Abrahams Opened: 2001-06-07 Last modified: 2008-09-26

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Discussion:

Table 73 suggests that output iterators have value types. It requires the expression "*a = t". Additionally, although Table 73 never lists "a = t" or "X(a) = t" in the "expressions" column, it contains a note saying that "a = t" and "X(a) = t" have equivalent (but nowhere specified!) semantics.

According to 24.1/9, t is supposed to be "a value of value type T":

> In the following sections, a and b denote values of X, n denotes a value of the difference type Distance, u, tmp, and m denote identifiers, r denotes a value of X&, t denotes a value of value type T.

Two other parts of the standard that are relevant to whether output iterators have value types:

- 24.1/1 says "All iterators i support the expression *i, resulting in a value of some class, enumeration, or built-in type T, called the value type of the iterator".
- 24.3.1/1, which says "In the case of an output iterator, the types iterator_traits<Iterator>::difference_type iterator_traits<Iterator>::value_type are both defined as void."

The first of these passages suggests that "*i" is supposed to return a useful value, which contradicts the note in 24.1.2/2 saying that the only valid use of "*i" for output iterators is in an expression of the form "*i = t". The second of these passages appears to contradict Table 73, because it suggests that "*i"'s return value should be void. The second passage is also broken in the case of a an iterator type, like non-const pointers, that satisfies both the output iterator requirements and the forward iterator requirements.

What should the standard say about `*i`'s return value when i is an output iterator, and what should it say about that t is in the expression "*i = t"? Finally, should the standard say anything about output iterators' pointer and reference types?

Proposed resolution:

24.1 p1, change

> All iterators `i` support the expression `*i`, resulting in a value of some class, enumeration, or built-in type `T`, called the value type of the iterator.

to

> All input iterators `i` support the expression `*i`, resulting in a value of some class, enumeration, or built-in type `T`, called the value type of the iterator. All output iterators support the expression `*i = o` where `o` is a value of some type that is in the set of types that are writable to the particular iterator type of `i`.

24.1 p9, add

> `o` denotes a value of some type that is writable to the output iterator.

Table 73, change

>     *a = t

to

>     *r = o

and change

>     *r++ = t

to

>     *r++ = o

[post-Redmond: Jeremy provided wording]

Rationale:

The LWG considered two options: change all of the language that seems to imply that output iterators have value types, thus making it clear that output iterators have no value types, or else define value types for output iterator consistently. The LWG chose the former option, because it seems clear that output iterators were never intended to have value types. This was a deliberate design decision, and any language suggesting otherwise is simply a mistake.

A future revision of the standard may wish to revisit this design decision.

### 325. Misleading text in moneypunct<>::do_grouping

Section: 22.4.6.3.2 [locale.moneypunct.virtuals] Status: CD1 Submitter: Martin Sebor Opened: 2001-07-02 Last modified: 2008-09-26

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Discussion:

The Returns clause in 22.2.6.3.2, p3 says about moneypunct<charT>::do_grouping()

> Returns: A pattern defined identically as the result of numpunct<charT>::do_grouping().241)

Footnote 241 then reads

> This is most commonly the value "\003" (not "3").

The returns clause seems to imply that the two member functions must return an identical value which in reality may or may not be true, since the facets are usually implemented in terms of struct std::lconv and return the value of the grouping and mon_grouping, respectively. The footnote also implies that the member function of the moneypunct facet (rather than the overridden virtual functions in moneypunct_byname) most commonly return "\003", which contradicts the C standard which specifies the value of "" for the (most common) C locale.

Proposed resolution:

Replace the text in Returns clause in 22.2.6.3.2, p3 with the following:

> Returns: A pattern defined identically as, but not necessarily equal to, the result of numpunct<charT>::do_grouping().241)

and replace the text in Footnote 241 with the following:

> To specify grouping by 3s the value is "\003", not "3".

Rationale:

The fundamental problem is that the description of the locale facet virtuals serves two purposes: describing the behavior of the base class, and describing the meaning of and constraints on the behavior in arbitrary derived classes. The new wording makes that separation a little bit clearer. The footnote (which is nonnormative) is not supposed to say what the grouping is in the "C" locale or in any other locale. It is just a reminder that the values are interpreted as small integers, not ASCII characters.

### 327. Typo in time_get facet in table 52

Section: 22.3.1.1.1 [locale.category] Status: CD1 Submitter: Tiki Wan Opened: 2001-07-06 Last modified: 2008-09-26

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Duplicate of: 447

Discussion:

The `wchar_t` versions of `time_get` and `time_get_byname` are listed incorrectly in table 52, required instantiations. In both cases the second template parameter is given as OutputIterator. It should instead be InputIterator, since these are input facets.

Proposed resolution:

In table 52, required instantiations, in 22.3.1.1.1 [locale.category], change

        time_get<wchar_t, OutputIterator>
        time_get_byname<wchar_t, OutputIterator>

to

        time_get<wchar_t, InputIterator>
        time_get_byname<wchar_t, InputIterator>

[Redmond: Very minor change in proposed resolution. Original had a typo, wchart instead of wchar_t.]

### 328. Bad sprintf format modifier in money_put<>::do_put()

Section: 22.4.6.2.2 [locale.money.put.virtuals] Status: CD1 Submitter: Martin Sebor Opened: 2001-07-07 Last modified: 2008-09-26

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Discussion:

The sprintf format string , "%.01f" (that's the digit one), in the description of the do_put() member functions of the money_put facet in 22.2.6.2.2, p1 is incorrect. First, the f format specifier is wrong for values of type long double, and second, the precision of 01 doesn't seem to make sense. What was most likely intended was "%.0Lf"., that is a precision of zero followed by the L length modifier.

Proposed resolution:

Change the format string to "%.0Lf".

Rationale:

Fixes an obvious typo

### 329. vector capacity, reserve and reallocation

Section: 23.3.6.2 [vector.capacity], 23.3.6.4 [vector.modifiers] Status: CD1 Submitter: Anthony Williams Opened: 2001-07-13 Last modified: 2008-09-26

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Discussion:

There is an apparent contradiction about which circumstances can cause a reallocation of a vector in Section 23.3.6.2 [vector.capacity] and section 23.3.6.4 [vector.modifiers].

23.3.6.2 [vector.capacity],p5 says:

> Notes: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence. It is guaranteed that no reallocation takes place during insertions that happen after a call to reserve() until the time when an insertion would make the size of the vector greater than the size specified in the most recent call to reserve().

Which implies if I do

      std::vector<int> vec;
      vec.reserve(23);
      vec.reserve(0);
      vec.insert(vec.end(),1);

then the implementation may reallocate the vector for the insert, as the size specified in the previous call to reserve was zero.

However, the previous paragraphs (23.3.6.2 [vector.capacity], p1-2) state:

> (capacity) Returns: The total number of elements the vector can hold without requiring reallocation

> ...After reserve(), capacity() is greater or equal to the argument of reserve if reallocation happens; and equal to the previous value of capacity() otherwise...

This implies that vec.capacity() is still 23, and so the insert() should not require a reallocation, as vec.size() is 0. This is backed up by 23.3.6.4 [vector.modifiers], p1:

> (insert) Notes: Causes reallocation if the new size is greater than the old capacity.

Though this doesn't rule out reallocation if the new size is less than the old capacity, I think the intent is clear.

Proposed resolution:

Change the wording of 23.3.6.2 [vector.capacity] paragraph 5 to:

> Notes: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence. It is guaranteed that no reallocation takes place during insertions that happen after a call to reserve() until the time when an insertion would make the size of the vector greater than the value of capacity().

[Redmond: original proposed resolution was modified slightly. In the original, the guarantee was that there would be no reallocation until the size would be greater than the value of capacity() after the most recent call to reserve(). The LWG did not believe that the "after the most recent call to reserve()" added any useful information.]

Rationale:

There was general agreement that, when reserve() is called twice in succession and the argument to the second invocation is smaller than the argument to the first, the intent was for the second invocation to have no effect. Wording implying that such cases have an effect on reallocation guarantees was inadvertant.

### 331. bad declaration of destructor for ios_base::failure

Section: 27.5.2.1.1 [ios::failure] Status: CD1 Submitter: PremAnand M. Rao Opened: 2001-08-23 Last modified: 2008-09-26

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Discussion:

With the change in 17.6.4.11 [res.on.exception.handling] to state "An implementation may strengthen the exception-specification for a non-virtual function by removing listed exceptions." (issue 119) and the following declaration of ~failure() in ios_base::failure

        namespace std {
           class ios_base::failure : public exception {
           public:
               ...
               virtual ~failure();
               ...
           };
         }

the class failure cannot be implemented since in 18.7.1 [type.info] the destructor of class exception has an empty exception specification:

        namespace std {
           class exception {
           public:
             ...
             virtual ~exception() throw();
             ...
           };
         }

Proposed resolution:

Remove the declaration of ~failure().

Rationale:

The proposed resolution is consistent with the way that destructors of other classes derived from `exception` are handled.

### 333. does endl imply synchronization with the device?

Section: 27.7.2.8 [ostream.manip] Status: CD1 Submitter: PremAnand M. Rao Opened: 2001-08-27 Last modified: 2008-09-26

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Discussion:

A footnote in 27.7.2.8 [ostream.manip] states:

> [Footnote: The effect of executing cout << endl is to insert a newline character in the output sequence controlled by cout, then synchronize it with any external file with which it might be associated. --- end foonote]

Does the term "file" here refer to the external device? This leads to some implementation ambiguity on systems with fully buffered files where a newline does not cause a flush to the device.

Choosing to sync with the device leads to significant performance penalties for each call to endl, while not sync-ing leads to errors under special circumstances.

I could not find any other statement that explicitly defined the behavior one way or the other.

Proposed resolution:

Remove footnote 300 from section 27.7.2.8 [ostream.manip].

Rationale:

We already have normative text saying what `endl` does: it inserts a newline character and calls `flush`. This footnote is at best redundant, at worst (as this issue says) misleading, because it appears to make promises about what `flush` does.

### 334. map::operator[] specification forces inefficient implementation

Section: 23.4.1.2 [map.access] Status: CD1 Submitter: Andrea Griffini Opened: 2001-09-02 Last modified: 2008-09-26

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Discussion:

The current standard describes map::operator[] using a code example. That code example is however quite inefficient because it requires several useless copies of both the passed key_type value and of default constructed mapped_type instances. My opinion is that was not meant by the comitee to require all those temporary copies.

Currently map::operator[] behaviour is specified as:

      Returns:
        (*((insert(make_pair(x, T()))).first)).second.

This specification however uses make_pair that is a template function of which parameters in this case will be deduced being of type const key_type& and const T&. This will create a pair<key_type,T> that isn't the correct type expected by map::insert so another copy will be required using the template conversion constructor available in pair to build the required pair<const key_type,T> instance.

If we consider calling of key_type copy constructor and mapped_type default constructor and copy constructor as observable behaviour (as I think we should) then the standard is in this place requiring two copies of a key_type element plus a default construction and two copy construction of a mapped_type (supposing the addressed element is already present in the map; otherwise at least another copy construction for each type).

A simple (half) solution would be replacing the description with:

      Returns:
        (*((insert(value_type(x, T()))).first)).second.

This will remove the wrong typed pair construction that requires one extra copy of both key and value.

However still the using of map::insert requires temporary objects while the operation, from a logical point of view, doesn't require any.

I think that a better solution would be leaving free an implementer to use a different approach than map::insert that, because of its interface, forces default constructed temporaries and copies in this case. The best solution in my opinion would be just requiring map::operator[] to return a reference to the mapped_type part of the contained element creating a default element with the specified key if no such an element is already present in the container. Also a logarithmic complexity requirement should be specified for the operation.

This would allow library implementers to write alternative implementations not using map::insert and reaching optimal performance in both cases of the addressed element being present or absent from the map (no temporaries at all and just the creation of a new pair inside the container if the element isn't present). Some implementer has already taken this option but I think that the current wording of the standard rules that as non-conforming.

Proposed resolution:

Replace 23.4.1.2 [map.access] paragraph 1 with

> -1- Effects: If there is no key equivalent to x in the map, inserts value_type(x, T()) into the map.

> -2- Returns: A reference to the mapped_type corresponding to x in *this.

> -3- Complexity: logarithmic.

[This is the second option mentioned above. Howard provided wording. We may also wish to have a blanket statement somewhere in clause 17 saying that we do not intend the semantics of sample code fragments to be interpreted as specifing exactly how many copies are made. See issue 98 for a similar problem.]

Rationale:

This is the second solution described above; as noted, it is consistent with existing practice.

Note that we now need to specify the complexity explicitly, because we are no longer defining `operator[]` in terms of `insert`.

### 335. minor issue with char_traits, table 37

Section: 21.2.1 [char.traits.require] Status: CD1 Submitter: Andy Sawyer Opened: 2001-09-06 Last modified: 2008-09-26

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Discussion:

Table 37, in 21.2.1 [char.traits.require], descibes char_traits::assign as:

      X::assign(c,d)   assigns c = d.

And para 1 says:

> [...] c and d denote values of type CharT [...]

Naturally, if c and d are values, then the assignment is (effectively) meaningless. It's clearly intended that (in the case of assign, at least), 'c' is intended to be a reference type.

I did a quick survey of the four implementations I happened to have lying around, and sure enough they all have signatures:

        assign( charT&, const charT& );

(or the equivalent). It's also described this way in Nico's book. (Not to mention the synopses of char_traits<char> in 21.1.3.1 and char_traits<wchar_t> in 21.1.3.2...)

Proposed resolution:

Add the following to 21.1.1 para 1:

> r denotes an lvalue of CharT

and change the description of assign in the table to:

      X::assign(r,d)   assigns r = d

### 336. Clause 17 lack of references to deprecated headers

Section: 17 [library] Status: CD1 Submitter: Detlef Vollmann Opened: 2001-09-05 Last modified: 2008-09-26

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Discussion:

From c++std-edit-873:

17.6.1.2 [headers], Table 11. In this table, the header <strstream> is missing.

This shows a general problem: The whole clause 17 refers quite often to clauses 18 through 27, but D.7 is also a part of the standard library (though a deprecated one).

Proposed resolution:

To 17.6.1.2 [headers] Table 11, C++ Library Headers, add "<strstream>".

In the following places, change "clauses 17 through 27" to "clauses 17 through 27 and Annex D":

- 1.2 [intro.refs] Normative references/1/footnote 1
- 1.3 [intro.defs] Definitions/1
- 7 [dcl.dcl] Library introduction/9
- 17.5 [description] Method of description (Informative)/1
- 17.5.2.1.4 [character.seq] Character sequences/1/bullet 2
- 17.5.2.2 [functions.within.classes] Functions within classes/1
- 17.5.2.3 [objects.within.classes] Private members/1/(2 places)
- 17.6 [requirements] Library-wide requirements/1
- 17.6.1.2 [headers] Headers/4
- 17.6.3.6 [replacement.functions] Replacement functions/1
- 17.6.4.4 [global.functions] Global or non-member functions/2
- 17.6.4.9 [protection.within.classes] Protection within classes/1

### 337. replace_copy_if's template parameter should be InputIterator

Section: 25.3.5 [alg.replace] Status: CD1 Submitter: Detlef Vollmann Opened: 2001-09-07 Last modified: 2008-09-26

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Discussion:

From c++std-edit-876:

In section 25.3.5 [alg.replace] before p4: The name of the first parameter of template replace_copy_if should be "InputIterator" instead of "Iterator". According to 17.5.2.1 [type.descriptions] p1 the parameter name conveys real normative meaning.

Proposed resolution:

Change `Iterator` to `InputIterator`.

### 338. is whitespace allowed between `-' and a digit?

Section: 22.4 [locale.categories] Status: CD1 Submitter: Martin Sebor Opened: 2001-09-17 Last modified: 2008-09-26

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Discussion:

From Stage 2 processing in 22.4.2.1.2 [facet.num.get.virtuals], p8 and 9 (the original text or the text corrected by the proposed resolution of issue 221) it seems clear that no whitespace is allowed within a number, but 22.4.3.1 [locale.numpunct], p2, which gives the format for integer and floating point values, says that whitespace is optional between a plusminus and a sign.

The text needs to be clarified to either consistently allow or disallow whitespace between a plusminus and a sign. It might be worthwhile to consider the fact that the C library stdio facility does not permit whitespace embedded in numbers and neither does the C or C++ core language (the syntax of integer-literals is given in 2.14.2 [lex.icon], that of floating-point-literals in 2.14.4 [lex.fcon] of the C++ standard).

Proposed resolution:

Change the first part of 22.4.3.1 [locale.numpunct] paragraph 2 from:

> The syntax for number formats is as follows, where `digit` represents the radix set specified by the `fmtflags` argument value, `whitespace` is as determined by the facet `ctype<charT>` (22.2.1.1), and `thousands-sep` and `decimal-point` are the results of corresponding `numpunct<charT>` members. Integer values have the format:

>       integer   ::= [sign] units
>       sign      ::= plusminus [whitespace]
>       plusminus ::= '+' | '-'
>       units     ::= digits [thousands-sep units]
>       digits    ::= digit [digits]

to:

> The syntax for number formats is as follows, where `digit` represents the radix set specified by the `fmtflags` argument value, and `thousands-sep` and `decimal-point` are the results of corresponding `numpunct<charT>` members. Integer values have the format:

>       integer   ::= [sign] units
>       sign      ::= plusminus
>       plusminus ::= '+' | '-'
>       units     ::= digits [thousands-sep units]
>       digits    ::= digit [digits]

Rationale:

It's not clear whether the format described in 22.4.3.1 [locale.numpunct] paragraph 2 has any normative weight: nothing in the standard says how, or whether, it's used. However, there's no reason for it to differ gratuitously from the very specific description of numeric processing in 22.4.2.1.2 [facet.num.get.virtuals]. The proposed resolution removes all mention of "whitespace" from that format.

### 339. definition of bitmask type restricted to clause 27

Section: 22.4.1 [category.ctype], 17.5.2.1.3 [bitmask.types] Status: CD1 Submitter: Martin Sebor Opened: 2001-09-17 Last modified: 2008-09-26

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Discussion:

The ctype_category::mask type is declared to be an enum in 22.4.1 [category.ctype] with p1 then stating that it is a bitmask type, most likely referring to the definition of bitmask type in 17.5.2.1.3 [bitmask.types], p1. However, the said definition only applies to clause 27, making the reference in 22.2.1 somewhat dubious.

Proposed resolution:

Clarify 17.3.2.1.2, p1 by changing the current text from

> Several types defined in clause 27 are bitmask types. Each bitmask type can be implemented as an enumerated type that overloads certain operators, as an integer type, or as a bitset (20.3.7 [template.bitset]).

to read

> Several types defined in clauses lib.language.support through lib.input.output and Annex D are bitmask types. Each bitmask type can be implemented as an enumerated type that overloads certain operators, as an integer type, or as a bitset (lib.template.bitset).

Additionally, change the definition in 22.2.1 to adopt the same convention as in clause 27 by replacing the existing text with the following (note, in particluar, the cross-reference to 17.3.2.1.2 in 22.2.1, p1):

> 22.2.1 The ctype category [lib.category.ctype]

>     namespace std {
>         class ctype_base {
>         public:
>             typedef T mask;

>             // numeric values are for exposition only.
>             static const mask space = 1 << 0;
>             static const mask print = 1 << 1;
>             static const mask cntrl = 1 << 2;
>             static const mask upper = 1 << 3;
>             static const mask lower = 1 << 4;
>             static const mask alpha = 1 << 5;
>             static const mask digit = 1 << 6;
>             static const mask punct = 1 << 7;
>             static const mask xdigit = 1 << 8;
>             static const mask alnum = alpha | digit;
>             static const mask graph = alnum | punct;
>         };
>     }

> The type `mask` is a bitmask type (17.5.2.1.3 [bitmask.types]).

[Curaçao: The LWG notes that T above should be bold-italics to be consistent with the rest of the standard.]

### 340. interpretation of `has_facet<Facet>(loc)`

Section: 22.3.1.1.1 [locale.category] Status: CD1 Submitter: Martin Sebor Opened: 2001-09-18 Last modified: 2008-09-26

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Discussion:

It's unclear whether 22.1.1.1.1, p3 says that `has_facet<Facet>(loc)` returns true for any `Facet` from Table 51 or whether it includes Table 52 as well:

> For any locale `loc` either constructed, or returned by locale::classic(), and any facet `Facet` that is a member of a standard category, `has_facet<Facet>(loc)` is true. Each locale member function which takes a `locale::category` argument operates on the corresponding set of facets.

It seems that it comes down to which facets are considered to be members of a standard category. Intuitively, I would classify all the facets in Table 52 as members of their respective standard categories, but there are an unbounded set of them...

The paragraph implies that, for instance, `has_facet<num_put<C, OutputIterator> >(loc)` must always return true. I don't think that's possible. If it were, then `use_facet<num_put<C, OutputIterator> >(loc)` would have to return a reference to a distinct object for each valid specialization of `num_put<C, OutputIteratory>`, which is clearly impossible.

On the other hand, if none of the facets in Table 52 is a member of a standard category then none of the locale member functions that operate on entire categories of facets will work properly.

It seems that what p3 should mention that it's required (permitted?) to hold only for specializations of `Facet` from Table 52 on `C` from the set { `char`, `wchar_t` }, and `InputIterator` and `OutputIterator` from the set of { {i,o}`streambuf_iterator`<{`char`,`wchar_t`}`>` }.

Proposed resolution:

In 22.3.1.1.1 [locale.category], paragraph 3, change "that is a member of a standard category" to "shown in Table 51".

Rationale:

The facets in Table 52 are an unbounded set. Locales should not be required to contain an infinite number of facets.

It's not necessary to talk about which values of InputIterator and OutputIterator must be supported. Table 51 already contains a complete list of the ones we need.

### 341. Vector reallocation and swap

Section: 23.3.6.2 [vector.capacity] Status: CD1 Submitter: Anthony Williams Opened: 2001-09-27 Last modified: 2008-09-26

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Discussion:

It is a common idiom to reduce the capacity of a vector by swapping it with an empty one:

      std::vector<SomeType> vec;
      // fill vec with data
      std::vector<SomeType>().swap(vec);
      // vec is now empty, with minimal capacity

However, the wording of 23.3.6.2 [vector.capacity]paragraph 5 prevents the capacity of a vector being reduced, following a call to reserve(). This invalidates the idiom, as swap() is thus prevented from reducing the capacity. The proposed wording for issue 329 does not affect this. Consequently, the example above requires the temporary to be expanded to cater for the contents of vec, and the contents be copied across. This is a linear-time operation.

However, the container requirements state that swap must have constant complexity (23.2 [container.requirements] note to table 65).

This is an important issue, as reallocation affects the validity of references and iterators.

If the wording of 23.2.4.2p5 is taken to be the desired intent, then references and iterators remain valid after a call to swap, if they refer to an element before the new end() of the vector into which they originally pointed, in which case they refer to the element at the same index position. Iterators and references that referred to an element whose index position was beyond the new end of the vector are invalidated.

If the note to table 65 is taken as the desired intent, then there are two possibilities with regard to iterators and references:

1. All Iterators and references into both vectors are invalidated.
2. Iterators and references into either vector remain valid, and remain pointing to the same element. Consequently iterators and references that referred to one vector now refer to the other, and vice-versa.

Proposed resolution:

Add a new paragraph after 23.3.6.2 [vector.capacity] paragraph 5:

>       void swap(vector<T,Allocator>& x);

> Effects: Exchanges the contents and capacity() of `*this` with that of `x`.

> Complexity: Constant time.

[This solves the problem reported for this issue. We may also have a problem with a circular definition of swap() for other containers.]

Rationale:

swap should be constant time. The clear intent is that it should just do pointer twiddling, and that it should exchange all properties of the two vectors, including their reallocation guarantees.

### 345. type tm in <cwchar>

Section: 21.6 [c.strings] Status: CD1 Submitter: Clark Nelson Opened: 2001-10-19 Last modified: 2008-09-26

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Discussion:

C99, and presumably amendment 1 to C90, specify that <wchar.h> declares struct tm as an incomplete type. However, table 48 in 21.6 [c.strings] does not mention the type tm as being declared in <cwchar>. Is this omission intentional or accidental?

Proposed resolution:

In section 21.6 [c.strings], add "tm" to table 48.

### 346. Some iterator member functions should be const

Section: X [iterator.concepts] Status: CD1 Submitter: Jeremy Siek Opened: 2001-10-20 Last modified: 2008-09-30

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Discussion:

Iterator member functions and operators that do not change the state of the iterator should be defined as const member functions or as functions that take iterators either by const reference or by value. The standard does not explicitly state which functions should be const. Since this a fairly common mistake, the following changes are suggested to make this explicit.

The tables almost indicate constness properly through naming: r for non-const and a,b for const iterators. The following changes make this more explicit and also fix a couple problems.

Proposed resolution:

In X [iterator.concepts] Change the first section of p9 from "In the following sections, a and b denote values of X..." to "In the following sections, a and b denote values of type const X...".

In Table 73, change

        a->m   U&         ...

to

        a->m   const U&   ...
        r->m   U&         ...

In Table 73 expression column, change

        *a = t

to

        *r = t

[Redmond: The container requirements should be reviewed to see if the same problem appears there.]

### 347. locale::category and bitmask requirements

Section: 22.3.1.1.1 [locale.category] Status: CD1 Submitter: P.J. Plauger, Nathan Myers Opened: 2001-10-23 Last modified: 2008-09-26

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Discussion:

In 22.3.1.1.1 [locale.category] paragraph 1, the category members are described as bitmask elements. In fact, the bitmask requirements in 17.5.2.1.3 [bitmask.types] don't seem quite right: `none` and `all` are bitmask constants, not bitmask elements.

In particular, the requirements for `none` interact poorly with the requirement that the LC_* constants from the C library must be recognizable as C++ locale category constants. LC_* values should not be mixed with these values to make category values.

We have two options for the proposed resolution. Informally: option 1 removes the requirement that LC_* values be recognized as category arguments. Option 2 changes the category type so that this requirement is implementable, by allowing `none` to be some value such as 0x1000 instead of 0.

Nathan writes: "I believe my proposed resolution [Option 2] merely re-expresses the status quo more clearly, without introducing any changes beyond resolving the DR.

Proposed resolution:

Replace the first two paragraphs of 22.3.1.1 [locale.types] with:

>         typedef int category;

> Valid category values include the `locale` member bitmask elements `collate`, `ctype`, `monetary`, `numeric`, `time`, and `messages`, each of which represents a single locale category. In addition, `locale` member bitmask constant `none` is defined as zero and represents no category. And locale member bitmask constant `all` is defined such that the expression

>         (collate | ctype | monetary | numeric | time | messages | all) == all

> is `true`, and represents the union of all categories. Further the expression `(X | Y)`, where `X` and `Y` each represent a single category, represents the union of the two categories.

> `locale` member functions expecting a `category` argument require one of the `category` values defined above, or the union of two or more such values. Such a `category` argument identifies a set of locale categories. Each locale category, in turn, identifies a set of locale facets, including at least those shown in Table 51:

[Curaçao: need input from locale experts.]

Rationale:

The LWG considered, and rejected, an alternate proposal (described as "Option 2" in the discussion). The main reason for rejecting it was that library implementors were concerened about implementation difficult, given that getting a C++ library to work smoothly with a separately written C library is already a delicate business. Some library implementers were also concerned about the issue of adding extra locale categories.

> Option 2:
> Replace the first paragraph of 22.3.1.1 [locale.types] with:

> > Valid category values include the enumerated values. In addition, the result of applying commutative operators | and & to any two valid values is valid, and results in the setwise union and intersection, respectively, of the argument categories. The values `all` and `none` are defined such that for any valid value `cat`, the expressions `(cat | all == all)`, `(cat & all == cat)`, `(cat | none == cat)` and `(cat & none == none)` are true. For non-equal values `cat1` and `cat2` of the remaining enumerated values, `(cat1 & cat2 == none)` is true. For any valid categories `cat1` and `cat2`, the result of `(cat1 & ~cat2)` is valid, and equals the setwise union of those categories found in `cat1` but not found in `cat2`. [Footnote: it is not required that `all` equal the setwise union of the other enumerated values; implementations may add extra categories.]

### 349. Minor typographical error in ostream_iterator

Section: 24.6.2 [ostream.iterator] Status: CD1 Submitter: Andy Sawyer Opened: 2001-10-24 Last modified: 2008-09-26

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Discussion:

24.5.2 [lib.ostream.iterator] states:

        [...]

        private:
        // basic_ostream<charT,traits>* out_stream; exposition only
        // const char* delim; exposition only

Whilst it's clearly marked "exposition only", I suspect 'delim' should be of type 'const charT*'.

Proposed resolution:

In 24.6.2 [ostream.iterator], replace `const char* delim` with `const charT* delim`.

### 352. missing fpos requirements

Section: 21.2.2 [char.traits.typedefs] Status: CD1 Submitter: Martin Sebor Opened: 2001-12-02 Last modified: 2008-09-26

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Discussion:

(1) There are no requirements on the `stateT` template parameter of `fpos` listed in 27.4.3. The interface appears to require that the type be at least Assignable and CopyConstructible (27.4.3.1, p1), and I think also DefaultConstructible (to implement the operations in Table 88).

21.1.2, p3, however, only requires that `char_traits<charT>::state_type` meet the requirements of CopyConstructible types.

(2) Additionally, the `stateT` template argument has no corresponding typedef in fpos which might make it difficult to use in generic code.

Proposed resolution:

Modify 21.1.2, p4 from

Requires: `state_type` shall meet the requirements of CopyConstructible types (20.1.3).

Requires: state_type shall meet the requirements of Assignable (23.1, p4), CopyConstructible (20.1.3), and DefaultConstructible (20.1.4) types.

Rationale:

The LWG feels this is two issues, as indicated above. The first is a defect---std::basic_fstream is unimplementable without these additional requirements---and the proposed resolution fixes it. The second is questionable; who would use that typedef? The class template fpos is used only in a very few places, all of which know the state type already. Unless motivation is provided, the second should be considered NAD.

### 354. Associative container lower/upper bound requirements

Section: 23.2.4 [associative.reqmts] Status: CD1 Submitter: Hans Aberg Opened: 2001-12-17 Last modified: 2008-09-26

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Discussion:

Discussions in the thread "Associative container lower/upper bound requirements" on comp.std.c++ suggests that there is a defect in the C++ standard, Table 69 of section 23.1.2, "Associative containers", [lib.associative.reqmts]. It currently says:

> a.find(k): returns an iterator pointing to an element with the key equivalent to k, or a.end() if such an element is not found.

> a.lower_bound(k): returns an iterator pointing to the first element with key not less than k.

> a.upper_bound(k): returns an iterator pointing to the first element with key greater than k.

We have "or a.end() if such an element is not found" for `find`, but not for `upper_bound` or `lower_bound`. As the text stands, one would be forced to insert a new element into the container and return an iterator to that in case the sought iterator does not exist, which does not seem to be the intention (and not possible with the "const" versions).

Proposed resolution:

Change Table 69 of section 23.2.4 [associative.reqmts] indicated entries to:

> a.lower_bound(k): returns an iterator pointing to the first element with key not less than k, or a.end() if such an element is not found.

> a.upper_bound(k): returns an iterator pointing to the first element with key greater than k, or a.end() if such an element is not found.

[Curaçao: LWG reviewed PR.]

### 355. Operational semantics for a.back()

Section: 23.2.3 [sequence.reqmts] Status: CD1 Submitter: Yaroslav Mironov Opened: 2002-01-23 Last modified: 2008-09-26

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Discussion:

Table 68 "Optional Sequence Operations" in 23.1.1/12 specifies operational semantics for "a.back()" as "*--a.end()", which may be ill-formed [because calling operator-- on a temporary (the return) of a built-in type is ill-formed], provided a.end() returns a simple pointer rvalue (this is almost always the case for std::vector::end(), for example). Thus, the specification is not only incorrect, it demonstrates a dangerous construct: "--a.end()" may successfully compile and run as intended, but after changing the type of the container or the mode of compilation it may produce compile-time error.

Proposed resolution:

Change the specification in table 68 "Optional Sequence Operations" in 23.1.1/12 for "a.back()" from

>     *--a.end()

to

>       { iterator tmp = a.end(); --tmp; return *tmp; }

and the specification for "a.pop_back()" from

>     a.erase(--a.end())

to

>       { iterator tmp = a.end(); --tmp; a.erase(tmp); }

[Curaçao: LWG changed PR from "{ X::iterator tmp = a.end(); return *--tmp; }" to "*a.rbegin()", and from "{ X::iterator tmp = a.end(); a.erase(--tmp); }" to "a.erase(rbegin())".]

[There is a second possible defect; table 68 "Optional Sequence Operations" in the "Operational Semantics" column uses operations present only in the "Reversible Container" requirements, yet there is no stated dependency between these separate requirements tables. Ask in Santa Cruz if the LWG would like a new issue opened.]

[Santa Cruz: the proposed resolution is even worse than what's in the current standard: erase is undefined for reverse iterator. If we're going to make the change, we need to define a temporary and use operator--. Additionally, we don't know how prevalent this is: do we need to make this change in more than one place? Martin has volunteered to review the standard and see if this problem occurs elsewhere.]

[Oxford: Matt provided new wording to address the concerns raised in Santa Cruz. It does not appear that this problem appears anywhere else in clauses 23 or 24.]

[Kona: In definition of operational semantics of back(), change "*tmp" to "return *tmp;"]

### 358. interpreting `thousands_sep` after a `decimal_point`

Section: 22.4.2.1.2 [facet.num.get.virtuals] Status: CD1 Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2008-09-26

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Discussion:

I don't think `thousands_sep` is being treated correctly after decimal_point has been seen. Since grouping applies only to the integral part of the number, the first such occurrence should, IMO, terminate Stage 2. (If it does not terminate it, then 22.2.2.1.2, p12 and 22.2.3.1.2, p3 need to explain how `thousands_sep` is to be interpreted in the fractional part of a number.)

The easiest change I can think of that resolves this issue would be something like below.

Proposed resolution:

Change the first sentence of 22.2.2.1.2, p9 from

> If discard is true then the position of the character is remembered, but the character is otherwise ignored. If it is not discarded, then a check is made to determine if c is allowed as the next character of an input field of the conversion specifier returned by stage 1. If so it is accumulated.

to

> If `discard` is true, then if `'.'` has not yet been accumulated, then the position of the character is remembered, but the character is otherwise ignored. Otherwise, if `'.'` has already been accumulated, the character is discarded and Stage 2 terminates. ...

Rationale:

We believe this reflects the intent of the Standard. Thousands sep characters after the decimal point are not useful in any locale. Some formatting conventions do group digits that follow the decimal point, but they usually introduce a different grouping character instead of reusing the thousand sep character. If we want to add support for such conventions, we need to do so explicitly.

### 359. num_put<>::do_put (..., bool) undocumented

Section: 22.4.2.2.1 [facet.num.put.members] Status: CD1 Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2008-09-26

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Discussion:

22.2.2.2.1, p1:

        iter_type put (iter_type out, ios_base& str, char_type fill,
                       bool val) const;
        ...

        1   Returns: do_put (out, str, fill, val).

AFAICS, the behavior of do_put (..., bool) is not documented anywhere, however, 22.2.2.2.2, p23:

>     iter_type put (iter_type out, ios_base& str, char_type fill,
>                    bool val) const;

> Effects: If (str.flags() & ios_base::boolalpha) == 0 then do out = do_put(out, str, fill, (int)val) Otherwise do

>                  string_type s =
>                      val ? use_facet<ctype<charT> >(loc).truename()
>                          : use_facet<ctype<charT> >(loc).falsename();

> and then insert the characters of s into out. out.

This means that the bool overload of `do_put()` will never be called, which contradicts the first paragraph. Perhaps the declaration should read `do_put()`, and not `put()`?

Note also that there is no Returns clause for this function, which should probably be corrected, just as should the second occurrence of "out." in the text.

I think the least invasive change to fix it would be something like the following:

Proposed resolution:

In 22.4.2.2.2 [facet.num.put.virtuals], just above paragraph 1, remove the `bool` overload.

In 22.4.2.2.2 [facet.num.put.virtuals], p23, make the following changes

> Replace `put()` with `do_put()` in the declaration of the member function.

> Change the Effects clause to a Returns clause (to avoid the requirement to call `do_put(..., int)` from `do_put (..., bool))` like so:

> 23 Returns: If `(str.flags() & ios_base::boolalpha) == 0` then `do_put (out, str, fill, (long)val)` Otherwise the function obtains a string `s` as if by

>                  string_type s =
>                     val ? use_facet<ctype<charT> >(loc).truename()
>                         : use_facet<ctype<charT> >(loc).falsename();

> and then inserts each character `c` of s into out via `*out++ = c` and returns `out`.

Rationale:

This fixes a couple of obvious typos, and also fixes what appears to be a requirement of gratuitous inefficiency.

### 360. locale mandates inefficient implementation

Section: 22.3.1 [locale] Status: CD1 Submitter: Martin Sebor Opened: 2002-03-12 Last modified: 2008-09-26

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Discussion:

22.1.1, p7 (copied below) allows iostream formatters and extractors to make assumptions about the values returned from facet members. However, such assumptions are apparently not guaranteed to hold in other cases (e.g., when the facet members are being called directly rather than as a result of iostream calls, or between successive calls to the same iostream functions with no interevening calls to `imbue()`, or even when the facet member functions are called from other member functions of other facets). This restriction prevents locale from being implemented efficiently.

Proposed resolution:

Change the first sentence in 22.1.1, p7 from

> In successive calls to a locale facet member function during a call to an iostream inserter or extractor or a streambuf member function, the returned result shall be identical. [Note: This implies that such results may safely be reused without calling the locale facet member function again, and that member functions of iostream classes cannot safely call `imbue()` themselves, except as specified elsewhere. --end note]

to

> In successive calls to a locale facet member function on a facet object installed in the same locale, the returned result shall be identical. ...

Rationale:

This change is reasonable becuase it clarifies the intent of this part of the standard.

### 362. bind1st/bind2nd type safety

Section: D.9 [depr.lib.binders] Status: CD1 Submitter: Andrew Demkin Opened: 2002-04-26 Last modified: 2008-09-26

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Discussion:

The definition of bind1st() (D.9 [depr.lib.binders]) can result in the construction of an unsafe binding between incompatible pointer types. For example, given a function whose first parameter type is 'pointer to T', it's possible without error to bind an argument of type 'pointer to U' when U does not derive from T:

       foo(T*, int);

       struct T {};
       struct U {};

       U u;

       int* p;
       int* q;

       for_each(p, q, bind1st(ptr_fun(foo), &u));    // unsafe binding

The definition of bind1st() includes a functional-style conversion to map its argument to the expected argument type of the bound function (see below):

      typename Operation::first_argument_type(x)

A functional-style conversion (D.9 [depr.lib.binders]) is defined to be semantically equivalent to an explicit cast expression (D.9 [depr.lib.binders]), which may (according to 5.4, paragraph 5) be interpreted as a reinterpret_cast, thus masking the error.

The problem and proposed change also apply to D.9 [depr.lib.binders].

Proposed resolution:

Add this sentence to the end of D.9 [depr.lib.binders]/1: "Binders `bind1st` and `bind2nd` are deprecated in favor of `std::tr1::bind`."

(Notes to editor: (1) when and if tr1::bind is incorporated into the standard, "std::tr1::bind" should be changed to "std::bind". (2) 20.5.6 should probably be moved to Annex D.

Rationale:

There is no point in fixing bind1st and bind2nd. tr1::bind is a superior solution. It solves this problem and others.

### 363. Missing exception specification in 27.4.2.1.1

Section: 27.5.2.1.1 [ios::failure] Status: CD1 Submitter: Walter Brown and Marc Paterno Opened: 2002-05-20 Last modified: 2008-09-26

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Discussion:

The destructor of ios_base::failure should have an empty throw specification, because the destructor of its base class, exception, is declared in this way.

Proposed resolution:

Change the destructor to

      virtual ~failure() throw();

Rationale:

Fixes an obvious glitch. This is almost editorial.

### 364. Inconsistent wording in 27.5.2.4.2

Section: 27.6.2.4.2 [streambuf.virt.buffer] Status: CD1 Submitter: Walter Brown, Marc Paterno Opened: 2002-05-10 Last modified: 2008-09-26

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Discussion:

27.6.2.4.2 [streambuf.virt.buffer] paragraph 1 is inconsistent with the Effects clause for seekoff.

Proposed resolution:

Make this paragraph, the Effects clause for setbuf, consistent in wording with the Effects clause for seekoff in paragraph 3 by amending paragraph 1 to indicate the purpose of setbuf:

Original text:

> 1 Effects: Performs an operation that is defined separately for each class derived from basic_streambuf in this clause (27.7.1.3, 27.8.1.4).

Proposed text:

> 1 Effects: Influences stream buffering in a way that is defined separately for each class derived from basic_streambuf in this clause (27.7.1.3, 27.8.1.4).

Rationale:

The LWG doesn't believe there is any normative difference between the existing wording and what's in the proposed resolution, but the change may make the intent clearer.

### 365. Lack of const-qualification in clause 27

Section: 27 [input.output] Status: CD1 Submitter: Walter Brown, Marc Paterno Opened: 2002-05-10 Last modified: 2008-09-26

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Discussion:

Some stream and streambuf member functions are declared non-const, even thought they appear only to report information rather than to change an object's logical state. They should be declared const. See document N1360 for details and rationale.

The list of member functions under discussion: `in_avail`, `showmanyc`, `tellg`, `tellp`, `is_open`.

Related issue: 73

Proposed resolution:

In 27.8.1.5, 27.8.1.7, 27.8.1.8, 27.8.1.10, 27.8.1.11, and 27.8.1.13

Replace

      bool is_open();

with

      bool is_open() const;

Rationale:

Of the changes proposed in N1360, the only one that is safe is changing the filestreams' is_open to const. The LWG believed that this was NAD the first time it considered this issue (issue 73), but now thinks otherwise. The corresponding streambuf member function, after all,is already const.

The other proposed changes are less safe, because some streambuf functions that appear merely to report a value do actually perform mutating operations. It's not even clear that they should be considered "logically const", because streambuf has two interfaces, a public one and a protected one. These functions may, and often do, change the state as exposed by the protected interface, even if the state exposed by the public interface is unchanged.

Note that implementers can make this change in a binary compatible way by providing both overloads; this would be a conforming extension.

### 369. io stream objects and static ctors

Section: 27.4 [iostream.objects] Status: CD1 Submitter: Ruslan Abdikeev Opened: 2002-07-08 Last modified: 2008-09-26

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Discussion:

Is it safe to use standard iostream objects from constructors of static objects? Are standard iostream objects constructed and are their associations established at that time?

Surpisingly enough, Standard does NOT require that.

27.3/2 [lib.iostream.objects] guarantees that standard iostream objects are constructed and their associations are established before the body of main() begins execution. It also refers to ios_base::Init class as the panacea for constructors of static objects.

However, there's nothing in 27.3 [lib.iostream.objects], in 27.4.2 [lib.ios.base], and in 27.4.2.1.6 [lib.ios::Init], that would require implementations to allow access to standard iostream objects from constructors of static objects.

Details:

Core text refers to some magic object ios_base::Init, which will be discussed below:

> "The [standard iostream] objects are constructed, and their associations are established at some time prior to or during first time an object of class basic_ios<charT,traits>::Init is constructed, and in any case before the body of main begins execution." (27.3/2 [lib.iostream.objects])

The first non-normative footnote encourages implementations to initialize standard iostream objects earlier than required.

However, the second non-normative footnote makes an explicit and unsupported claim:

> "Constructors and destructors for static objects can access these [standard iostream] objects to read input from stdin or write output to stdout or stderr." (27.3/2 footnote 265 [lib.iostream.objects])

The only bit of magic is related to that ios_base::Init class. AFAIK, the rationale behind ios_base::Init was to bring an instance of this class to each translation unit which #included <iostream> or related header. Such an inclusion would support the claim of footnote quoted above, because in order to use some standard iostream object it is necessary to #include <iostream>.

However, while Standard explicitly describes ios_base::Init as an appropriate class for doing the trick, I failed to found a mention of an _instance_ of ios_base::Init in Standard.

Proposed resolution:

Add to 27.4 [iostream.objects], p2, immediately before the last sentence of the paragraph, the following two sentences:

> If a translation unit includes <iostream>, or explicitly constructs an ios_base::Init object, these stream objects shall be constructed before dynamic initialization of non-local objects defined later in that translation unit, and these stream objects shall be destroyed after the destruction of dynamically initialized non-local objects defined later in that translation unit.

[Lillehammer: Matt provided wording.]

[Mont Tremblant: Matt provided revised wording.]

Rationale:

The original proposed resolution unconditionally required implementations to define an ios_base::Init object of some implementation-defined name in the header <iostream>. That's an overspecification. First, defining the object may be unnecessary and even detrimental to performance if an implementation can guarantee that the 8 standard iostream objects will be initialized before any other user-defined object in a program. Second, there is no need to require implementations to document the name of the object.

The new proposed resolution gives users guidance on what they need to do to ensure that stream objects are constructed during startup.

### 370. Minor error in basic_istream::get

Section: 27.7.1.3 [istream.unformatted] Status: CD1 Submitter: Ray Lischner Opened: 2002-07-15 Last modified: 2008-09-26

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Discussion:

Defect report for description of basic_istream::get (section 27.7.1.3 [istream.unformatted]), paragraph 15. The description for the get function with the following signature:

      basic_istream<charT,traits>& get(basic_streambuf<char_type,traits>&
      sb);

is incorrect. It reads

> Effects: Calls get(s,n,widen('\n'))

which I believe should be:

> Effects: Calls get(sb,widen('\n'))

Proposed resolution:

Change the Effects paragraph to:

> Effects: Calls get(sb,this->widen('\n'))

[Pre-Oxford: Minor correction from Howard: replaced 'widen' with 'this->widen'.]

Rationale:

Fixes an obvious typo.

### 371. Stability of multiset and multimap member functions

Section: 23.2 [container.requirements] Status: CD1 Submitter: Frank Compagner Opened: 2002-07-20 Last modified: 2008-09-26

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Discussion:

The requirements for multiset and multimap containers (23.1 [lib.containers.requirements], 23.1.2 [lib.associative.reqmnts], 23.3.2 [lib.multimap] and 23.3.4 [lib.multiset]) make no mention of the stability of the required (mutating) member functions. It appears the standard allows these functions to reorder equivalent elements of the container at will, yet the pervasive red-black tree implementation appears to provide stable behaviour.

This is of most concern when considering the behaviour of erase(). A stability requirement would guarantee the correct working of the following 'idiom' that removes elements based on a certain predicate function.

      multimap<int, int> m;
      multimap<int, int>::iterator i = m.begin();
      while (i != m.end()) {
          if (pred(i))
              m.erase (i++);
          else
              ++i;
      }

Although clause 23.1.2/8 guarantees that i remains a valid iterator througout this loop, absence of the stability requirement could potentially result in elements being skipped. This would make this code incorrect, and, furthermore, means that there is no way of erasing these elements without iterating first over the entire container, and second over the elements to be erased. This would be unfortunate, and have a negative impact on both performance and code simplicity.

If the stability requirement is intended, it should be made explicit (probably through an extra paragraph in clause 23.1.2).

If it turns out stability cannot be guaranteed, i'd argue that a remark or footnote is called for (also somewhere in clause 23.1.2) to warn against relying on stable behaviour (as demonstrated by the code above). If most implementations will display stable behaviour, any problems emerging on an implementation without stable behaviour will be hard to track down by users. This would also make the need for an erase_if() member function that much greater.

This issue is somewhat related to LWG issue 130.

Proposed resolution:

Add the following to the end of 23.2.4 [associative.reqmts] paragraph 4: "For `multiset` and `multimap`, `insert`and `erase` are stable: they preserve the relative ordering of equivalent elements.

[Lillehammer: Matt provided wording]

[Joe Gottman points out that the provided wording does not address multimap and multiset. N1780 also addresses this issue and suggests wording.]

[Mont Tremblant: Changed set and map to multiset and multimap.]

Rationale:

The LWG agrees that this guarantee is necessary for common user idioms to work, and that all existing implementations provide this property. Note that this resolution guarantees stability for multimap and multiset, not for all associative containers in general.

### 373. Are basic_istream and basic_ostream to use (exceptions()&badbit) != 0 ?

Section: 27.7.1.2.1 [istream.formatted.reqmts], 27.7.2.6.1 [ostream.formatted.reqmts] Status: CD1 Submitter: Keith Baker Opened: 2002-07-23 Last modified: 2008-09-26

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Discussion:

In 27.7.1.2.1 [istream.formatted.reqmts] and 27.7.2.6.1 [ostream.formatted.reqmts] (exception()&badbit) != 0 is used in testing for rethrow, yet exception() is the constructor to class std::exception in 18.7.1 [type.info] that has no return type. Should member function exceptions() found in 27.5.4 [ios] be used instead?

Proposed resolution:

In 27.7.1.2.1 [istream.formatted.reqmts] and 27.7.2.6.1 [ostream.formatted.reqmts], change "(exception()&badbit) != 0" to "(exceptions()&badbit) != 0".

Rationale:

Fixes an obvious typo.

### 375. basic_ios should be ios_base in 27.7.1.3

Section: 27.8.1.4 [stringbuf.virtuals] Status: CD1 Submitter: Ray Lischner Opened: 2002-08-14 Last modified: 2008-09-26

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Discussion:

In Section 27.8.1.4 [stringbuf.virtuals]: Table 90, Table 91, and paragraph 14 all contain references to "basic_ios::" which should be "ios_base::".

Proposed resolution:

Change all references to "basic_ios" in Table 90, Table 91, and paragraph 14 to "ios_base".

Rationale:

Fixes an obvious typo.

### 376. basic_streambuf semantics

Section: 27.8.1.4 [stringbuf.virtuals] Status: CD1 Submitter: Ray Lischner Opened: 2002-08-14 Last modified: 2008-09-26

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Discussion:

In Section 27.8.1.4 [stringbuf.virtuals], Table 90, the implication is that the four conditions should be mutually exclusive, but they are not. The first two cases, as written, are subcases of the third.

As written, it is unclear what should be the result if cases 1 and 2 are both true, but case 3 is false.

Proposed resolution:

Rewrite these conditions as:

> (which & (ios_base::in|ios_base::out)) == ios_base::in

> (which & (ios_base::in|ios_base::out)) == ios_base::out

> (which & (ios_base::in|ios_base::out)) == (ios_base::in|ios_base::out) and way == either ios_base::beg or ios_base::end

> Otherwise

Rationale:

It's clear what we wanted to say, we just failed to say it. This fixes it.

### 379. nonsensical ctype::do_widen() requirement

Section: 22.4.1.1.2 [locale.ctype.virtuals] Status: CD1 Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2008-09-26

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Discussion:

The last sentence in 22.2.1.1.2, p11 below doesn't seem to make sense.

      charT do_widen (char c) const;

      -11- Effects: Applies the simplest reasonable transformation from
           a char value or sequence of char values to the corresponding
           charT value or values. The only characters for which unique
           transformations are required are those in the basic source
           character set (2.2). For any named ctype category with a
           ctype<charT> facet ctw and valid ctype_base::mask value
           M (is(M, c) || !ctw.is(M, do_widen(c))) is true.

Shouldn't the last sentence instead read

           For any named ctype category with a ctype<char> facet ctc
           and valid ctype_base::mask value M
           (ctc.is(M, c) || !is(M, do_widen(c))) is true.

I.e., if the narrow character c is not a member of a class of characters then neither is the widened form of c. (To paraphrase footnote 224.)

Proposed resolution:

Replace the last sentence of 22.4.1.1.2 [locale.ctype.virtuals], p11 with the following text:

           For any named ctype category with a ctype<char> facet ctc
           and valid ctype_base::mask value M,
           (ctc.is(M, c) || !is(M, do_widen(c))) is true.

[Kona: Minor edit. Added a comma after the M for clarity.]

Rationale:

The LWG believes this is just a typo, and that this is the correct fix.

### 380. typos in codecvt tables 53 and 54

Section: 22.4.1.5 [locale.codecvt.byname] Status: CD1 Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2008-09-26

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Discussion:

Tables 53 and 54 in 22.4.1.5 [locale.codecvt.byname] are both titled "convert result values," when surely "do_in/do_out result values" must have been intended for Table 53 and "do_unshift result values" for Table 54.

Table 54, row 3 says that the meaning of partial is "more characters needed to be supplied to complete termination." The function is not supplied any characters, it is given a buffer which it fills with characters or, more precisely, destination elements (i.e., an escape sequence). So partial means that space for more than (to_limit - to) destination elements was needed to terminate a sequence given the value of state.

Proposed resolution:

Change the title of Table 53 to "do_in/do_out result values" and the title of Table 54 to "do_unshift result values."

Change the text in Table 54, row 3 (the partial row), under the heading Meaning, to "space for more than (to_limit - to) destination elements was needed to terminate a sequence given the value of state."

### 381. detection of invalid mbstate_t in codecvt

Section: 22.4.1.5 [locale.codecvt.byname] Status: CD1 Submitter: Martin Sebor Opened: 2002-09-06 Last modified: 2008-09-26

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Discussion:

All but one codecvt member functions that take a state_type argument list as one of their preconditions that the state_type argument have a valid value. However, according to 22.2.1.5.2, p6, codecvt::do_unshift() is the only codecvt member that is supposed to return error if the state_type object is invalid.

It seems to me that the treatment of state_type by all codecvt member functions should be the same and the current requirements should be changed. Since the detection of invalid state_type values may be difficult in general or computationally expensive in some specific cases, I propose the following:

Proposed resolution:

Add a new paragraph before 22.2.1.5.2, p5, and after the function declaration below

        result do_unshift(stateT& state,
        externT* to, externT* to_limit, externT*& to_next) const;

as follows:

        Requires: (to <= to_end) well defined and true; state initialized,
        if at the beginning of a sequence, or else equal to the result of
        converting the preceding characters in the sequence.

and change the text in Table 54, row 4, the error row, under the heading Meaning, from

        state has invalid value

to

        an unspecified error has occurred

Rationale:

The intent is that implementations should not be required to detect invalid state values; such a requirement appears nowhere else. An invalid state value is a precondition violation, i.e. undefined behavior. Implementations that do choose to detect invalid state values, or that choose to detect any other kind of error, may return error as an indication.

### 383. Bidirectional iterator assertion typo

Section: 24.2.4 [bidirectional.iterators] Status: CD1 Submitter: ysapir (submitted via comp.std.c++) Opened: 2002-10-17 Last modified: 2008-09-26

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Discussion:

Following a discussion on the boost list regarding end iterators and the possibility of performing operator--() on them, it seems to me that there is a typo in the standard. This typo has nothing to do with that discussion.

I have checked this newsgroup, as well as attempted a search of the Active/Defect/Closed Issues List on the site for the words "s is derefer" so I believe this has not been proposed before. Furthermore, the "Lists by Index" mentions only DR 299 on section 24.1.4, and DR 299 is not related to this issue.

The standard makes the following assertion on bidirectional iterators, in section 24.1.4 [lib.bidirectional.iterators], Table 75:

                             operational  assertion/note
    expression  return type   semantics    pre/post-condition

    --r          X&                        pre: there exists s such
                                           that r == ++s.
                                           post: s is dereferenceable.
                                           --(++r) == r.
                                           --r == --s implies r == s.
                                           &r == &--r.

(See http://aspn.activestate.com/ASPN/Mail/Message/boost/1395763.)

In particular, "s is dereferenceable" seems to be in error. It seems that the intention was to say "r is dereferenceable".

If it were to say "r is dereferenceable" it would make perfect sense. Since s must be dereferenceable prior to operator++, then the natural result of operator-- (to undo operator++) would be to make r dereferenceable. Furthermore, without other assertions, and basing only on precondition and postconditions, we could not otherwise know this. So it is also interesting information.

Proposed resolution:

Change the guarantee to "postcondition: r is dereferenceable."

Rationale:

Fixes an obvious typo

### 384. equal_range has unimplementable runtime complexity

Section: 25.4.3.3 [equal.range] Status: CD1 Submitter: Hans Bos Opened: 2002-10-18 Last modified: 2008-09-26

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Discussion:

Section 25.4.3.3 [equal.range] states that at most 2 * log(last - first) + 1 comparisons are allowed for equal_range.

It is not possible to implement equal_range with these constraints.

In a range of one element as in:

        int x = 1;
        equal_range(&x, &x + 1, 1)

it is easy to see that at least 2 comparison operations are needed.

For this case at most 2 * log(1) + 1 = 1 comparison is allowed.

I have checked a few libraries and they all use the same (nonconforming) algorithm for equal_range that has a complexity of

         2* log(distance(first, last)) + 2.

I guess this is the algorithm that the standard assumes for equal_range.

It is easy to see that 2 * log(distance) + 2 comparisons are enough since equal range can be implemented with lower_bound and upper_bound (both log(distance) + 1).

I think it is better to require something like 2log(distance) + O(1) (or even logarithmic as multiset::equal_range). Then an implementation has more room to optimize for certain cases (e.g. have log(distance) characteristics when at most match is found in the range but 2log(distance) + 4 for the worst case).

Proposed resolution:

In 25.4.3.1 [lower.bound]/4, change `log(last - first) + 1` to `log2(last - first) + O(1)`.

In 25.4.3.2 [upper.bound]/4, change `log(last - first) + 1` to `log2(last - first) + O(1)`.

In 25.4.3.3 [equal.range]/4, change `2*log(last - first) + 1` to `2*log2(last - first) + O(1)`.

[Matt provided wording]

Rationale:

The LWG considered just saying O(log n) for all three, but decided that threw away too much valuable information. The fact that lower_bound is twice as fast as equal_range is important. However, it's better to allow an arbitrary additive constant than to specify an exact count. An exact count would have to involve `floor` or `ceil`. It would be too easy to get this wrong, and don't provide any substantial value for users.

### 386. Reverse iterator's operator[] has impossible return type

Section: 24.5.1.3.11 [reverse.iter.op-=] Status: CD1 Submitter: Matt Austern Opened: 2002-10-23 Last modified: 2009-05-01

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Discussion:

In 24.5.1.3.11 [reverse.iter.op-=], `reverse_iterator<>::operator[]` is specified as having a return type of `reverse_iterator::reference`, which is the same as `iterator_traits<Iterator>::reference`. (Where `Iterator` is the underlying iterator type.)

The trouble is that `Iterator`'s own operator[] doesn't necessarily have a return type of `iterator_traits<Iterator>::reference`. Its return type is merely required to be convertible to `Iterator`'s value type. The return type specified for reverse_iterator's operator[] would thus appear to be impossible.

With the resolution of issue 299, the type of `a[n]` will continue to be required (for random access iterators) to be convertible to the value type, and also `a[n] = t` will be a valid expression. Implementations of `reverse_iterator` will likely need to return a proxy from `operator[]` to meet these requirements. As mentioned in the comment from Dave Abrahams, the simplest way to specify that `reverse_iterator` meet this requirement to just mandate it and leave the return type of `operator[]` unspecified.

Proposed resolution:

In 24.5.1.2 [reverse.iter.requirements] change:

>     reference operator[](difference_type n) const;

to:

>     unspecified operator[](difference_type n) const; // see 24.2.5 [random.access.iterators]

[ Comments from Dave Abrahams: IMO we should resolve 386 by just saying that the return type of reverse_iterator's operator[] is unspecified, allowing the random access iterator requirements to impose an appropriate return type. If we accept 299's proposed resolution (and I think we should), the return type will be readable and writable, which is about as good as we can do. ]

### 387. std::complex over-encapsulated

Section: 26.4 [complex.numbers] Status: CD1 Submitter: Gabriel Dos Reis Opened: 2002-11-08 Last modified: 2008-09-26

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Discussion:

The absence of explicit description of std::complex<T> layout makes it imposible to reuse existing software developed in traditional languages like Fortran or C with unambigous and commonly accepted layout assumptions. There ought to be a way for practitioners to predict with confidence the layout of std::complex<T> whenever T is a numerical datatype. The absence of ways to access individual parts of a std::complex<T> object as lvalues unduly promotes severe pessimizations. For example, the only way to change, independently, the real and imaginary parts is to write something like

    complex<T> z;
    // ...
    // set the real part to r
    z = complex<T>(r, z.imag());
    // ...
    // set the imaginary part to i
    z = complex<T>(z.real(), i);

At this point, it seems appropriate to recall that a complex number is, in effect, just a pair of numbers with no particular invariant to maintain. Existing practice in numerical computations has it that a complex number datatype is usually represented by Cartesian coordinates. Therefore the over-encapsulation put in the specification of std::complex<> is not justified.

Proposed resolution:

Add the following requirements to 26.4 [complex.numbers] as 26.3/4:

> If z is an lvalue expression of type cv std::complex<T> then

> - the expression reinterpret_cast<cv T(&)[2]>(z) is well-formed; and
> - reinterpret_cast<cv T(&)[2]>(z)[0]designates the real part of z; and
> - reinterpret_cast<cv T(&)[2]>(z)[1]designates the imaginary part of z.

> Moreover, if a is an expression of pointer type cv complex<T>* and the expression a[i] is well-defined for an integer expression i then:

> - reinterpret_cast<cv T*>(a)[2*i] designates the real part of a[i]; and
> - reinterpret_cast<cv T*>(a)[2*i+1] designates the imaginary part of a[i].

In 26.4.2 [complex] and 26.4.3 [complex.special] add the following member functions (changing `T` to concrete types as appropriate for the specializations).

>     void real(T);
>     void imag(T);

Add to 26.4.4 [complex.members]

>     T real() const;

> > Returns: the value of the real component

>     void real(T val);

> > Assigns val to the real component.

>     T imag() const;

> > Returns: the value of the imaginary component

>     void imag(T val);

> > Assigns val to the imaginary component.

[Kona: The layout guarantee is absolutely necessary for C compatibility. However, there was disagreement about the other part of this proposal: retrieving elements of the complex number as lvalues. An alternative: continue to have real() and imag() return rvalues, but add set_real() and set_imag(). Straw poll: return lvalues - 2, add setter functions - 5. Related issue: do we want reinterpret_cast as the interface for converting a complex to an array of two reals, or do we want to provide a more explicit way of doing it? Howard will try to resolve this issue for the next meeting.]

[pre-Sydney: Howard summarized the options in n1589.]

[ Bellevue: ]

> Second half of proposed wording replaced and moved to Ready.

[ Pre-Sophia Antipolis, Howard adds: ]

> Added the members to 26.4.3 [complex.special] and changed from Ready to Review.

[ Post-Sophia Antipolis: ]

> Moved from WP back to Ready so that the "and 26.4.3 [complex.special]" in the proposed resolution can be officially applied.

Rationale:

The LWG believes that C99 compatibility would be enough justification for this change even without other considerations. All existing implementations already have the layout proposed here.

### 389. Const overload of valarray::operator[] returns by value

Section: 26.6.2.3 [valarray.access] Status: CD1 Submitter: Gabriel Dos Reis Opened: 2002-11-08 Last modified: 2008-09-26

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Duplicate of: 77

Discussion:

Consider the following program:

        #include <iostream>
        #include <ostream>
        #include <vector>
        #include <valarray>
        #include <algorithm>
        #include <iterator>
        template<typename Array>
        void print(const Array& a)
        {
        using namespace std;
        typedef typename Array::value_type T;
        copy(&a[0], &a[0] + a.size(),
        ostream_iterator<T>(std::cout, " "));
        }
        template<typename T, unsigned N>
        unsigned size(T(&)[N]) { return N; }
        int main()
        {
        double array[] = { 0.89, 9.3, 7, 6.23 };
        std::vector<double> v(array, array + size(array));
        std::valarray<double> w(array, size(array));
        print(v); // #1
        std::cout << std::endl;
        print(w); // #2
        std::cout << std::endl;
        }

While the call numbered #1 succeeds, the call numbered #2 fails because the const version of the member function valarray<T>::operator[](size_t) returns a value instead of a const-reference. That seems to be so for no apparent reason, no benefit. Not only does that defeats users' expectation but it also does hinder existing software (written either in C or Fortran) integration within programs written in C++. There is no reason why subscripting an expression of type valarray<T> that is const-qualified should not return a const T&.

Proposed resolution:

In the class synopsis in 26.6.2 [template.valarray], and in 26.6.2.3 [valarray.access] just above paragraph 1, change

      T operator[](size_t const);

to

      const T& operator[](size_t const);

[Kona: fixed a minor typo: put semicolon at the end of the line wehre it belongs.]

Rationale:

Return by value seems to serve no purpose. Valaray was explicitly designed to have a specified layout so that it could easily be integrated with libraries in other languages, and return by value defeats that purpose. It is believed that this change will have no impact on allowable optimizations.

### 391. non-member functions specified as const

Section: 22.3.3.2 [conversions] Status: CD1 Submitter: James Kanze Opened: 2002-12-10 Last modified: 2008-09-26

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Discussion:

The specifications of toupper and tolower both specify the functions as const, althought they are not member functions, and are not specified as const in the header file synopsis in section 22.3 [locales].

Proposed resolution:

In 22.3.3.2 [conversions], remove `const` from the function declarations of std::toupper and std::tolower

Rationale:

Fixes an obvious typo

### 395. inconsistencies in the definitions of rand() and random_shuffle()

Section: 26.8 [c.math] Status: CD1 Submitter: James Kanze Opened: 2003-01-03 Last modified: 2008-09-26

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Discussion:

In 26.8 [c.math], the C++ standard refers to the C standard for the definition of rand(); in the C standard, it is written that "The implementation shall behave as if no library function calls the rand function."

In 25.3.12 [alg.random.shuffle], there is no specification as to how the two parameter version of the function generates its random value. I believe that all current implementations in fact call rand() (in contradiction with the requirement avove); if an implementation does not call rand(), there is the question of how whatever random generator it does use is seeded. Something is missing.

Proposed resolution:

In [lib.c.math], add a paragraph specifying that the C definition of rand shal be modified to say that "Unless otherwise specified, the implementation shall behave as if no library function calls the rand function."

In [lib.alg.random.shuffle], add a sentence to the effect that "In the two argument form of the function, the underlying source of random numbers is implementation defined. [Note: in particular, an implementation is permitted to use `rand`.]

Rationale:

The original proposed resolution proposed requiring the two-argument from of `random_shuffle` to use `rand`. We don't want to do that, because some existing implementations already use something else: gcc uses `lrand48`, for example. Using `rand` presents a problem if the number of elements in the sequence is greater than RAND_MAX.

### 396. what are characters zero and one

Section: 20.3.7.1 [bitset.cons] Status: CD1 Submitter: Martin Sebor Opened: 2003-01-05 Last modified: 2008-09-26

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Discussion:

23.3.5.1, p6 [lib.bitset.cons] talks about a generic character having the value of 0 or 1 but there is no definition of what that means for charT other than char and wchar_t. And even for those two types, the values 0 and 1 are not actually what is intended -- the values '0' and '1' are. This, along with the converse problem in the description of to_string() in 23.3.5.2, p33, looks like a defect remotely related to DR 303.

http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#303

    23.3.5.1:
      -6-  An element of the constructed string has value zero if the
           corresponding character in str, beginning at position pos,
           is 0. Otherwise, the element has the value one.

    23.3.5.2:
      -33-  Effects: Constructs a string object of the appropriate
            type and initializes it to a string of length N characters.
            Each character is determined by the value of its
            corresponding bit position in *this. Character position N
            ?- 1 corresponds to bit position zero. Subsequent decreasing
            character positions correspond to increasing bit positions.
            Bit value zero becomes the character 0, bit value one becomes
            the character 1.

Also note the typo in 23.3.5.1, p6: the object under construction is a bitset, not a string.

[ Sophia Antipolis: ]

> We note that `bitset` has been moved from section 23 to section 20, by another issue (842) previously resolved at this meeting.

> Disposition: move to ready.

> We request that Howard submit a separate issue regarding the three to_string overloads.

Proposed resolution:

Change the constructor's function declaration immediately before 20.3.7.1 [bitset.cons] p3 to:

        template <class charT, class traits, class Allocator>
        explicit
        bitset(const basic_string<charT, traits, Allocator>& str,
               typename basic_string<charT, traits, Allocator>::size_type pos = 0,
               typename basic_string<charT, traits, Allocator>::size_type n =
                 basic_string<charT, traits, Allocator>::npos,
               charT zero = charT('0'), charT one = charT('1'))

Change the first two sentences of 20.3.7.1 [bitset.cons] p6 to: "An element of the constructed string has value 0 if the corresponding character in str, beginning at position pos, is zero. Otherwise, the element has the value 1.

Change the text of the second sentence in 23.3.5.1, p5 to read: "The function then throws invalid_argument if any of the rlen characters in str beginning at position pos is other than zero or one. The function uses traits::eq() to compare the character values."

Change the declaration of the `to_string` member function immediately before 20.3.7.2 [bitset.members] p33 to:

        template <class charT, class traits, class Allocator>
        basic_string<charT, traits, Allocator>
        to_string(charT zero = charT('0'), charT one = charT('1')) const;

Change the last sentence of 20.3.7.2 [bitset.members] p33 to: "Bit value 0 becomes the character `zero`, bit value 1 becomes the character `one`.

Change 20.3.7.3 [bitset.operators] p8 to:

Returns:

      os << x.template to_string<charT,traits,allocator<charT> >(
          use_facet<ctype<charT> >(os.getloc()).widen('0'),
          use_facet<ctype<charT> >(os.getloc()).widen('1'));

Rationale:

There is a real problem here: we need the character values of '0' and '1', and we have no way to get them since strings don't have imbued locales. In principle the "right" solution would be to provide an extra object, either a ctype facet or a full locale, which would be used to widen '0' and '1'. However, there was some discomfort about using such a heavyweight mechanism. The proposed resolution allows those users who care about this issue to get it right.

We fix the inserter to use the new arguments. Note that we already fixed the analogous problem with the extractor in issue 303.

[ post Bellevue: ]

> We are happy with the resolution as proposed, and we move this to Ready.

[ Howard adds: ]

> The proposed wording neglects the 3 newer to_string overloads.

### 400. redundant type cast in lib.allocator.members

Section: 20.8.8.1 [allocator.members] Status: CD1 Submitter: Markus Mauhart Opened: 2003-02-27 Last modified: 2008-09-26

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Discussion:

20.8.8.1 [allocator.members] allocator members, contains the following 3 lines:

      12 Returns: new((void *) p) T( val)
         void destroy(pointer p);
      13 Returns: ((T*) p)->~T()

The type cast "(T*) p" in the last line is redundant cause we know that std::allocator<T>::pointer is a typedef for T*.

Proposed resolution:

Replace "((T*) p)" with "p".

Rationale:

Just a typo, this is really editorial.

### 401. incorrect type casts in table 32 in lib.allocator.requirements

Section: 20.2.2 [allocator.requirements] Status: CD1 Submitter: Markus Mauhart Opened: 2003-02-27 Last modified: 2008-09-26

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Discussion:

I think that in par2 of [default.con.req] the last two lines of table 32 contain two incorrect type casts. The lines are ...

      a.construct(p,t)   Effect: new((void*)p) T(t)
      a.destroy(p)       Effect: ((T*)p)?->~T()

.... with the prerequisits coming from the preceding two paragraphs, especially from table 31:

      alloc<T>             a     ;// an allocator for T
      alloc<T>::pointer    p     ;// random access iterator
                                  // (may be different from T*)
      alloc<T>::reference  r = *p;// T&
      T const&             t     ;

For that two type casts ("(void*)p" and "(T*)p") to be well-formed this would require then conversions to T* and void* for all alloc<T>::pointer, so it would implicitely introduce extra requirements for alloc<T>::pointer, additionally to the only current requirement (being a random access iterator).

Proposed resolution:

Accept proposed wording from N2436 part 1.

Note: Actually I would prefer to replace "((T*)p)?->dtor_name" with "p?->dtor_name", but AFAICS this is not possible cause of an omission in 13.5.6 [over.ref] (for which I have filed another DR on 29.11.2002).

[Kona: The LWG thinks this is somewhere on the border between Open and NAD. The intend is clear: `construct` constructs an object at the location p. It's reading too much into the description to think that literally calling `new` is required. Tweaking this description is low priority until we can do a thorough review of allocators, and, in particular, allocators with non-default pointer types.]

[ Batavia: Proposed resolution changed to less code and more description. ]

[ post Oxford: This would be rendered NAD Editorial by acceptance of N2257. ]

[ Kona (2007): The LWG adopted the proposed resolution of N2387 for this issue which was subsequently split out into a separate paper N2436 for the purposes of voting. The resolution in N2436 addresses this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 402. wrong new expression in [some_]allocator::construct

Section: 20.2.2 [allocator.requirements], 20.8.8.1 [allocator.members] Status: CD1 Submitter: Markus Mauhart Opened: 2003-02-27 Last modified: 2008-09-26

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Discussion:

This applies to the new expression that is contained in both par12 of 20.8.8.1 [allocator.members] and in par2 (table 32) of [default.con.req]. I think this new expression is wrong, involving unintended side effects.

20.8.8.1 [allocator.members] contains the following 3 lines:

      11 Returns: the largest value N for which the call allocate(N,0) might succeed.
         void construct(pointer p, const_reference val);
      12 Returns: new((void *) p) T( val)

[default.con.req] in table 32 has the following line:

      a.construct(p,t)   Effect: new((void*)p) T(t)

.... with the prerequisits coming from the preceding two paragraphs, especially from table 31:

      alloc<T>             a     ;// an allocator for T
      alloc<T>::pointer    p     ;// random access iterator
                                  // (may be different from T*)
      alloc<T>::reference  r = *p;// T&
      T const&             t     ;

Cause of using "new" but not "::new", any existing "T::operator new" function will hide the global placement new function. When there is no "T::operator new" with adequate signature, every_alloc<T>::construct(..) is ill-formed, and most std::container<T,every_alloc<T>> use it; a workaround would be adding placement new and delete functions with adequate signature and semantic to class T, but class T might come from another party. Maybe even worse is the case when T has placement new and delete functions with adequate signature but with "unknown" semantic: I dont like to speculate about it, but whoever implements any_container<T,any_alloc> and wants to use construct(..) probably must think about it.

Proposed resolution:

Replace "new" with "::new" in both cases.

### 403. basic_string::swap should not throw exceptions

Section: 21.4.6.8 [string::swap] Status: CD1 Submitter: Beman Dawes Opened: 2003-03-25 Last modified: 2008-09-26

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Discussion:

std::basic_string, 21.4 [basic.string] paragraph 2 says that basic_string "conforms to the requirements of a Sequence, as specified in (23.1.1)." The sequence requirements specified in (23.1.1) to not include any prohibition on swap members throwing exceptions.

Section 23.2 [container.requirements] paragraph 10 does limit conditions under which exceptions may be thrown, but applies only to "all container types defined in this clause" and so excludes basic_string::swap because it is defined elsewhere.

Eric Niebler points out that 21.4 [basic.string] paragraph 5 explicitly permits basic_string::swap to invalidates iterators, which is disallowed by 23.2 [container.requirements] paragraph 10. Thus the standard would be contradictory if it were read or extended to read as having basic_string meet 23.2 [container.requirements] paragraph 10 requirements.

Yet several LWG members have expressed the belief that the original intent was that basic_string::swap should not throw exceptions as specified by 23.2 [container.requirements] paragraph 10, and that the standard is unclear on this issue. The complexity of basic_string::swap is specified as "constant time", indicating the intent was to avoid copying (which could cause a bad_alloc or other exception). An important use of swap is to ensure that exceptions are not thrown in exception-safe code.

Note: There remains long standing concern over whether or not it is possible to reasonably meet the 23.2 [container.requirements] paragraph 10 swap requirements when allocators are unequal. The specification of basic_string::swap exception requirements is in no way intended to address, prejudice, or otherwise impact that concern.

Proposed resolution:

In 21.4.6.8 [string::swap], add a throws clause:

Throws: Shall not throw exceptions.

### 404. May a replacement allocation function be declared inline?

Section: 17.6.3.6 [replacement.functions], 18.6.1 [new.delete] Status: CD1 Submitter: Matt Austern Opened: 2003-04-24 Last modified: 2008-09-26

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Discussion:

The eight basic dynamic memory allocation functions (single-object and array versions of ::operator new and ::operator delete, in the ordinary and nothrow forms) are replaceable. A C++ program may provide an alternative definition for any of them, which will be used in preference to the implementation's definition.

Three different parts of the standard mention requirements on replacement functions: 17.6.3.6 [replacement.functions], 18.6.1.1 [new.delete.single] and 18.6.1.2 [new.delete.array], and 3.7.3 [basic.stc.auto].

None of these three places say whether a replacement function may be declared inline. 18.6.1.1 [new.delete.single] paragraph 2 specifies a signature for the replacement function, but that's not enough: the `inline` specifier is not part of a function's signature. One might also reason from 7.1.2 [dcl.fct.spec] paragraph 2, which requires that "an inline function shall be defined in every translation unit in which it is used," but this may not be quite specific enough either. We should either explicitly allow or explicitly forbid inline replacement memory allocation functions.

Proposed resolution:

Add a new sentence to the end of 17.6.3.6 [replacement.functions] paragraph 3: "The program's definitions shall not be specified as `inline`. No diagnostic is required."

[Kona: added "no diagnostic is required"]

Rationale:

The fact that `inline` isn't mentioned appears to have been nothing more than an oversight. Existing implementations do not permit inline functions as replacement memory allocation functions. Providing this functionality would be difficult in some cases, and is believed to be of limited value.

### 405. qsort and POD

Section: 25.5 [alg.c.library] Status: CD1 Submitter: Ray Lischner Opened: 2003-04-08 Last modified: 2008-09-26

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Discussion:

Section 25.5 [alg.c.library] describes bsearch and qsort, from the C standard library. Paragraph 4 does not list any restrictions on qsort, but it should limit the base parameter to point to POD. Presumably, qsort sorts the array by copying bytes, which requires POD.

Proposed resolution:

In 25.5 [alg.c.library] paragraph 4, just after the declarations and before the nonnormative note, add these words: "both of which have the same behavior as the original declaration. The behavior is undefined unless the objects in the array pointed to by base are of POD type."

[Something along these lines is clearly necessary. Matt provided wording.]

### 406. vector::insert(s) exception safety

Section: 23.3.6.4 [vector.modifiers] Status: CD1 Submitter: Dave Abrahams Opened: 2003-04-27 Last modified: 2009-05-01

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Discussion:

There is a possible defect in the standard: the standard text was never intended to prevent arbitrary ForwardIterators, whose operations may throw exceptions, from being passed, and it also wasn't intended to require a temporary buffer in the case where ForwardIterators were passed (and I think most implementations don't use one). As is, the standard appears to impose requirements that aren't met by any existing implementation.

Proposed resolution:

Replace 23.3.6.4 [vector.modifiers] paragraph 1 with:

> 1- Notes: Causes reallocation if the new size is greater than the old capacity. If no reallocation happens, all the iterators and references before the insertion point remain valid. If an exception is thrown other than by the copy constructor or assignment operator of T or by any InputIterator operation there are no effects.

[We probably need to say something similar for deque.]

### 407. Can singular iterators be destroyed?

Section: X [iterator.concepts] Status: CD1 Submitter: Nathan Myers Opened: 2003-06-03 Last modified: 2008-09-30

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Discussion:

Clause X [iterator.concepts], paragraph 5, says that the only expression that is defined for a singular iterator is "an assignment of a non-singular value to an iterator that holds a singular value". This means that destroying a singular iterator (e.g. letting an automatic variable go out of scope) is technically undefined behavior. This seems overly strict, and probably unintentional.

Proposed resolution:

Change the sentence in question to "... the only exceptions are destroying an iterator that holds a singular value, or the assignment of a non-singular value to an iterator that holds a singular value."

### 409. Closing an fstream should clear error state

Section: 27.9.1.9 [ifstream.members], 27.9.1.13 [ofstream.members] Status: CD1 Submitter: Nathan Myers Opened: 2003-06-03 Last modified: 2009-05-01

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Discussion:

A strict reading of 27.9.1 [fstreams] shows that opening or closing a basic_[io]fstream does not affect the error bits. This means, for example, that if you read through a file up to EOF, and then close the stream and reopen it at the beginning of the file, the EOF bit in the stream's error state is still set. This is counterintuitive.

The LWG considered this issue once before, as issue 22, and put in a footnote to clarify that the strict reading was indeed correct. We did that because we believed the standard was unambiguous and consistent, and that we should not make architectural changes in a TC. Now that we're working on a new revision of the language, those considerations no longer apply.

Proposed resolution:

Change 27.9.1.9 [ifstream.members], para. 3 from:

> Calls rdbuf()->open(s,mode|in). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)].

to:

> Calls rdbuf()->open(s,mode|in). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)), else calls clear().

Change 27.9.1.13 [ofstream.members], para. 3 from:

> Calls rdbuf()->open(s,mode|out). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)).

to:

> Calls rdbuf()->open(s,mode|out). If that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure [Footnote: (lib.iostate.flags)), else calls clear().

Change 27.9.1.17 [fstream.members], para. 3 from:

> Calls rdbuf()->open(s,mode), If that function returns a null pointer, calls setstate(failbit), (which may throw ios_base::failure). (lib.iostate.flags) )

to:

> Calls rdbuf()->open(s,mode), If that function returns a null pointer, calls setstate(failbit), (which may throw ios_base::failure). (lib.iostate.flags) ), else calls clear().

[Kona: the LWG agrees this is a good idea. Post-Kona: Bill provided wording. He suggests having open, not close, clear the error flags.]

[Post-Sydney: Howard provided a new proposed resolution. The old one didn't make sense because it proposed to fix this at the level of basic_filebuf, which doesn't have access to the stream's error state. Howard's proposed resolution fixes this at the level of the three fstream class template instead.]

### 410. Missing semantics for stack and queue comparison operators

Section: 23.3.4.1 [list.cons], 23.3.4.3 [list.modifiers] Status: CD1 Submitter: Hans Bos Opened: 2003-06-07 Last modified: 2008-09-26

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Discussion:

Sections 23.3.4.1 [list.cons] and 23.3.4.3 [list.modifiers] list comparison operators (==, !=, <, <=, >, =>) for queue and stack. Only the semantics for queue::operator== (23.3.4.1 [list.cons] par2) and queue::operator< (23.3.4.1 [list.cons] par3) are defined.

Proposed resolution:

Add the following new paragraphs after 23.3.4.1 [list.cons] paragraph 3:

>       operator!=

> Returns: `x.c != y.c`

>       operator>

> Returns: `x.c > y.c`

>       operator<=

> Returns: `x.c <= y.c`

>       operator>=

> Returns: `x.c >= y.c`

Add the following paragraphs at the end of 23.3.4.3 [list.modifiers]:

>       operator==

> Returns: `x.c == y.c`

>       operator<

> Returns: `x.c < y.c`

>       operator!=

> Returns: `x.c != y.c`

>       operator>

> Returns: `x.c > y.c`

>       operator<=

> Returns: `x.c <= y.c`

>       operator>=

> Returns: `x.c >= y.c`

[Kona: Matt provided wording.]

Rationale:

There isn't any real doubt about what these operators are supposed to do, but we ought to spell it out.

### 411. Wrong names of set member functions

Section: 25.4.5 [alg.set.operations] Status: CD1 Submitter: Daniel Frey Opened: 2003-07-09 Last modified: 2008-09-26

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Discussion:

25.4.5 [alg.set.operations] paragraph 1 reads: "The semantics of the set operations are generalized to multisets in a standard way by defining union() to contain the maximum number of occurrences of every element, intersection() to contain the minimum, and so on."

This is wrong. The name of the functions are set_union() and set_intersection(), not union() and intersection().

Proposed resolution:

Change that sentence to use the correct names.

### 412. Typo in 27.4.4.3

Section: 27.5.4.3 [iostate.flags] Status: CD1 Submitter: Martin Sebor Opened: 2003-07-10 Last modified: 2008-09-26

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Duplicate of: 429

Discussion:

The Effects clause in 27.5.4.3 [iostate.flags] paragraph 5 says that the function only throws if the respective bits are already set prior to the function call. That's obviously not the intent. The typo ought to be corrected and the text reworded as: "If (state & exceptions()) == 0, returns. ..."

Proposed resolution:

In 27.5.4.3 [iostate.flags] paragraph 5, replace "If (rdstate() & exceptions()) == 0" with "If ((state | (rdbuf() ? goodbit : badbit)) & exceptions()) == 0".

[Kona: the original proposed resolution wasn't quite right. We really do mean rdstate(); the ambiguity is that the wording in the standard doesn't make it clear whether we mean rdstate() before setting the new state, or rdsate() after setting it. We intend the latter, of course. Post-Kona: Martin provided wording.]

### 413. Proposed resolution to LDR#64 still wrong

Section: 27.7.1.2.3 [istream::extractors] Status: CD1 Submitter: Bo Persson Opened: 2003-07-13 Last modified: 2009-05-01

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Discussion:

The second sentence of the proposed resolution says:

"If it inserted no characters because it caught an exception thrown while extracting characters from sb and ..."

However, we are not extracting from sb, but extracting from the basic_istream (*this) and inserting into sb. I can't really tell if "extracting" or "sb" is a typo.

[ Sydney: Definitely a real issue. We are, indeed, extracting characters from an istream and not from sb. The problem was there in the FDIS and wasn't fixed by issue 64. Probably what was intended was to have *this instead of sb. We're talking about the exception flag state of a basic_istream object, and there's only one basic_istream object in this discussion, so that would be a consistent interpretation. (But we need to be careful: the exception policy of this member function must be consistent with that of other extractors.) PJP will provide wording. ]

Proposed resolution:

Change the sentence from:

> If it inserted no characters because it caught an exception thrown while extracting characters from sb and failbit is on in exceptions(), then the caught exception is rethrown.

to:

> If it inserted no characters because it caught an exception thrown while extracting characters from *this and failbit is on in exceptions(), then the caught exception is rethrown.

### 414. Which iterators are invalidated by v.erase()?

Section: 23.3.6.4 [vector.modifiers] Status: CD1 Submitter: Matt Austern Opened: 2003-08-19 Last modified: 2008-09-26

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Discussion:

Consider the following code fragment:

>     int A[8] = { 1,3,5,7,9,8,4,2 };
>     std::vector<int> v(A, A+8);

>     std::vector<int>::iterator i1 = v.begin() + 3;
>     std::vector<int>::iterator i2 = v.begin() + 4;
>     v.erase(i1);

Which iterators are invalidated by `v.erase(i1)`: i1, i2, both, or neither?

On all existing implementations that I know of, the status of i1 and i2 is the same: both of them will be iterators that point to some elements of the vector (albeit not the same elements they did before). You won't get a crash if you use them. Depending on exactly what you mean by "invalidate", you might say that neither one has been invalidated because they still point to something, or you might say that both have been invalidated because in both cases the elements they point to have been changed out from under the iterator.

The standard doesn't say either of those things. It says that erase invalidates all iterators and references "after the point of the erase". This doesn't include i1, since it's at the point of the erase instead of after it. I can't think of any sensible definition of invalidation by which one can say that i2 is invalidated but i1 isn't.

(This issue is important if you try to reason about iterator validity based only on the guarantees in the standard, rather than reasoning from typical implementation techniques. Strict debugging modes, which some programmers find useful, do not use typical implementation techniques.)

Proposed resolution:

In 23.3.6.4 [vector.modifiers] paragraph 3, change "Invalidates all the iterators and references after the point of the erase" to "Invalidates iterators and references at or after the point of the erase".

Rationale:

I believe this was essentially a typographical error, and that it was taken for granted that erasing an element invalidates iterators that point to it. The effects clause in question treats iterators and references in parallel, and it would seem counterintuitive to say that a reference to an erased value remains valid.

### 415. behavior of std::ws

Section: 27.7.1.4 [istream.manip] Status: CD1 Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2008-09-26

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Discussion:

According to 27.6.1.4, the ws() manipulator is not required to construct the sentry object. The manipulator is also not a member function so the text in 27.6.1, p1 through 4 that describes the exception policy for istream member functions does not apply. That seems inconsistent with the rest of extractors and all the other input functions (i.e., ws will not cause a tied stream to be flushed before extraction, it doesn't check the stream's exceptions or catch exceptions thrown during input, and it doesn't affect the stream's gcount).

Proposed resolution:

Add to 27.7.1.4 [istream.manip], immediately before the first sentence of paragraph 1, the following text:

> Behaves as an unformatted input function (as described in 27.6.1.3, paragraph 1), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to is.gcount(). After constructing a sentry object...

[Post-Kona: Martin provided wording]

### 416. definitions of XXX_MIN and XXX_MAX macros in climits

Section: 18.3.2 [c.limits] Status: CD1 Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2008-09-26

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Discussion:

Given two overloads of the function foo(), one taking an argument of type int and the other taking a long, which one will the call foo(LONG_MAX) resolve to? The expected answer should be foo(long), but whether that is true depends on the #defintion of the LONG_MAX macro, specifically its type. This issue is about the fact that the type of these macros is not actually required to be the same as the the type each respective limit.
Section 18.2.2 of the C++ Standard does not specify the exact types of the XXX_MIN and XXX_MAX macros #defined in the <climits> and <limits.h> headers such as INT_MAX and LONG_MAX and instead defers to the C standard.
Section 5.2.4.2.1, p1 of the C standard specifies that "The values [of these constants] shall be replaced by constant expressions suitable for use in #if preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the following shall be replaced by expressions that have the same type as would an expression that is an object of the corresponding type converted according to the integer promotions."
The "corresponding type converted according to the integer promotions" for LONG_MAX is, according to 6.4.4.1, p5 of the C standard, the type of long converted to the first of the following set of types that can represent it: int, long int, long long int. So on an implementation where (sizeof(long) == sizeof(int)) this type is actually int, while on an implementation where (sizeof(long) > sizeof(int)) holds this type will be long.
This is not an issue in C since the type of the macro cannot be detected by any conforming C program, but it presents a portability problem in C++ where the actual type is easily detectable by overload resolution.

[Kona: the LWG does not believe this is a defect. The C macro definitions are what they are; we've got a better mechanism, `std::numeric_limits`, that is specified more precisely than the C limit macros. At most we should add a nonnormative note recommending that users who care about the exact types of limit quantities should use <limits> instead of <climits>.]

Proposed resolution:

Change 18.3.2 [c.limits], paragraph 2:

> -2- The contents are the same as the Standard C library header `<limits.h>`. [Note: The types of the macros in `<climits>` are not guaranteed to match the type to which they refer.--end note]

### 419. istream extractors not setting failbit if eofbit is already set

Section: 27.7.1.1.3 [istream::sentry] Status: WP Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2009-10-26

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Discussion:

27.7.1.1.3 [istream::sentry], p2 says that istream::sentry ctor prepares for input if is.good() is true. p4 then goes on to say that the ctor sets the sentry::ok_ member to true if the stream state is good after any preparation. 27.7.1.2.1 [istream.formatted.reqmts], p1 then says that a formatted input function endeavors to obtain the requested input if the sentry's operator bool() returns true. Given these requirements, no formatted extractor should ever set failbit if the initial stream rdstate() == eofbit. That is contrary to the behavior of all implementations I tested. The program below prints out eof = 1, fail = 0 eof = 1, fail = 1 on all of them.

    #include <sstream>
    #include <cstdio>

    int main()
    {
        std::istringstream strm ("1");

        int i = 0;

        strm >> i;

        std::printf ("eof = %d, fail = %d\n",
                     !!strm.eof (), !!strm.fail ());

        strm >> i;

        std::printf ("eof = %d, fail = %d\n",
                     !!strm.eof (), !!strm.fail ());
    }

Comments from Jerry Schwarz (c++std-lib-11373):
Jerry Schwarz wrote:
I don't know where (if anywhere) it says it in the standard, but the formatted extractors are supposed to set failbit if they don't extract any characters. If they didn't then simple loops like
while (cin >> x);
would loop forever.
Further comments from Martin Sebor:
The question is which part of the extraction should prevent this from happening by setting failbit when eofbit is already set. It could either be the sentry object or the extractor. It seems that most implementations have chosen to set failbit in the sentry [...] so that's the text that will need to be corrected.

Pre Berlin: This issue is related to 342. If the sentry sets `failbit` when it finds `eofbit` already set, then you can never seek away from the end of stream.

Kona: Possibly NAD. If eofbit is set then good() will return false. We then set ok to false. We believe that the sentry's constructor should always set failbit when ok is false, and we also think the standard already says that. Possibly it could be clearer.

[ 2009-07 Frankfurt ]

> Moved to Ready.

Proposed resolution:

Change 27.7.1.1.3 [istream::sentry], p2 to:

>     explicit sentry(basic_istream<charT,traits>& is , bool noskipws = false);

> -2- Effects: If `is.good()` is `true` `false`, calls `is.setstate(failbit)`. Otherwise prepares for formatted or unformatted input. ...

### 420. is std::FILE a complete type?

Section: 27.9.1 [fstreams] Status: CD1 Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2008-09-26

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Discussion:

7.19.1, p2, of C99 requires that the FILE type only be declared in <stdio.h>. None of the (implementation-defined) members of the struct is mentioned anywhere for obvious reasons.

C++ says in 27.8.1, p2 that FILE is a type that's defined in <cstdio>. Is it really the intent that FILE be a complete type or is an implementation allowed to just declare it without providing a full definition?

Proposed resolution:

In the first sentence of 27.9.1 [fstreams] paragraph 2, change "defined" to "declared".

Rationale:

We don't want to impose any restrictions beyond what the C standard already says. We don't want to make anything implementation defined, because that imposes new requirements in implementations.

### 422. explicit specializations of member functions of class templates

Section: 17.6.3.3 [reserved.names] Status: CD1 Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2008-09-26

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Discussion:

It has been suggested that 17.4.3.1, p1 may or may not allow programs to explicitly specialize members of standard templates on user-defined types. The answer to the question might have an impact where library requirements are given using the "as if" rule. I.e., if programs are allowed to specialize member functions they will be able to detect an implementation's strict conformance to Effects clauses that describe the behavior of the function in terms of the other member function (the one explicitly specialized by the program) by relying on the "as if" rule.

Proposed resolution:

Add the following sentence to 17.6.3.3 [reserved.names], p1:

> It is undefined for a C++ program to add declarations or definitions to namespace std or namespaces within namespace `std` unless otherwise specified. A program may add template specializations for any standard library template to namespace `std`. Such a specialization (complete or partial) of a standard library template results in undefined behavior unless the declaration depends on a user-defined type of external linkage and unless the specialization meets the standard library requirements for the original template.168) A program has undefined behavior if it declares

> - an explicit specialization of any member function of a standard library class template, or
> - an explicit specialization of any member function template of a standard library class or class template, or
> - an explicit or partial specialization of any member class template of a standard library class or class template.

> A program may explicitly instantiate any templates in the standard library only if the declaration depends on the name of a user-defined type of external linkage and the instantiation meets the standard library requirements for the original template.

[Kona: straw poll was 6-1 that user programs should not be allowed to specialize individual member functions of standard library class templates, and that doing so invokes undefined behavior. Post-Kona: Martin provided wording.]

[Sydney: The LWG agrees that the standard shouldn't permit users to specialize individual member functions unless they specialize the whole class, but we're not sure these words say what we want them to; they could be read as prohibiting the specialization of any standard library class templates. We need to consult with CWG to make sure we use the right wording.]

### 425. return value of std::get_temporary_buffer

Section: 20.8.11 [temporary.buffer] Status: CD1 Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2008-09-26

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Discussion:

The standard is not clear about the requirements on the value returned from a call to get_temporary_buffer(0). In particular, it fails to specify whether the call should return a distinct pointer each time it is called (like operator new), or whether the value is unspecified (as if returned by malloc). The standard also fails to mention what the required behavior is when the argument is less than 0.

Proposed resolution:

Change 20.6.3 [meta.help] paragraph 2 from "...or a pair of 0 values if no storage can be obtained" to "...or a pair of 0 values if no storage can be obtained or if n <= 0."

[Kona: Matt provided wording]

### 426. search_n(), fill_n(), and generate_n() with negative n

Section: 25.2.12 [alg.search], 25.3.6 [alg.fill], 25.3.7 [alg.generate] Status: CD1 Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2008-09-26

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Discussion:

The complexity requirements for these function templates are incorrect (or don't even make sense) for negative n:

25.1.9, p7 (search_n):
Complexity: At most (last1 - first1) * count applications of the corresponding predicate.

25.2.5, p3 (fill_n):
Complexity: Exactly last - first (or n) assignments.

25.2.6, p3 (generate_n):
Complexity: Exactly last - first (or n) assignments.

In addition, the Requirements or the Effects clauses for the latter two templates don't say anything about the behavior when n is negative.

Proposed resolution:

Change 25.1.9, p7 to

> Complexity: At most (last1 - first1) * count applications of the corresponding predicate if count is positive, or 0 otherwise.

Change 25.2.5, p2 to

> Effects: Assigns value through all the iterators in the range [first, last), or [first, first + n) if n is positive, none otherwise.

Change 25.2.5, p3 to:

> Complexity: Exactly last - first (or n if n is positive, or 0 otherwise) assignments.

Change 25.2.6, p1 to (notice the correction for the misspelled "through"):

> Effects: Invokes the function object genand assigns the return value of gen through all the iterators in the range [first, last), or [first, first + n) if n is positive, or [first, first) otherwise.

Change 25.2.6, p3 to:

> Complexity: Exactly last - first (or n if n is positive, or 0 otherwise) assignments.

Rationale:

Informally, we want to say that whenever we see a negative number we treat it the same as if it were zero. We believe the above changes do that (although they may not be the minimal way of saying so). The LWG considered and rejected the alternative of saying that negative numbers are undefined behavior.

### 428. string::erase(iterator) validity

Section: 21.4.6.5 [string::erase] Status: CD1 Submitter: Martin Sebor Opened: 2003-09-18 Last modified: 2008-09-26

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Discussion:

23.1.1, p3 along with Table 67 specify as a prerequisite for a.erase(q) that q must be a valid dereferenceable iterator into the sequence a.

However, 21.3.5.5, p5 describing string::erase(p) only requires that p be a valid iterator.

This may be interepreted as a relaxation of the general requirement, which is most likely not the intent.

Proposed resolution:

Remove 21.4.6.5 [string::erase] paragraph 5.

Rationale:

The LWG considered two options: changing the string requirements to match the general container requirements, or just removing the erroneous string requirements altogether. The LWG chose the latter option, on the grounds that duplicating text always risks the possibility that it might be duplicated incorrectly.

### 432. stringbuf::overflow() makes only one write position available

Section: 27.8.1.4 [stringbuf.virtuals] Status: CD1 Submitter: Christian W Brock Opened: 2003-09-24 Last modified: 2008-09-26

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Discussion:

27.7.1.3 par 8 says:

> Notes: The function can make a write position available only if ( mode & ios_base::out) != 0. To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus one additional write position. If ( mode & ios_base::in) != 0, the function alters the read end pointer egptr() to point just past the new write position (as does the write end pointer epptr()).

The sentences "plus one additional write position." and especially "(as does the write end pointer epptr())" COULD by interpreted (and is interpreted by at least my library vendor) as:

> post-condition: epptr() == pptr()+1

This WOULD force sputc() to call the virtual overflow() each time.

The proposed change also affects Defect Report 169.

Proposed resolution:

27.7.1.1/2 Change:

> 2- Notes: The function allocates no array object.

to:

> 2- Postcondition: str() == "".

27.7.1.1/3 Change:

> -3- Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() (lib.streambuf.cons), and initializing mode with which . Then copies the content of str into the basic_stringbuf underlying character sequence and initializes the input and output sequences according to which. If which & ios_base::out is true, initializes the output sequence with the underlying sequence. If which & ios_base::in is true, initializes the input sequence with the underlying sequence.

to:

> -3- Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() (lib.streambuf.cons), and initializing mode with which. Then copies the content of str into the basic_stringbuf underlying character sequence. If which & ios_base::out is true, initializes the output sequence such that pbase() points to the first underlying character, epptr() points one past the last underlying character, and if (which & ios_base::ate) is true, pptr() is set equal to epptr() else pptr() is set equal to pbase(). If which & ios_base::in is true, initializes the input sequence such that eback() and gptr() point to the first underlying character and egptr() points one past the last underlying character.

27.7.1.2/1 Change:

> -1- Returns: A basic_string object whose content is equal to the basic_stringbuf underlying character sequence. If the buffer is only created in input mode, the underlying character sequence is equal to the input sequence; otherwise, it is equal to the output sequence. In case of an empty underlying character sequence, the function returns basic_string<charT,traits,Allocator>().

to:

> -1- Returns: A basic_string object whose content is equal to the basic_stringbuf underlying character sequence. If the basic_stringbuf was created only in input mode, the resultant basic_string contains the character sequence in the range [eback(), egptr()). If the basic_stringbuf was created with (which & ios_base::out) being true then the resultant basic_string contains the character sequence in the range [pbase(), high_mark) where high_mark represents the position one past the highest initialized character in the buffer. Characters can be initialized either through writing to the stream, or by constructing the basic_stringbuf with a basic_string, or by calling the str(basic_string) member function. In the case of calling the str(basic_string) member function, all characters initialized prior to the call are now considered uninitialized (except for those characters re-initialized by the new basic_string). Otherwise the basic_stringbuf has been created in neither input nor output mode and a zero length basic_string is returned.

27.7.1.2/2 Change:

> -2- Effects: If the basic_stringbuf's underlying character sequence is not empty, deallocates it. Then copies the content of s into the basic_stringbuf underlying character sequence and initializes the input and output sequences according to the mode stored when creating the basic_stringbuf object. If (mode&ios_base::out) is true, then initializes the output sequence with the underlying sequence. If (mode&ios_base::in) is true, then initializes the input sequence with the underlying sequence.

to:

> -2- Effects: Copies the content of s into the basic_stringbuf underlying character sequence. If mode & ios_base::out is true, initializes the output sequence such that pbase() points to the first underlying character, epptr() points one past the last underlying character, and if (mode & ios_base::ate) is true, pptr() is set equal to epptr() else pptr() is set equal to pbase(). If mode & ios_base::in is true, initializes the input sequence such that eback() and gptr() point to the first underlying character and egptr() points one past the last underlying character.

Remove 27.2.1.2/3. (Same rationale as issue 238: incorrect and unnecessary.)

27.7.1.3/1 Change:

> 1- Returns: If the input sequence has a read position available, returns traits::to_int_type(*gptr()). Otherwise, returns traits::eof().

to:

> 1- Returns: If the input sequence has a read position available, returns traits::to_int_type(*gptr()). Otherwise, returns traits::eof(). Any character in the underlying buffer which has been initialized is considered to be part of the input sequence.

27.7.1.3/9 Change:

> -9- Notes: The function can make a write position available only if ( mode & ios_base::out) != 0. To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus one additional write position. If ( mode & ios_base::in) != 0, the function alters the read end pointer egptr() to point just past the new write position (as does the write end pointer epptr()).

to:

> -9- The function can make a write position available only if ( mode & ios_base::out) != 0. To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus one additional write position. If ( mode & ios_base::in) != 0, the function alters the read end pointer egptr() to point just past the new write position.

27.7.1.3/12 Change:

> -12- _ If (newoff + off) < 0, or (xend - xbeg) < (newoff + off), the positioning operation fails. Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext .

to:

> -12- _ If (newoff + off) < 0, or if (newoff + off) refers to an uninitialized character (as defined in 27.8.1.3 [stringbuf.members] paragraph 1), the positioning operation fails. Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext .

[post-Kona: Howard provided wording. At Kona the LWG agreed that something along these lines was a good idea, but the original proposed resolution didn't say enough about the effect of various member functions on the underlying character sequences.]

Rationale:

The current basic_stringbuf description is over-constrained in such a way as to prohibit vendors from making this the high-performance in-memory stream it was meant to be. The fundamental problem is that the pointers: eback(), gptr(), egptr(), pbase(), pptr(), epptr() are observable from a derived client, and the current description restricts the range [pbase(), epptr()) from being grown geometrically. This change allows, but does not require, geometric growth of this range.

Backwards compatibility issues: These changes will break code that derives from basic_stringbuf, observes epptr(), and depends upon [pbase(), epptr()) growing by one character on each call to overflow() (i.e. test suites). Otherwise there are no backwards compatibility issues.

27.7.1.1/2: The non-normative note is non-binding, and if it were binding, would be over specification. The recommended change focuses on the important observable fact.

27.7.1.1/3: This change does two things: 1. It describes exactly what must happen in terms of the sequences. The terms "input sequence" and "output sequence" are not well defined. 2. It introduces a common extension: open with app or ate mode. I concur with issue 238 that paragraph 4 is both wrong and unnecessary.

27.7.1.2/1: This change is the crux of the efficiency issue. The resultant basic_string is not dependent upon epptr(), and thus implementors are free to grow the underlying buffer geometrically during overflow() *and* place epptr() at the end of that buffer.

27.7.1.2/2: Made consistent with the proposed 27.7.1.1/3.

27.7.1.3/1: Clarifies that characters written to the stream beyond the initially specified string are available for reading in an i/o basic_streambuf.

27.7.1.3/9: Made normative by removing "Notes:", and removed the trailing parenthetical comment concerning epptr().

27.7.1.3/12: Restricting the positioning to [xbeg, xend) is no longer allowable since [pbase(), epptr()) may now contain uninitialized characters. Positioning is only allowable over the initialized range.

### 434. bitset::to_string() hard to use

Section: 20.3.7.2 [bitset.members] Status: CD1 Submitter: Martin Sebor Opened: 2003-10-15 Last modified: 2009-05-01

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Discussion:

It has been pointed out a number of times that the bitset to_string() member function template is tedious to use since callers must explicitly specify the entire template argument list (3 arguments). At least two implementations provide a number of overloads of this template to make it easier to use.

Proposed resolution:

In order to allow callers to specify no template arguments at all, just the first one (charT), or the first 2 (charT and traits), in addition to all three template arguments, add the following three overloads to both the interface (declarations only) of the class template bitset as well as to section 23.3.5.2, immediately after p34, the Returns clause of the existing to_string() member function template:

        template <class charT, class traits>
        basic_string<charT, traits, allocator<charT> >
        to_string () const;

        -34.1- Returns: to_string<charT, traits, allocator<charT> >().

        template <class charT>
        basic_string<charT, char_traits<charT>, allocator<charT> >
        to_string () const;

        -34.2- Returns: to_string<charT, char_traits<charT>, allocator<charT> >().

        basic_string<char, char_traits<char>, allocator<char> >
        to_string () const;

        -34.3- Returns: to_string<char, char_traits<char>, allocator<char> >().

[Kona: the LWG agrees that this is an improvement over the status quo. Dietmar thought about an alternative using a proxy object but now believes that the proposed resolution above is the right choice. ]

### 435. bug in DR 25

Section: 21.4.8.9 [string.io] Status: CD1 Submitter: Martin Sebor Opened: 2003-10-15 Last modified: 2008-09-26

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Discussion:

It has been pointed out that the proposed resolution in DR 25 may not be quite up to snuff:
http://gcc.gnu.org/ml/libstdc++/2003-09/msg00147.html http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#25

It looks like Petur is right. The complete corrected text is copied below. I think we may have have been confused by the reference to 22.2.2.2.2 and the subsequent description of `n' which actually talks about the second argument to sputn(), not about the number of fill characters to pad with.

So the question is: was the original text correct? If the intent was to follow classic iostreams then it most likely wasn't, since setting width() to less than the length of the string doesn't truncate it on output. This is also the behavior of most implementations (except for SGI's standard iostreams where the operator does truncate).

Proposed resolution:

Change the text in 21.3.7.9, p4 from

> If bool(k) is true, inserts characters as if by calling os.rdbuf()->sputn(str.data(), n), padding as described in stage 3 of lib.facet.num.put.virtuals, where n is the larger of os.width() and str.size();

to

> If bool(k) is true, determines padding as described in lib.facet.num.put.virtuals, and then inserts the resulting sequence of characters `seq` as if by calling `os.rdbuf()->sputn(seq, n)`, where `n` is the larger of `os.width()` and `str.size()`;

[Kona: it appears that neither the original wording, DR25, nor the proposed resolution, is quite what we want. We want to say that the string will be output, padded to os.width() if necessary. We don't want to duplicate the padding rules in clause 22, because they're complicated, but we need to be careful because they weren't quite written with quite this case in mind. We need to say what the character sequence is, and then defer to clause 22. Post-Kona: Benjamin provided wording.]

### 436. are cv-qualified facet types valid facets?

Section: 22.3.1.1.2 [locale.facet] Status: CD1 Submitter: Martin Sebor Opened: 2003-10-15 Last modified: 2008-09-26

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Discussion:

Is "const std::ctype<char>" a valid template argument to has_facet, use_facet, and the locale template ctor? And if so, does it designate the same Facet as the non-const "std::ctype<char>?" What about "volatile std::ctype<char>?" Different implementations behave differently: some fail to compile, others accept such types but behave inconsistently.

Proposed resolution:

Change 22.1.1.1.2, p1 to read:

Template parameters in this clause which are required to be facets are those named Facet in declarations. A program that passes a type that is not a facet, or a type that refers to volatile-qualified facet, as an (explicit or deduced) template parameter to a locale function expecting a facet, is ill-formed. A const-qualified facet is a valid template argument to any locale function that expects a Facet template parameter.

[Kona: changed the last sentence from a footnote to normative text.]

### 438. Ambiguity in the "do the right thing" clause

Section: 23.2.3 [sequence.reqmts] Status: CD1 Submitter: Howard Hinnant Opened: 2003-10-20 Last modified: 2009-05-01

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Discussion:

Section 23.2.3 [sequence.reqmts], paragraphs 9-11, fixed up the problem noticed with statements like:

    vector<int> v(10, 1);

The intent of the above statement was to construct with:

    vector(size_type, const value_type&);

but early implementations failed to compile as they bound to:

    template <class InputIterator>
    vector(InputIterator f, InputIterator l);

instead.

Paragraphs 9-11 say that if InputIterator is an integral type, then the member template constructor will have the same effect as:

    vector<static_cast<size_type>(f), static_cast<value_type>(l));

(and similarly for the other member template functions of sequences).

There is also a note that describes one implementation technique:

> One way that sequence implementors can satisfy this requirement is to specialize the member template for every integral type.

This might look something like:

>     template <class T>
>     struct vector
>     {
>          typedef unsigned size_type;

>          explicit vector(size_type) {}
>          vector(size_type, const T&) {}

>          template <class I>
>          vector(I, I);

>          // ...
>     };

>     template <class T>
>     template <class I>
>     vector<T>::vector(I, I) { ... }

>     template <>
>     template <>
>     vector<int>::vector(int, int) { ... }

>     template <>
>     template <>
>     vector<int>::vector(unsigned, unsigned) { ... }

>     //  ...

Label this solution 'A'.

The standard also says:

> Less cumbersome implementation techniques also exist.

A popular technique is to not specialize as above, but instead catch every call with the member template, detect the type of InputIterator, and then redirect to the correct logic. Something like:

>     template <class T>
>     template <class I>
>     vector<T>::vector(I f, I l)
>     {
>          choose_init(f, l, int2type<is_integral<I>::value>());
>     }

>     template <class T>
>     template <class I>
>     vector<T>::choose_init(I f, I l, int2type<false>)
>     {
>         // construct with iterators
>     }

>     template <class T>
>     template <class I>
>     vector<T>::choose_init(I f, I l, int2type<true>)
>     {
>         size_type sz = static_cast<size_type>(f);
>         value_type v = static_cast<value_type>(l);
>         // construct with sz,v
>     }

Label this solution 'B'.

Both of these solutions solve the case the standard specifically mentions:

    vector<int> v(10, 1);  // ok, vector size 10, initialized to 1

However, (and here is the problem), the two solutions have different behavior in some cases where the value_type of the sequence is not an integral type. For example consider:

>          pair<char, char>                     p('a', 'b');
>          vector<vector<pair<char, char> > >   d('a', 'b');

The second line of this snippet is likely an error. Solution A catches the error and refuses to compile. The reason is that there is no specialization of the member template constructor that looks like:

    template <>
    template <>
    vector<vector<pair<char, char> > >::vector(char, char) { ... }

So the expression binds to the unspecialized member template constructor, and then fails (compile time) because char is not an InputIterator.

Solution B compiles the above example though. 'a' is casted to an unsigned integral type and used to size the outer vector. 'b' is static casted to the inner vector using it's explicit constructor:

    explicit vector(size_type n);

and so you end up with a static_cast<size_type>('a') by static_cast<size_type>('b') matrix.

It is certainly possible that this is what the coder intended. But the explicit qualifier on the inner vector has been thwarted at any rate.

The standard is not clear whether the expression:

         vector<vector<pair<char, char> > >   d('a', 'b');

(and similar expressions) are:

1. undefined behavior.
2. illegal and must be rejected.
3. legal and must be accepted.

My preference is listed in the order presented.

There are still other techniques for implementing the requirements of paragraphs 9-11, namely the "restricted template technique" (e.g. enable_if). This technique is the most compact and easy way of coding the requirements, and has the behavior of #2 (rejects the above expression).

Choosing 1 would allow all implementation techniques I'm aware of. Choosing 2 would allow only solution 'A' and the enable_if technique. Choosing 3 would allow only solution 'B'.

Possible wording for a future standard if we wanted to actively reject the expression above would be to change "static_cast" in paragraphs 9-11 to "implicit_cast" where that is defined by:

>     template <class T, class U>
>     inline
>     T implicit_cast(const U& u)
>     {
>          return u;
>     }

Proposed resolution:

Replace 23.2.3 [sequence.reqmts] paragraphs 9 - 11 with:

For every sequence defined in this clause and in clause lib.strings:

- If the constructor

             template <class InputIterator>
             X(InputIterator f, InputIterator l,
               const allocator_type& a = allocator_type())

  is called with a type InputIterator that does not qualify as an input iterator, then the constructor will behave as if the overloaded constructor:

             X(size_type, const value_type& = value_type(),
               const allocator_type& = allocator_type())

  were called instead, with the arguments static_cast<size_type>(f), l and a, respectively.

- If the member functions of the forms:

             template <class InputIterator>          //  such as  insert()
             rt fx1(iterator p, InputIterator f, InputIterator l);

             template <class InputIterator>          //  such as  append(), assign()
             rt fx2(InputIterator f, InputIterator l);

             template <class InputIterator>          //  such as  replace()
             rt fx3(iterator i1, iterator i2, InputIterator f, InputIterator l);

  are called with a type InputIterator that does not qualify as an input iterator, then these functions will behave as if the overloaded member functions:

             rt fx1(iterator, size_type, const value_type&);

             rt fx2(size_type, const value_type&);

             rt fx3(iterator, iterator, size_type, const value_type&);

  were called instead, with the same arguments.

In the previous paragraph the alternative binding will fail if f is not implicitly convertible to X::size_type or if l is not implicitly convertible to X::value_type.

The extent to which an implementation determines that a type cannot be an input iterator is unspecified, except that as a minimum integral types shall not qualify as input iterators.

[ Kona: agreed that the current standard requires `v('a', 'b')` to be accepted, and also agreed that this is surprising behavior. The LWG considered several options, including something like implicit_cast, which doesn't appear to be quite what we want. We considered Howards three options: allow acceptance or rejection, require rejection as a compile time error, and require acceptance. By straw poll (1-6-1), we chose to require a compile time error. Post-Kona: Howard provided wording. ]

[ Sydney: The LWG agreed with this general direction, but there was some discomfort with the wording in the original proposed resolution. Howard submitted new wording, and we will review this again in Redmond. ]

[Redmond: one very small change in wording: the first argument is cast to size_t. This fixes the problem of something like `vector<vector<int> >(5, 5)`, where int is not implicitly convertible to the value type.]

Rationale:

The proposed resolution fixes:

      vector<int> v(10, 1);

since as integral types 10 and 1 must be disqualified as input iterators and therefore the (size,value) constructor is called (as if).

The proposed resolution breaks:

      vector<vector<T> > v(10, 1);

because the integral type 1 is not *implicitly* convertible to vector<T>. The wording above requires a diagnostic.

The proposed resolution leaves the behavior of the following code unspecified.

      struct A
      {
        operator int () const {return 10;}
      };

      struct B
      {
        B(A) {}
      };

      vector<B> v(A(), A());

The implementation may or may not detect that A is not an input iterator and employee the (size,value) constructor. Note though that in the above example if the B(A) constructor is qualified explicit, then the implementation must reject the constructor as A is no longer implicitly convertible to B.

### 441. Is fpos::state const?

Section: 27.5.3 [fpos] Status: CD1 Submitter: Vincent Leloup Opened: 2003-11-17 Last modified: 2008-09-26

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Discussion:

In section 27.5.3.1 [fpos.members] fpos<stateT>::state() is declared non const, but in section 27.5.3 [fpos] it is declared const.

Proposed resolution:

In section 27.5.3.1 [fpos.members], change the declaration of `fpos<stateT>::state()` to const.

### 442. sentry::operator bool() inconsistent signature

Section: 27.7.2.4 [ostream::sentry] Status: CD1 Submitter: Vincent Leloup Opened: 2003-11-18 Last modified: 2008-09-26

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Discussion:

In section 27.7.2.4 [ostream::sentry] paragraph 4, in description part basic_ostream<charT, traits>::sentry::operator bool() is declared as non const, but in section 27.6.2.3, in synopsis it is declared const.

Proposed resolution:

In section 27.7.2.4 [ostream::sentry] paragraph 4, change the declaration of `sentry::operator bool()` to const.

### 443. filebuf::close() inconsistent use of EOF

Section: 27.9.1.4 [filebuf.members] Status: CD1 Submitter: Vincent Leloup Opened: 2003-11-20 Last modified: 2008-09-26

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Discussion:

In section 27.9.1.4 [filebuf.members] par6, in effects description of basic_filebuf<charT, traits>::close(), overflow(EOF) is used twice; should be overflow(traits::eof()).

Proposed resolution:

Change overflow(EOF) to overflow(traits::eof()).

### 444. Bad use of casts in fstream

Section: 27.9.1 [fstreams] Status: CD1 Submitter: Vincent Leloup Opened: 2003-11-20 Last modified: 2009-05-01

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Discussion:

27.9.1.9 [ifstream.members] p1, 27.9.1.13 [ofstream.members] p1, 27.9.1.17 [fstream.members] p1 seems have same problem as exposed in LWG issue 252.

Proposed resolution:

[Sydney: Genuine defect. 27.8.1.13 needs a cast to cast away constness. The other two places are stylistic: we could change the C-style casts to const_cast. Post-Sydney: Howard provided wording. ]

Change 27.8.1.7/1 from:

> Returns: (basic_filebuf<charT,traits>*)&sb.

to:

> Returns: const_cast<basic_filebuf<charT,traits>*>(&sb).

Change 27.8.1.10/1 from:

> Returns: (basic_filebuf<charT,traits>*)&sb.

to:

> Returns: const_cast<basic_filebuf<charT,traits>*>(&sb).

Change 27.8.1.13/1 from:

> Returns: &sb.

to:

> Returns: const_cast<basic_filebuf<charT,traits>*>(&sb).

### 445. iterator_traits::reference unspecified for some iterator categories

Section: 24.4.1 [iterator.traits] Status: CD1 Submitter: Dave Abrahams Opened: 2003-12-09 Last modified: 2009-05-01

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Discussion:

The standard places no restrictions at all on the reference type of input, output, or forward iterators (for forward iterators it only specifies that *x must be value_type& and doesn't mention the reference type). Bidirectional iterators' reference type is restricted only by implication, since the base iterator's reference type is used as the return type of reverse_iterator's operator*, which must be T& in order to be a conforming forward iterator.

Here's what I think we ought to be able to expect from an input or forward iterator's reference type R, where a is an iterator and V is its value_type

- *a is convertible to R
- R is convertible to V
- static_cast<V>(static_cast<R>(*a)) is equivalent to static_cast<V>(*a)

A mutable forward iterator ought to satisfy, for x of type V:

          { R r = *a; r = x; } is equivalent to *a = x;

I think these requirements capture existing container iterators (including vector<bool>'s), but render istream_iterator invalid; its reference type would have to be changed to a constant reference.

(Jeremy Siek) During the discussion in Sydney, it was felt that a simpler long term solution for this was needed. The solution proposed was to require `reference` to be the same type as `*a` and `pointer` to be the same type as `a->`. Most iterators in the Standard Library already meet this requirement. Some iterators are output iterators, and do not need to meet the requirement, and others are only specified through the general iterator requirements (which will change with this resolution). The sole case where there is an explicit definition of the reference type that will need to change is `istreambuf_iterator` which returns `charT` from `operator*` but has a reference type of `charT&`. We propose changing the reference type of `istreambuf_iterator` to `charT`.

The other option for resolving the issue with `pointer`, mentioned in the note below, is to remove `pointer` altogether. I prefer placing requirements on `pointer` to removing it for two reasons. First, `pointer` will become useful for implementing iterator adaptors and in particular, `reverse_iterator` will become more well defined. Second, removing `pointer` is a rather drastic and publicly-visible action to take.

The proposed resolution technically enlarges the requirements for iterators, which means there are existing iterators (such as `istreambuf_iterator`, and potentially some programmer-defined iterators) that will no longer meet the requirements. Will this break existing code? The scenario in which it would is if an algorithm implementation (say in the Standard Library) is changed to rely on `iterator_traits::reference`, and then is used with one of the iterators that do not have an appropriately defined `iterator_traits::reference`.

The proposed resolution makes one other subtle change. Previously, it was required that output iterators have a `difference_type` and `value_type` of `void`, which means that a forward iterator could not be an output iterator. This is clearly a mistake, so I've changed the wording to say that those types may be `void`.

Proposed resolution:

In 24.4.1 [iterator.traits], after:

> be defined as the iterator's difference type, value type and iterator category, respectively.

add

> In addition, the types

>     iterator_traits<Iterator>::reference
>     iterator_traits<Iterator>::pointer

> must be defined as the iterator's reference and pointer types, that is, the same type as the type of `*a` and `a->`, respectively.

In 24.4.1 [iterator.traits], change:

> In the case of an output iterator, the types

>     iterator_traits<Iterator>::difference_type
>     iterator_traits<Iterator>::value_type

> are both defined as `void`.

to:

> In the case of an output iterator, the types

>     iterator_traits<Iterator>::difference_type
>     iterator_traits<Iterator>::value_type
>     iterator_traits<Iterator>::reference
>     iterator_traits<Iterator>::pointer

> may be defined as `void`.

In 24.6.3 [istreambuf.iterator], change:

>     typename traits::off_type, charT*, charT&>

to:

>     typename traits::off_type, charT*, charT>

[ Redmond: there was concern in Sydney that this might not be the only place where things were underspecified and needed to be changed. Jeremy reviewed iterators in the standard and confirmed that nothing else needed to be changed. ]

### 448. Random Access Iterators over abstract classes

Section: 24.2.5 [random.access.iterators] Status: CD1 Submitter: Dave Abrahams Opened: 2004-01-07 Last modified: 2008-09-26

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Discussion:

Table 76, the random access iterator requirement table, says that the return type of a[n] must be "convertible to T". When an iterator's value_type T is an abstract class, nothing is convertible to T. Surely this isn't an intended restriction?

Proposed resolution:

Change the return type to "convertible to T const&".

### 449. Library Issue 306 Goes Too Far

Section: 18.2 [support.types] Status: CD1 Submitter: Pete Becker Opened: 2004-01-15 Last modified: 2008-09-26

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Discussion:

Original text:

> The macro offsetof accepts a restricted set of type arguments in this International Standard. type shall be a POD structure or a POD union (clause 9). The result of applying the offsetof macro to a field that is a static data member or a function member is undefined."

Revised text:

> "If type is not a POD structure or a POD union the results are undefined."

Looks to me like the revised text should have replaced only the second sentence. It doesn't make sense standing alone.

Proposed resolution:

Change 18.1, paragraph 5, to:

> The macro offsetof accepts a restricted set of type arguments in this International Standard. If type is not a POD structure or a POD union the results are undefined. The result of applying the offsetof macro to a field that is a static data member or a function member is undefined."

### 453. basic_stringbuf::seekoff need not always fail for an empty stream

Section: 27.8.1.4 [stringbuf.virtuals] Status: CD1 Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2008-09-26

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Discussion:

      pos_type basic_stringbuf::seekoff(off_type, ios_base::seekdir,
                                        ios_base::openmode);

is obliged to fail if nothing has been inserted into the stream. This is unnecessary and undesirable. It should be permissible to seek to an effective offset of zero.

[ Sydney: Agreed that this is an annoying problem: seeking to zero should be legal. Bill will provide wording. ]

Proposed resolution:

Change the sentence from:

> For a sequence to be positioned, if its next pointer (either gptr() or pptr()) is a null pointer, the positioning operation fails.

to:

> For a sequence to be positioned, if its next pointer (either gptr() or pptr()) is a null pointer and the new offset newoff is nonzero, the positioning operation fails.

### 455. cerr::tie() and wcerr::tie() are overspecified

Section: 27.4 [iostream.objects] Status: CD1 Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2009-05-01

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Discussion:

Both cerr::tie() and wcerr::tie() are obliged to be null at program startup. This is overspecification and overkill. It is both traditional and useful to tie cerr to cout, to ensure that standard output is drained whenever an error message is written. This behavior should at least be permitted if not required. Same for wcerr::tie().

Proposed resolution:

Add to the description of cerr:

> After the object cerr is initialized, cerr.tie() returns &cout. Its state is otherwise the same as required for basic_ios<char>::init (lib.basic.ios.cons).

Add to the description of wcerr:

> After the object wcerr is initialized, wcerr.tie() returns &wcout. Its state is otherwise the same as required for basic_ios<wchar_t>::init (lib.basic.ios.cons).

[Sydney: straw poll (3-1): we should require, not just permit, cout and cerr to be tied on startup. Pre-Redmond: Bill will provide wording.]

### 456. Traditional C header files are overspecified

Section: 17.6.1.2 [headers] Status: CD1 Submitter: Bill Plauger Opened: 2004-01-30 Last modified: 2008-09-26

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Discussion:

The C++ Standard effectively requires that the traditional C headers (of the form <xxx.h>) be defined in terms of the newer C++ headers (of the form <cxxx>). Clauses 17.4.1.2/4 and D.5 combine to require that:

- Including the header <cxxx> declares a C name in namespace std.
- Including the header <xxx.h> declares a C name in namespace std (effectively by including <cxxx>), then imports it into the global namespace with an individual using declaration.

The rules were left in this form despited repeated and heated objections from several compiler vendors. The C headers are often beyond the direct control of C++ implementors. In some organizations, it's all they can do to get a few #ifdef __cplusplus tests added. Third-party library vendors can perhaps wrap the C headers. But neither of these approaches supports the drastic restructuring required by the C++ Standard. As a result, it is still widespread practice to ignore this conformance requirement, nearly seven years after the committee last debated this topic. Instead, what is often implemented is:

- Including the header <xxx.h> declares a C name in the global namespace.
- Including the header <cxxx> declares a C name in the global namespace (effectively by including <xxx.h>), then imports it into namespace std with an individual using declaration.

The practical benefit for implementors with the second approach is that they can use existing C library headers, as they are pretty much obliged to do. The practical cost for programmers facing a mix of implementations is that they have to assume weaker rules:

- If you want to assuredly declare a C name in the global namespace, include <xxx.h>. You may or may not also get the declaration in namespace std.
- If you want to assuredly declare a C name in namespace std, include <cxxx>. You may or may not also get the declaration in the global namespace.

There also exists the possibility of subtle differences due to Koenig lookup, but there are so few non-builtin types defined in the C headers that I've yet to see an example of any real problems in this area.

It is worth observing that the rate at which programmers fall afoul of these differences has remained small, at least as measured by newsgroup postings and our own bug reports. (By an overwhelming margin, the commonest problem is still that programmers include <string> and can't understand why the typename string isn't defined -- this a decade after the committee invented namespace std, nominally for the benefit of all programmers.)

We should accept the fact that we made a serious mistake and rectify it, however belatedly, by explicitly allowing either of the two schemes for declaring C names in headers.

[Sydney: This issue has been debated many times, and will certainly have to be discussed in full committee before any action can be taken. However, the preliminary sentiment of the LWG was in favor of the change. (6 yes, 0 no, 2 abstain) Robert Klarer suggests that we might also want to undeprecate the C-style `.h` headers.]

Proposed resolution:

Add to 17.6.1.2 [headers], para. 4:

> Except as noted in clauses 18 through 27 and Annex D, the contents of each header cname shall be the same as that of the corresponding header name.h, as specified in ISO/IEC 9899:1990 Programming Languages C (Clause 7), or ISO/IEC:1990 Programming Languages-C AMENDMENT 1: C Integrity, (Clause 7), as appropriate, as if by inclusion. In the C++ Standard Library, however, the declarations and definitions (except for names which are defined as macros in C) are within namespace scope (3.3.5) of the namespace std. It is unspecified whether these names are first declared within the global namespace scope and are then injected into namespace std by explicit using-declarations (7.3.3 [namespace.udecl]).

Change D.6 [depr.c.headers], para. 2-3:

> -2- Every C header, each of which has a name of the form name.h, behaves as if each name placed in the Standard library namespace by the corresponding cname header is also placed within the global namespace scope. of the namespace `std` and is followed by an explicit using-declaration (7.3.3 [namespace.udecl]). It is unspecified whether these names are first declared or defined within namespace scope (3.3.6 [basic.scope.namespace]) of the namespace `std` and are then injected into the global namespace scope by explicit using-declarations (7.3.3 [namespace.udecl]).

> -3- [Example: The header `<cstdlib>` assuredly provides its declarations and definitions within the namespace `std`. It may also provide these names within the global namespace. The header `<stdlib.h>` makes these available also in assuredly provides the same declarations and definitions within the global namespace, much as in the C Standard. It may also provide these names within the namespace `std`. -- end example]

### 457. bitset constructor: incorrect number of initialized bits

Section: 20.3.7.1 [bitset.cons] Status: CD1 Submitter: Dag Henriksson Opened: 2004-01-30 Last modified: 2009-05-01

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Discussion:

The constructor from unsigned long says it initializes "the first M bit positions to the corresponding bit values in val. M is the smaller of N and the value CHAR_BIT * sizeof(unsigned long)."

Object-representation vs. value-representation strikes again. CHAR_BIT * sizeof (unsigned long) does not give us the number of bits an unsigned long uses to hold the value. Thus, the first M bit position above is not guaranteed to have any corresponding bit values in val.

Proposed resolution:

In 20.3.7.1 [bitset.cons] paragraph 2, change "M is the smaller of N and the value CHAR_BIT * sizeof (unsigned long). (249)" to "`M` is the smaller of `N` and the number of bits in the value representation (section 3.9 [basic.types]) of `unsigned long`."

### 460. Default modes missing from basic_fstream member specifications

Section: 27.9.1 [fstreams] Status: CD1 Submitter: Ben Hutchings Opened: 2004-04-01 Last modified: 2009-05-01

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Discussion:

The second parameters of the non-default constructor and of the open member function for basic_fstream, named "mode", are optional according to the class declaration in 27.8.1.11 [lib.fstream]. The specifications of these members in 27.8.1.12 [lib.fstream.cons] and 27.8.1.13 lib.fstream.members] disagree with this, though the constructor declaration has the "explicit" function-specifier implying that it is intended to be callable with one argument.

Proposed resolution:

In 27.9.1.15 [fstream.cons], change

      explicit basic_fstream(const char* s, ios_base::openmode mode);

to

      explicit basic_fstream(const char* s,
                             ios_base::openmode mode = ios_base::in|ios_base::out);

In 27.9.1.17 [fstream.members], change

      void open(const char*s, ios_base::openmode mode);

to

      void open(const char*s,
                ios_base::openmode mode = ios_base::in|ios_base::out);

### 461. time_get hard or impossible to implement

Section: 22.4.5.1.2 [locale.time.get.virtuals] Status: CD1 Submitter: Bill Plauger Opened: 2004-03-23 Last modified: 2008-09-26

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Discussion:

Template time_get currently contains difficult, if not impossible, requirements for do_date_order, do_get_time, and do_get_date. All require the implementation to scan a field generated by the %x or %X conversion specifier in strftime. Yes, do_date_order can always return no_order, but that doesn't help the other functions. The problem is that %x can be nearly anything, and it can vary widely with locales. It's horribly onerous to have to parse "third sunday after Michaelmas in the year of our Lord two thousand and three," but that's what we currently ask of do_get_date. More practically, it leads some people to think that if %x produces 10.2.04, we should know to look for dots as separators. Still not easy.

Note that this is the opposite effect from the intent stated in the footnote earlier in this subclause:

> "In other words, user confirmation is required for reliable parsing of user-entered dates and times, but machine-generated formats can be parsed reliably. This allows parsers to be aggressive about interpreting user variations on standard formats."

We should give both implementers and users an easier and more reliable alternative: provide a (short) list of alternative delimiters and say what the default date order is for no_order. For backward compatibility, and maximum latitude, we can permit an implementation to parse whatever %x or %X generates, but we shouldn't require it.

Proposed resolution:

In the description:

    iter_type do_get_time(iter_type s, iter_type end, ios_base& str,
            ios_base::iostate& err, tm* t) const;

2 Effects: Reads characters starting at suntil it has extracted those struct tm members, and remaining format characters, used by time_put<>::put to produce the format specified by 'X', or until it encounters an error or end of sequence.

change: 'X'

to: "%H:%M:%S"

Change

    iter_type do_get_date(iter_type s, iter_type end, ios_base& str,
            ios_base::iostate& err, tm* t) const;

    4 Effects: Reads characters starting at s until it has extracted those
    struct tm members, and remaining format characters, used by
    time_put<>::put to produce the format specified by 'x', or until it
    encounters an error.

to

    iter_type do_get_date(iter_type s, iter_type end, ios_base& str,
            ios_base::iostate& err, tm* t) const;

4 Effects: Reads characters starting at s until it has extracted those struct tm members, and remaining format characters, used by time_put<>::put to produce one of the following formats, or until it encounters an error. The format depends on the value returned by date_order() as follows:

            date_order()  format

            no_order      "%m/%d/%y"
            dmy           "%d/%m/%y"
            mdy           "%m/%d/%y"
            ymd           "%y/%m/%d"
            ydm           "%y/%d/%m"

An implementation may also accept additional implementation-defined formats.

[Redmond: agreed that this is a real problem. The solution is probably to match C99's parsing rules. Bill provided wording. ]

### 464. Suggestion for new member functions in standard containers

Section: 23.3.6 [vector], 23.4.1 [map] Status: CD1 Submitter: Thorsten Ottosen Opened: 2004-05-12 Last modified: 2008-09-26

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Discussion:

To add slightly more convenience to vector<T> and map<Key,T> we should consider to add

1. add vector<T>::data() member (const and non-const version) semantics: if( empty() ) return 0; else return buffer_;
2. add map<Key,T>::at( const Key& k ) member (const and non-const version) semantics: iterator i = find( k ); if( i != end() ) return *i; else throw range_error();

Rationale:

- To obtain a pointer to the vector's buffer, one must use either operator[]() (which can give undefined behavior for empty vectors) or at() (which will then throw if the vector is empty).
- tr1::array<T,sz> already has a data() member
- e cannot use operator[]() when T is not DefaultDonstructible
- Neither when the map is const.
- when we want to make sure we don't add an element accidently
- when it should be considered an error if a key is not in the map

Proposed resolution:

In 23.3.6 [vector], add the following to the `vector` synopsis after "element access" and before "modifiers":

      // [lib.vector.data] data access
      pointer       data();
      const_pointer data() const;

Add a new subsection of 23.3.6 [vector]:

> 23.2.4.x `vector` data access

>        pointer       data();
>        const_pointer data() const;

> Returns: A pointer such that [data(), data() + size()) is a valid range. For a non-empty vector, data() == &front().

> Complexity: Constant time.

> Throws: Nothing.

In 23.4.1 [map], add the following to the `map` synopsis immediately after the line for operator[]:

      T&       at(const key_type& x);
      const T& at(const key_type& x) const;

Add the following to 23.4.1.2 [map.access]:

>       T&       at(const key_type& x);
>       const T& at(const key_type& x) const;

> Returns: A reference to the element whose key is equivalent to x, if such an element is present in the map.

> Throws: `out_of_range` if no such element is present.

Rationale:

Neither of these additions provides any new functionality but the LWG agreed that they are convenient, especially for novices. The exception type chosen for `at`, `std::out_of_range`, was chosen to match `vector::at`.

### 465. Contents of <ciso646>

Section: 17.6.1.2 [headers] Status: CD1 Submitter: Steve Clamage Opened: 2004-06-03 Last modified: 2008-09-26

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Discussion:

C header <iso646.h> defines macros for some operators, such as not_eq for !=.

Section 17.6.1.2 [headers] "Headers" says that except as noted in clauses 18 through 27, the <cname> C++ header contents are the same as the C header <name.h>. In particular, table 12 lists <ciso646> as a C++ header.

I don't find any other mention of <ciso646>, or any mention of <iso646.h>, in clauses 17 thorough 27. That implies that the contents of <ciso646> are the same as C header <iso646.h>.

Annex C (informative, not normative) in [diff.header.iso646.h] C.2.2.2 "Header <iso646.h>" says that the alternative tokens are not defined as macros in <ciso646>, but does not mention the contents of <iso646.h>.

I don't find any normative text to support C.2.2.2.

Proposed resolution:

Add to section 17.4.1.2 Headers [lib.headers] a new paragraph after paragraph 6 (the one about functions must be functions):

> Identifiers that are keywords or operators in C++ shall not be defined as macros in C++ standard library headers. [Footnote:In particular, including the standard header <iso646.h> or <ciso646> has no effect.

[post-Redmond: Steve provided wording.]

### 467. char_traits::lt(), compare(), and memcmp()

Section: 21.2.3.1 [char.traits.specializations.char] Status: CD1 Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2008-09-26

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Discussion:

Table 37 describes the requirements on Traits::compare() in terms of those on Traits::lt(). 21.1.3.1, p6 requires char_traits<char>::lt() to yield the same result as operator<(char, char).

Most, if not all, implementations of char_traits<char>::compare() call memcmp() for efficiency. However, the C standard requires both memcmp() and strcmp() to interpret characters under comparison as unsigned, regardless of the signedness of char. As a result, all these char_traits implementations fail to meet the requirement imposed by Table 37 on compare() when char is signed.

Read email thread starting with c++std-lib-13499 for more.

Proposed resolution:

Change 21.1.3.1, p6 from

> The two-argument members assign, eq, and lt are defined identically to the built-in operators =, ==, and < respectively.

to

> The two-argument member assign is defined identically to the built-in operator =. The two argument members eq and lt are defined identically to the built-in operators == and < for type unsigned char.

[Redmond: The LWG agreed with this general direction, but we also need to change `eq` to be consistent with this change. Post-Redmond: Martin provided wording.]

### 468. unexpected consequences of ios_base::operator void*()

Section: 27.5.4.3 [iostate.flags] Status: CD1 Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2008-09-26

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Discussion:

The program below is required to compile but when run it typically produces unexpected results due to the user-defined conversion from std::cout or any object derived from basic_ios to void*.

        #include <cassert>
        #include <iostream>

        int main ()
        {
            assert (std::cin.tie () == std::cout);
            // calls std::cout.ios::operator void*()
        }

Proposed resolution:

Replace std::basic_ios<charT, traits>::operator void*() with another conversion operator to some unspecified type that is guaranteed not to be convertible to any other type except for bool (a pointer-to-member might be one such suitable type). In addition, make it clear that the pointer type need not be a pointer to a complete type and when non-null, the value need not be valid.

Specifically, change in [lib.ios] the signature of

        operator void*() const;

to

        operator unspecified-bool-type() const;

and change [lib.iostate.flags], p1 from

        operator void*() const;

to

    operator unspecified-bool-type() const;

         -1- Returns: if fail() then a value that will evaluate false in a
          boolean context; otherwise a value that will evaluate true in a
          boolean context. The value type returned shall not be
          convertible to int.

         -2- [Note: This conversion can be used in contexts where a bool
          is expected (e.g., an if condition); however, implicit
          conversions (e.g., to int) that can occur with bool are not
          allowed, eliminating some sources of user error. One possible
          implementation choice for this type is pointer-to-member.  - end
          note]

[Redmond: 5-4 straw poll in favor of doing this.]

[Lillehammer: Doug provided revised wording for "unspecified-bool-type".]

### 469. vector<bool> ill-formed relational operators

Section: 23.3.6 [vector] Status: CD1 Submitter: Martin Sebor Opened: 2004-06-28 Last modified: 2009-05-01

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Discussion:

The overloads of relational operators for vector<bool> specified in [lib.vector.bool] are redundant (they are semantically identical to those provided for the vector primary template) and may even be diagnosed as ill-formed (refer to Daveed Vandevoorde's explanation in c++std-lib-13647).

Proposed resolution:

Remove all overloads of overloads of relational operators for vector<bool> from [lib.vector.bool].

### 474. confusing Footnote 297

Section: 27.7.2.6.4 [ostream.inserters.character] Status: CD1 Submitter: Martin Sebor Opened: 2004-07-01 Last modified: 2008-09-26

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Discussion:

I think Footnote 297 is confused. The paragraph it applies to seems quite clear in that widen() is only called if the object is not a char stream (i.e., not basic_ostream<char>), so it's irrelevant what the value of widen(c) is otherwise.

Proposed resolution:

I propose to strike the Footnote.

### 475. May the function object passed to for_each modify the elements of the iterated sequence?

Section: 25.2.4 [alg.foreach] Status: CD1 Submitter: Stephan T. Lavavej, Jaakko Jarvi Opened: 2004-07-09 Last modified: 2008-09-26

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Discussion:

It is not clear whether the function object passed to for_each is allowed to modify the elements of the sequence being iterated over.

for_each is classified without explanation in [lib.alg.nonmodifying], "25.1 Non-modifying sequence operations". 'Non-modifying sequence operation' is never defined.

25(5) says: "If an algorithm's Effects section says that a value pointed to by any iterator passed as an argument is modified, then that algorithm has an additional type requirement: The type of that argument shall satisfy the requirements of a mutable iterator (24.1)."

for_each's Effects section does not mention whether arguments can be modified:

> "Effects: Applies f to the result of dereferencing every iterator in the range [first, last), starting from first and proceeding to last - 1."

Every other algorithm in [lib.alg.nonmodifying] is "really" non-modifying in the sense that neither the algorithms themselves nor the function objects passed to the algorithms may modify the sequences or elements in any way. This DR affects only for_each.

We suspect that for_each's classification in "non-modifying sequence operations" means that the algorithm itself does not inherently modify the sequence or the elements in the sequence, but that the function object passed to it may modify the elements it operates on.

The original STL document by Stepanov and Lee explicitly prohibited the function object from modifying its argument. The "obvious" implementation of for_each found in several standard library implementations, however, does not impose this restriction. As a result, we suspect that the use of for_each with function objects that modify their arguments is wide-spread. If the restriction was reinstated, all such code would become non-conforming. Further, none of the other algorithms in the Standard could serve the purpose of for_each (transform does not guarantee the order in which its function object is called).

We suggest that the standard be clarified to explicitly allow the function object passed to for_each modify its argument.

Proposed resolution:

Add a nonnormative note to the Effects in 25.2.4 [alg.foreach]: If the type of 'first' satisfies the requirements of a mutable iterator, 'f' may apply nonconstant functions through the dereferenced iterators passed to it.

Rationale:

The LWG believes that nothing in the standard prohibits function objects that modify the sequence elements. The problem is that for_each is in a secion entitled "nonmutating algorithms", and the title may be confusing. A nonnormative note should clarify that.

### 478. Should forward iterator requirements table have a line for r->m?

Section: 24.2.3 [forward.iterators] Status: CD1 Submitter: Dave Abrahams Opened: 2004-07-11 Last modified: 2008-09-26

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Duplicate of: 477

Discussion:

The Forward Iterator requirements table contains the following:

     expression  return type         operational  precondition
                                      semantics
      ==========  ==================  ===========  ==========================
      a->m        U& if X is mutable, (*a).m       pre: (*a).m is well-defined.
                  otherwise const U&

      r->m        U&                  (*r).m       pre: (*r).m is well-defined.

The second line may be unnecessary. Paragraph 11 of [lib.iterator.requirements] says:

> In the following sections, a and b denote values of type const X, n denotes a value of the difference type Distance, u, tmp, and m denote identifiers, r denotes a value of X&, t denotes a value of value type T, o denotes a value of some type that is writable to the output iterator.

Because operators can be overloaded on an iterator's const-ness, the current requirements allow iterators to make many of the operations specified using the identifiers a and b invalid for non-const iterators.

Related issue: 477

Proposed resolution:

Remove the "r->m" line from the Forward Iterator requirements table. Change

> "const X"

to

> "X or const X"

in paragraph 11 of [lib.iterator.requirements].

Rationale:

This is a defect because it constrains an lvalue to returning a modifiable lvalue.

### 488. rotate throws away useful information

Section: 25.3.11 [alg.rotate] Status: CD1 Submitter: Howard Hinnant Opened: 2004-11-22 Last modified: 2008-09-26

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Discussion:

rotate takes 3 iterators: first, middle and last which point into a sequence, and rearranges the sequence such that the subrange [middle, last) is now at the beginning of the sequence and the subrange [first, middle) follows. The return type is void.

In many use cases of rotate, the client needs to know where the subrange [first, middle) starts after the rotate is performed. This might look like:

      rotate(first, middle, last);
      Iterator i = advance(first, distance(middle, last));

Unless the iterators are random access, the computation to find the start of the subrange [first, middle) has linear complexity. However, it is not difficult for rotate to return this information with negligible additional computation expense. So the client could code:

      Iterator i = rotate(first, middle, last);

and the resulting program becomes significantly more efficient.

While the backwards compatibility hit with this change is not zero, it is very small (similar to that of lwg 130), and there is a significant benefit to the change.

Proposed resolution:

In 25 [algorithms] p2, change:

>       template<class ForwardIterator>
>         void ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
>                     ForwardIterator last);

In 25.3.11 [alg.rotate], change:

>       template<class ForwardIterator>
>         void ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
>                     ForwardIterator last);

In 25.3.11 [alg.rotate] insert a new paragraph after p1:

> Returns: `first + (last - middle)`.

[ The LWG agrees with this idea, but has one quibble: we want to make sure not to give the impression that the function "advance" is actually called, just that the nth iterator is returned. (Calling advance is observable behavior, since users can specialize it for their own iterators.) Howard will provide wording. ]

[Howard provided wording for mid-meeting-mailing Jun. 2005.]

[ Toronto: moved to Ready. ]

### 495. Clause 22 template parameter requirements

Section: 22 [localization] Status: CD1 Submitter: Beman Dawes Opened: 2005-01-10 Last modified: 2008-09-26

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Discussion:

It appears that there are no requirements specified for many of the template parameters in clause 22. It looks like this issue has never come up, except perhaps for Facet.

Clause 22 isn't even listed in 17.3.2.1 [lib.type.descriptions], either, which is the wording that allows requirements on template parameters to be identified by name.

So one issue is that 17.3.2.1 [lib.type.descriptions] Should be changed to cover clause 22. A better change, which will cover us in the future, would be to say that it applies to all the library clauses. Then if a template gets added to any library clause we are covered.

charT, InputIterator, and other names with requirements defined elsewhere are fine, assuming the 17.3.2.1 [lib.type.descriptions] fix. But there are a few template arguments names which I don't think have requirements given elsewhere:

- internT and externT. The fix is to add wording saying that internT and externT must meet the same requirements as template arguments named charT.
- stateT. I'm not sure about this one. There already is some wording, but it seems a bit vague.
- Intl. [lib.locale.moneypunct.byname] The fix for this one is to rename "Intl" to "International". The name is important because other text identifies the requirements for the name International but not for Intl.

Proposed resolution:

Change 17.5.2.1 [type.descriptions], paragraph 1, from:

> The Requirements subclauses may describe names that are used to specify constraints on template arguments.153) These names are used in clauses 20, 23, 25, and 26 to describe the types that may be supplied as arguments by a C++ program when instantiating template components from the library.

to:

> The Requirements subclauses may describe names that are used to specify constraints on template arguments.153) These names are used in library clauses to describe the types that may be supplied as arguments by a C++ program when instantiating template components from the library.

In the front matter of class 22, locales, add:

> Template parameter types internT and externT shall meet the requirements of charT (described in 21 [strings]).

Rationale:

Again, a blanket clause isn't blanket enough. Also, we've got a couple of names that we don't have blanket requirement statements for. The only issue is what to do about stateT. This wording is thin, but probably adequate.

### 496. Illegal use of "T" in vector<bool>

Section: 23.3.6 [vector] Status: CD1 Submitter: richard@ex-parrot.com Opened: 2005-02-10 Last modified: 2008-09-26

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Discussion:

In the synopsis of the std::vector<bool> specialisation in 23.3.6 [vector], the non-template assign() function has the signature

      void assign( size_type n, const T& t );

The type, T, is not defined in this context.

Proposed resolution:

Replace "T" with "value_type".

### 497. meaning of numeric_limits::traps for floating point types

Section: 18.3.1.2 [numeric.limits.members] Status: CD1 Submitter: Martin Sebor Opened: 2005-03-02 Last modified: 2008-09-26

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Discussion:

18.2.1.2, p59 says this much about the traps member of numeric_limits:

> static const bool traps;
> -59- true if trapping is implemented for the type.204)
> Footnote 204: Required by LIA-1.

It's not clear what is meant by "is implemented" here.

In the context of floating point numbers it seems reasonable to expect to be able to use traps to determine whether a program can "safely" use infinity(), quiet_NaN(), etc., in arithmetic expressions, that is without causing a trap (i.e., on UNIX without having to worry about getting a signal). When traps is true, I would expect any of the operations in section 7 of IEEE 754 to cause a trap (and my program to get a SIGFPE). So, for example, on Alpha, I would expect traps to be true by default (unless I compiled my program with the -ieee option), false by default on most other popular architectures, including IA64, MIPS, PA-RISC, PPC, SPARC, and x86 which require traps to be explicitly enabled by the program.

Another possible interpretation of p59 is that traps should be true on any implementation that supports traps regardless of whether they are enabled by default or not. I don't think such an interpretation makes the traps member very useful, even though that is how traps is implemented on several platforms. It is also the only way to implement traps on platforms that allow programs to enable and disable trapping at runtime.

Proposed resolution:

Change p59 to read:

> True if, at program startup, there exists a value of the type that would cause an arithmetic operation using that value to trap.

Rationale:

Real issue, since trapping can be turned on and off. Unclear what a static query can say about a dynamic issue. The real advice we should give users is to use cfenv for these sorts of queries. But this new proposed resolution is at least consistent and slightly better than nothing.

### 498. Requirements for partition() and stable_partition() too strong

Section: 25.3.13 [alg.partitions] Status: WP Submitter: Sean Parent, Joe Gottman Opened: 2005-05-04 Last modified: 2009-10-26

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Discussion:

Problem: The iterator requirements for partition() and stable_partition() [25.2.12] are listed as BidirectionalIterator, however, there are efficient algorithms for these functions that only require ForwardIterator that have been known since before the standard existed. The SGI implementation includes these (see http://www.sgi.com/tech/stl/partition.html and http://www.sgi.com/tech/stl/stable_partition.html).

[ 2009-04-30 Alisdair adds: ]

> Now we have concepts this is easier to express!

> Proposed resolution:

> Add the following signature to:

> Header `<algorithm>` synopsis [algorithms.syn]
> p3 Partitions 25.3.13 [alg.partitions]

> >      template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred>
> >        requires ShuffleIterator<Iter>
> >              && CopyConstructible<Pred>
> >        Iter partition(Iter first, Iter last, Pred pred);

> Update p3 Partitions 25.3.13 [alg.partitions]:

> > Complexity: At most `(last - first)/2` swaps. Exactly `last - first` applications of the predicate are done. If `Iter` satisfies `BidirectionalIterator`, at most `(last - first)/2` swaps. Exactly `last - first` applications of the predicate are done.

> > If `Iter` merely satisfied `ForwardIterator` at most `(last - first)` swaps are done. Exactly `(last - first)` applications of the predicate are done.

> [Editorial note: I looked for existing precedent in how we might call out distinct overloads overloads from a set of constrained templates, but there is not much existing practice to lean on. advance/distance were the only algorithms I could find, and that wording is no clearer.]

[ 2009-07 Frankfurt ]

> Hinnant: if you want to partition your std::forward_list, you'll need partition() to accept ForwardIterators.

> No objection to Ready.

> Move to Ready.

Proposed resolution:

Change 25.2.12 from

>     template<class BidirectionalIterator, class Predicate>
>     BidirectionalIterator partition(BidirectionalIterato r first,
>                                     BidirectionalIterator last,
>                                     Predicate pred);

to

>     template<class ForwardIterator, class Predicate>
>     ForwardIterator partition(ForwardIterator first,
>                               ForwardIterator last,
>                               Predicate pred);

Change the complexity from

> At most (last - first)/2 swaps are done. Exactly (last - first) applications of the predicate are done.

to

> If ForwardIterator is a bidirectional_iterator, at most (last - first)/2 swaps are done; otherwise at most (last - first) swaps are done. Exactly (last - first) applications of the predicate are done.

Rationale:

Partition is a "foundation" algorithm useful in many contexts (like sorting as just one example) - my motivation for extending it to include forward iterators is foward_list - without this extension you can't partition an foward_list (without writing your own partition). Holes like this in the standard library weaken the argument for generic programming (ideally I'd be able to provide a library that would refine std::partition() to other concepts without fear of conflicting with other libraries doing the same - but that is a digression). I consider the fact that partition isn't defined to work for ForwardIterator a minor embarrassment.

[Mont Tremblant: Moved to Open, request motivation and use cases by next meeting. Sean provided further rationale by post-meeting mailing.]

### 505. Result_type in random distribution requirements

Section: X [rand.req], TR1 5.1.1 [tr.rand.req] Status: CD1 Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

Table 17: Random distribution requirements

Row 1 requires that each random distribution provide a nested type "input_type"; this type denotes the type of the values that the distribution consumes.

Inspection of all distributions in [tr.rand.dist] reveals that each distribution provides a second typedef ("result_type") that denotes the type of the values the distribution produces when called.

Proposed resolution:

It seems to me that this is also a requirement for all distributions and should therefore be indicated as such via a new second row to this table 17:

X::result_type | T | --- | compile-time

[ Berlin: Voted to WP. N1932 adopts the proposed resolution: see Table 5 row 1. ]

### 507. Missing requirement for variate_generator::operator()

Section: 26.5 [rand], TR1 5.1.3 [tr.rand.var] Status: CD1 Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

Paragraph 11 of [tr.rand.var] equires that the member template

>     template<class T> result_type operator() (T value);

return

>     distribution()(e, value)

However, not all distributions have an operator() with a corresponding signature.

[ Berlin: As a working group we voted in favor of N1932 which makes this moot: variate_generator has been eliminated. Then in full committee we voted to give this issue WP status (mistakenly). ]

Proposed resolution:

We therefore recommend that we insert the following precondition before paragraph 11:

> Precondition: `distribution().operator()(e,value)` is well-formed.

### 508. Bad parameters for ranlux64_base_01

Section: 26.5.5 [rand.predef], TR1 5.1.5 [tr.rand.predef] Status: CD1 Submitter: Walter Brown Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

The fifth of these engines with predefined parameters, ranlux64_base_01, appears to have an unintentional error for which there is a simple correction. The two pre-defined subtract_with_carry_01 engines are given as:

>     typedef subtract_with_carry_01<float,  24, 10, 24> ranlux_base_01;
>     typedef subtract_with_carry_01<double, 48, 10, 24> ranlux64_base_01;

We demonstrate below that ranlux64_base_01 fails to meet the intent of the random number generation proposal, but that the simple correction to

>     typedef subtract_with_carry_01<double, 48,  5, 12> ranlux64_base_01;

does meet the intent of defining well-known good parameterizations.

The ranlux64_base_01 engine as presented fails to meet the intent for predefined engines, stated in proposal N1398 (section E):

> In order to make good random numbers available to a large number of library users, this proposal not only defines generic random-number engines, but also provides a number of predefined well-known good parameterizations for those.

The predefined ranlux_base_01 engine has been proven [1,2,3] to have a very long period and so meets this criterion. This property makes it suitable for use in the excellent discard_block engines defined subsequently. The proof of long period relies on the fact (proven in [1]) that 2**(w*r) - 2**(w*s) + 1 is prime (w, r, and s are template parameters to subtract_with_carry_01, as defined in [tr.rand.eng.sub1]).

The ranlux64_base_01 engine as presented in [tr.rand.predef] uses w=48, r=24, s=10. For these numbers, the combination 2**(w*r)-2**(w*s)+1 is non-prime (though explicit factorization would be a challenge). In consequence, while it is certainly possible for some seeding states that this engine would have a very long period, it is not at all "well-known" that this is the case. The intent in the N1398 proposal involved the base of the ranlux64 engine, which finds heavy use in the physics community. This is isomorphic to the predefined ranlux_base_01, but exploits the ability of double variables to hold (at least) 48 bits of mantissa, to deliver 48 random bits at a time rather than 24.

Proposed resolution:

To achieve this intended behavior, the correct template parameteriztion would be:

>     typedef subtract_with_carry_01<double, 48, 5, 12> ranlux64_base_01;

The sequence of mantissa bits delivered by this is isomorphic (treating each double as having the bits of two floats) to that delivered by ranlux_base_01.

References:

1. F. James, Comput. Phys. Commun. 60(1990) 329
2. G. Marsaglia and A. Zaman, Ann. Appl. Prob 1(1991) 462
3. M. Luscher, Comput. Phys. Commun. 79(1994) 100-110

[ Berlin: Voted to WP. N1932 adopts the proposed resolution in 26.3.5, just above paragraph 5. ]

### 518. Are insert and erase stable for unordered_multiset and unordered_multimap?

Section: 23.2.5 [unord.req], TR1 6.3.1 [tr.unord.req] Status: CD1 Submitter: Matt Austern Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

Issue 371 deals with stability of multiset/multimap under insert and erase (i.e. do they preserve the relative order in ranges of equal elements). The same issue applies to unordered_multiset and unordered_multimap.

[ Moved to open (from review): There is no resolution. ]

[ Toronto: We have a resolution now. Moved to Review. Some concern was noted as to whether this conflicted with existing practice or not. An additional concern was in specifying (partial) ordering for an unordered container. ]

Proposed resolution:

Wording for the proposed resolution is taken from the equivalent text for associative containers.

Change 23.2.5 [unord.req], Unordered associative containers, paragraph 6 to:

> An unordered associative container supports unique keys if it may contain at most one element for each key. Otherwise, it supports equivalent keys. `unordered_set` and `unordered_map` support unique keys. `unordered_multiset` and `unordered_multimap` support equivalent keys. In containers that support equivalent keys, elements with equivalent keys are adjacent to each other. For `unordered_multiset` and `unordered_multimap`,`insert` and `erase` preserve the relative ordering of equivalent elements.

Change 23.2.5 [unord.req], Unordered associative containers, paragraph 8 to:

> The elements of an unordered associative container are organized into buckets. Keys with the same hash code appear in the same bucket. The number of buckets is automatically increased as elements are added to an unordered associative container, so that the average number of elements per bucket is kept below a bound. Rehashing invalidates iterators, changes ordering between elements, and changes which buckets elements appear in, but does not invalidate pointers or references to elements. For `unordered_multiset` and `unordered_multimap`, rehashing preserves the relative ordering of equivalent elements.

### 519. Data() undocumented

Section: 23.3.1 [array], TR1 6.2.2 [tr.array.array] Status: CD1 Submitter: Pete Becker Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

`array<>::data()` is present in the class synopsis, but not documented.

Proposed resolution:

Add a new section, after 6.2.2.3:

>     T*       data()
>     const T* data() const;

Returns: `elems`.

Change 6.2.2.4/2 to:

> In the case where `N == 0`, `begin() == end()`. The return value of `data()` is unspecified.

### 520. Result_of and pointers to data members

Section: 20.7.11.1 [func.bind], TR1 3.6 [tr.func.bind] Status: CD1 Submitter: Pete Becker Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

In the original proposal for binders, the return type of bind() when called with a pointer to member data as it's callable object was defined to be mem_fn(ptr); when Peter Dimov and I unified the descriptions of the TR1 function objects we hoisted the descriptions of return types into the INVOKE pseudo-function and into result_of. Unfortunately, we left pointer to member data out of result_of, so bind doesn't have any specified behavior when called with a pointer to member data.

Proposed resolution:

[ Pete and Peter will provide wording. ]

In 20.5.4 [lib.func.ret] ([tr.func.ret]) p3 add the following bullet after bullet 2:

3. If `F` is a member data pointer type `R T::*`, `type` shall be `cv R&` when `T1` is `cv U1&`, `R` otherwise.

[ Peter provided wording. ]

### 521. Garbled requirements for argument_type in reference_wrapper

Section: 20.7.5 [refwrap], TR1 2.1.2 [tr.util.refwrp.refwrp] Status: CD1 Submitter: Pete Becker Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

2.1.2/3, second bullet item currently says that reference_wrapper<T> is derived from unary_function<T, R> if T is:

> a pointer to member function type with cv-qualifier cv and no arguments; the type T1 is cv T* and R is the return type of the pointer to member function;

The type of T1 can't be cv T*, 'cause that's a pointer to a pointer to member function. It should be a pointer to the class that T is a pointer to member of. Like this:

> a pointer to a member function R T0::f() cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*

Similarly, bullet item 2 in 2.1.2/4 should be:

> a pointer to a member function R T0::f(T2) cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*

Proposed resolution:

Change bullet item 2 in 2.1.2/3:

> - a pointer to member function type with cv-qualifier `cv` and no arguments; the type `T1` is `cv T*` and `R` is the return type of the pointer to member function `R T0::f() cv` (where `cv` represents the member function's cv-qualifiers); the type `T1` is `cv T0*`

Change bullet item 2 in 2.1.2/4:

> - a pointer to member function with cv-qualifier `cv` and taking one argument of type `T2`; the type `T1` is `cv T*` and `R` is the return type of the pointer to member function `R T0::f(T2) cv` (where `cv` represents the member function's cv-qualifiers); the type `T1` is `cv T0*`

### 522. Tuple doesn't define swap

Section: 20.5 [tuple], TR1 6.1 [tr.tuple] Status: CD1 Submitter: Andy Koenig Opened: 2005-07-03 Last modified: 2008-09-26

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Discussion:

Tuple doesn't define swap(). It should.

[ Berlin: Doug to provide wording. ]

[ Batavia: Howard to provide wording. ]

[ Toronto: Howard to provide wording (really this time). ]

[ Bellevue: Alisdair provided wording. ]

Proposed resolution:

Add these signatures to 20.5 [tuple]

>     template <class... Types>
>       void swap(tuple<Types...>& x, tuple<Types...>& y);
>     template <class... Types>
>       void swap(tuple<Types...>&& x, tuple<Types...>& y);
>     template <class... Types>
>       void swap(tuple<Types...>& x, tuple<Types...>&& y);

Add this signature to 20.5.2 [tuple.tuple]

>     void swap(tuple&&);

Add the following two sections to the end of the tuple clauses

> 20.3.1.7 tuple swap [tuple.swap]

>     void swap(tuple&& rhs);

> > Requires: Each type in `Types` shall be `Swappable`.

> > Effects: Calls `swap` for each element in `*this` and its corresponding element in `rhs`.

> > Throws: Nothing, unless one of the element-wise `swap` calls throw an exception.

> 20.3.1.8 tuple specialized algorithms [tuple.special]

>     template <class... Types>
>       void swap(tuple<Types...>& x, tuple<Types...>& y);
>     template <class... Types>
>       void swap(tuple<Types...>&& x, tuple<Types...>& y);
>     template <class... Types>
>       void swap(tuple<Types...>& x, tuple<Types...>&& y);

> > Effects: x.swap(y)

### 524. regex named character classes and case-insensitivity don't mix

Section: 28 [re] Status: CD1 Submitter: Eric Niebler Opened: 2005-07-01 Last modified: 2008-09-26

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Discussion:

This defect is also being discussed on the Boost developers list. The full discussion can be found here: http://lists.boost.org/boost/2005/07/29546.php

-- Begin original message --

Also, I may have found another issue, closely related to the one under discussion. It regards case-insensitive matching of named character classes. The regex_traits<> provides two functions for working with named char classes: lookup_classname and isctype. To match a char class such as [[:alpha:]], you pass "alpha" to lookup_classname and get a bitmask. Later, you pass a char and the bitmask to isctype and get a bool yes/no answer.

But how does case-insensitivity work in this scenario? Suppose we're doing a case-insensitive match on [[:lower:]]. It should behave as if it were [[:lower:][:upper:]], right? But there doesn't seem to be enough smarts in the regex_traits interface to do this.

Imagine I write a traits class which recognizes [[:fubar:]], and the "fubar" char class happens to be case-sensitive. How is the regex engine to know that? And how should it do a case-insensitive match of a character against the [[:fubar:]] char class? John, can you confirm this is a legitimate problem?

I see two options:

1) Add a bool icase parameter to lookup_classname. Then, lookup_classname( "upper", true ) will know to return lower|upper instead of just upper.

2) Add a isctype_nocase function

I prefer (1) because the extra computation happens at the time the pattern is compiled rather than when it is executed.

-- End original message --

For what it's worth, John has also expressed his preference for option (1) above.

Proposed resolution:

Adopt the proposed resolution in N2409.

[ Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 527. tr1::bind has lost its Throws clause

Section: 20.7.11.1.3 [func.bind.bind], TR1 3.6.3 [tr.func.bind.bind] Status: CD1 Submitter: Peter Dimov Opened: 2005-10-01 Last modified: 2008-09-26

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Discussion:

The original bind proposal gives the guarantee that tr1::bind(f, t1, ..., tN) does not throw when the copy constructors of f, t1, ..., tN don't.

This guarantee is not present in the final version of TR1.

I'm pretty certain that we never removed it on purpose. Editorial omission? :-)

[ Berlin: not quite editorial, needs proposed wording. ]

[ Batavia: Doug to translate wording to variadic templates. ]

[ Toronto: We agree but aren't quite happy with the wording. The "t"'s no longer refer to anything. Alan to provide improved wording. ]

[ Pre-Bellevue: Alisdair provided wording. ]

TR1 proposed resolution:

> In TR1 3.6.3 [tr.func.bind.bind], add a new paragraph after p2:

> > Throws: Nothing unless one of the copy constructors of `f, t1, t2, ..., tN` throws an exception.

> Add a new paragraph after p4:

> > Throws: nothing unless one of the copy constructors of `f, t1, t2, ..., tN` throws an exception.

Proposed resolution:

In 20.7.11.1.3 [func.bind.bind], add a new paragraph after p2:

> Throws: Nothing unless the copy constructor of `F` or of one of the types in the `BoundArgs...` pack expansion throws an exception.

In 20.7.11.1.3 [func.bind.bind], add a new paragraph after p4:

> Throws: Nothing unless the copy constructor of `F` or of one of the types in the `BoundArgs...` pack expansion throws an exception.

### 530. Must elements of a string be contiguous?

Section: 21.4 [basic.string] Status: CD1 Submitter: Matt Austern Opened: 2005-11-15 Last modified: 2008-09-26

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Discussion:

Issue 69, which was incorporated into C++03, mandated that the elements of a vector must be stored in contiguous memory. Should the same also apply to `basic_string`?

We almost require contiguity already. Clause 23.4.4 [multiset] defines `operator[]` as `data()[pos]`. What's missing is a similar guarantee if we access the string's elements via the iterator interface.

Given the existence of `data()`, and the definition of `operator[]` and `at` in terms of `data`, I don't believe it's possible to write a useful and standard- conforming `basic_string` that isn't contiguous. I'm not aware of any non-contiguous implementation. We should just require it.

Proposed resolution:

Add the following text to the end of 21.4 [basic.string], paragraph 2.

> The characters in a string are stored contiguously, meaning that if `s` is a `basic_string<charT, Allocator>`, then it obeys the identity `&*(s.begin() + n) == &*s.begin() + n` for all `0 <= n < s.size()`.

Rationale:

Not standardizing this existing practice does not give implementors more freedom. We thought it might a decade ago. But the vendors have spoken both with their implementations, and with their voice at the LWG meetings. The implementations are going to be contiguous no matter what the standard says. So the standard might as well give string clients more design choices.

### 531. array forms of unformatted input functions

Section: 27.7.1.3 [istream.unformatted] Status: CD1 Submitter: Martin Sebor Opened: 2005-11-23 Last modified: 2008-09-26

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Discussion:

The array forms of unformatted input functions don't seem to have well-defined semantics for zero-element arrays in a couple of cases. The affected ones (`istream::get()` and `istream::getline()`) are supposed to terminate when `(n - 1)` characters are stored, which obviously can never be true when `(n == 0)` holds to start with. See c++std-lib-16071.

Proposed resolution:

I suggest changing 27.6.1.3, p7 (`istream::get()`), bullet 1 to read:

- `(n < 1)` is true or `(n - 1)` characters are stored;

Change 27.6.1.3, p9:

> If the function stores no characters, it calls `setstate(failbit)` (which may throw `ios_base::failure` (27.4.4.3)). In any case, if `(n > 0)` is true it then stores a null character into the next successive location of the array.

and similarly p17 (`istream::getline()`), bullet 3 to:

- `(n < 1)` is true or `(n - 1)` characters are stored (in which case the function calls `setstate(failbit)`).

In addition, to clarify that `istream::getline()` must not store the terminating NUL character unless the the array has non-zero size, Robert Klarer suggests in c++std-lib-16082 to change 27.6.1.3, p20 to read:

> In any case, provided `(n > 0)` is true, it then stores a null character (using charT()) into the next successive location of the array.

[ post-Redmond: Pete noticed that the current resolution for `get` requires writing to out of bounds memory when `n == 0`. Martin provided fix. ]

### 533. typo in 2.2.3.10/1

Section: 20.8.15.2.11 [util.smartptr.getdeleter], TR1 2.2.3.10 [tr.util.smartptr.getdeleter] Status: CD1 Submitter: Paolo Carlini Opened: 2005-11-09 Last modified: 2009-05-01

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Discussion:

I'm seeing something that looks like a typo. The Return of `get_deleter` says:

> If `*this` owns a deleter `d`...

but `get_deleter` is a free function!

Proposed resolution:

Therefore, I think should be:

> If `*this p` owns a deleter `d`...

### 534. Missing basic_string members

Section: 21.4 [basic.string] Status: CD1 Submitter: Alisdair Meredith Opened: 2005-11-16 Last modified: 2008-09-26

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Discussion:

OK, we all know std::basic_string is bloated and already has way too many members. However, I propose it is missing 3 useful members that are often expected by users believing it is a close approximation of the container concept. All 3 are listed in table 71 as 'optional'

i/ pop_back.

This is the one I feel most strongly about, as I only just discovered it was missing as we are switching to a more conforming standard library <g>

I find it particularly inconsistent to support push_back, but not pop_back.

ii/ back.

There are certainly cases where I want to examine the last character of a string before deciding to append, or to trim trailing path separators from directory names etc. *rbegin() somehow feels inelegant.

iii/ front

This one I don't feel strongly about, but if I can get the first two, this one feels that it should be added as a 'me too' for consistency.

I believe this would be similarly useful to the data() member recently added to vector, or at() member added to the maps.

Proposed resolution:

Add the following members to definition of class template basic_string, 21.3p7

>     void pop_back ()

>     const charT & front() const
>     charT & front()

>     const charT & back() const
>     charT & back()

Add the following paragraphs to basic_string description

21.3.4p5

>     const charT & front() const
>     charT & front()

> Precondition: `!empty()`

> Effects: Equivalent to `operator[](0)`.

21.3.4p6

>     const charT & back() const
>     charT & back()

> Precondition: `!empty()`

> Effects: Equivalent to `operator[]( size() - 1)`.

21.3.5.5p10

>     void pop_back ()

> Precondition: `!empty()`

> Effects: Equivalent to `erase( size() - 1, 1 )`.

Update Table 71: (optional sequence operations) Add basic_string to the list of containers for the following operations.

>     a.front()
>     a.back()
>     a.push_back()
>     a.pop_back()
>     a[n]

[ Berlin: Has support. Alisdair provided wording. ]

### 535. std::string::swap specification poorly worded

Section: 21.4.6.8 [string::swap] Status: CD1 Submitter: Beman Dawes Opened: 2005-12-14 Last modified: 2008-09-26

View all other issues in [string::swap].

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Discussion:

std::string::swap currently says for effects and postcondition:

> Effects: Swaps the contents of the two strings.

> Postcondition: `*this` contains the characters that were in `s`, `s` contains the characters that were in `*this`.

Specifying both Effects and Postcondition seems redundant, and the postcondition needs to be made stronger. Users would be unhappy if the characters were not in the same order after the swap.

Proposed resolution:

> Effects: Swaps the contents of the two strings.

> Postcondition: `*this` contains the same sequence of characters that were was in `s`, `s` contains the same sequence of characters that were was in `*this`.

### 537. Typos in the signatures in 27.6.1.3/42-43 and 27.6.2.4

Section: 27.7.1.3 [istream.unformatted] Status: CD1 Submitter: Paolo Carlini Opened: 2006-02-12 Last modified: 2008-09-26

View all other issues in [istream.unformatted].

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Discussion:

In the most recent working draft, I'm still seeing:

>     seekg(off_type& off, ios_base::seekdir dir)

and

>     seekp(pos_type& pos)

>     seekp(off_type& off, ios_base::seekdir dir)

that is, by reference off and pos arguments.

Proposed resolution:

After 27.6.1.3p42 change:

>     basic_istream<charT,traits>& seekg(off_type& off, ios_base::seekdir dir);

After 27.6.2.4p1 change:

>     basic_ostream<charT,traits>& seekp(pos_type& pos);

After 27.6.2.4p3 change:

>     basic_ostream<charT,traits>& seekp(off_type& off, ios_base::seekdir dir);

### 538. 241 again: Does unique_copy() require CopyConstructible and Assignable?

Section: 25.3.9 [alg.unique] Status: CD1 Submitter: Howard Hinnant Opened: 2006-02-09 Last modified: 2008-09-26

View all other issues in [alg.unique].

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Discussion:

I believe I botched the resolution of 241 "Does unique_copy() require CopyConstructible and Assignable?" which now has WP status.

This talks about `unique_copy` requirements and currently reads:

> -5- Requires: The ranges `[first, last)` and `[result, result+(last-first))` shall not overlap. The expression `*result = *first` shall be valid. If neither `InputIterator` nor `OutputIterator` meets the requirements of forward iterator then the value type of `InputIterator` must be CopyConstructible (20.1.3). Otherwise CopyConstructible is not required.

The problem (which Paolo discovered) is that when the iterators are at their most restrictive (`InputIterator`, `OutputIterator`), then we want `InputIterator::value_type` to be both `CopyConstructible` and `CopyAssignable` (for the most efficient implementation). However this proposed resolution only makes it clear that it is `CopyConstructible`, and that one can assign from `*first` to `*result`. This latter requirement does not necessarily imply that you can:

>     *first = *first;

Proposed resolution:

> -5- Requires: The ranges `[first, last)` and `[result, result+(last-first))` shall not overlap. The expression `*result = *first` shall be valid. If neither `InputIterator` nor `OutputIterator` meets the requirements of forward iterator then the value type `value_type` of `InputIterator` must be CopyConstructible (20.1.3) and Assignable. Otherwise CopyConstructible is not required.

### 540. shared_ptr<void>::operator*()

Section: 20.8.15.2.5 [util.smartptr.shared.obs], TR1 2.2.3.5 [tr.util.smartptr.shared.obs] Status: CD1 Submitter: Martin Sebor Opened: 2005-10-15 Last modified: 2008-09-26

View all other issues in [util.smartptr.shared.obs].

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Discussion:

I'm trying to reconcile the note in tr.util.smartptr.shared.obs, p6 that talks about the operator*() member function of shared_ptr:

> Notes: When T is void, attempting to instantiate this member function renders the program ill-formed. [Note: Instantiating shared_ptr<void> does not necessarily result in instantiating this member function. --end note]

with the requirement in temp.inst, p1:

> The implicit instantiation of a class template specialization causes the implicit instantiation of the declarations, but not of the definitions...

I assume that what the note is really trying to say is that "instantiating shared_ptr<void> *must not* result in instantiating this member function." That is, that this function must not be declared a member of shared_ptr<void>. Is my interpretation correct?

Proposed resolution:

Change 2.2.3.5p6

> -6- Notes: When `T` is `void`, attempting to instantiate this member function renders the program ill-formed. [Note: Instantiating `shared_ptr<void>` does not necessarily result in instantiating this member function. --end note] it is unspecified whether this member function is declared or not, and if so, what its return type is, except that the declaration (although not necessarily the definition) of the function shall be well-formed.

### 541. shared_ptr template assignment and void

Section: 20.8.15.2 [util.smartptr.shared], TR1 2.2.3 [tr.util.smartptr.shared] Status: CD1 Submitter: Martin Sebor Opened: 2005-10-16 Last modified: 2008-09-26

View all other issues in [util.smartptr.shared].

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Discussion:

Is the void specialization of the template assignment operator taking a shared_ptr<void> as an argument supposed be well-formed?

I.e., is this snippet well-formed:

>     shared_ptr<void> p;
>     p.operator=<void>(p);

Gcc complains about auto_ptr<void>::operator*() returning a reference to void. I suspect it's because shared_ptr has two template assignment operators, one of which takes auto_ptr, and the auto_ptr template gets implicitly instantiated in the process of overload resolution.

The only way I see around it is to do the same trick with auto_ptr<void> operator*() as with the same operator in shared_ptr<void>.

PS Strangely enough, the EDG front end doesn't mind the code, even though in a small test case (below) I can reproduce the error with it as well.

>     template <class T>
>     struct A { T& operator*() { return *(T*)0; } };

>     template <class T>
>     struct B {
>         void operator= (const B&) { }
>         template <class U>
>         void operator= (const B<U>&) { }
>         template <class U>
>         void operator= (const A<U>&) { }
>     };

>     int main ()
>     {
>         B<void> b;
>         b.operator=<void>(b);
>     }

Proposed resolution:

In [lib.memory] change:

>     template<class X> class auto_ptr;
>     template<> class auto_ptr<void>;

In [lib.auto.ptr]/2 add the following before the last closing brace:

>     template<> class auto_ptr<void>
>     {
>     public:
>         typedef void element_type;
>     };

### 542. shared_ptr observers

Section: 20.8.15.2.5 [util.smartptr.shared.obs], TR1 2.2.3.5 [tr.util.smartptr.shared.obs] Status: CD1 Submitter: Martin Sebor Opened: 2005-10-18 Last modified: 2008-09-26

View all other issues in [util.smartptr.shared.obs].

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Discussion:

Peter Dimov wrote: To: C++ libraries mailing list Message c++std-lib-15614 [...] The intent is for both use_count() and unique() to work in a threaded environment. They are intrinsically prone to race conditions, but they never return garbage.

This is a crucial piece of information that I really wish were captured in the text. Having this in a non-normative note would have made everything crystal clear to me and probably stopped me from ever starting this discussion :) Instead, the sentence in p12 "use only for debugging and testing purposes, not for production code" very strongly suggests that implementations can and even are encouraged to return garbage (when threads are involved) for performance reasons.

How about adding an informative note along these lines:

> Note: Implementations are encouraged to provide well-defined behavior for use_count() and unique() even in the presence of multiple threads.

I don't necessarily insist on the exact wording, just that we capture the intent.

Proposed resolution:

Change 20.8.15.2.5 [util.smartptr.shared.obs] p12:

> [Note: `use_count()` is not necessarily efficient. Use only for debugging and testing purposes, not for production code. --end note]

Change 20.8.15.3.5 [util.smartptr.weak.obs] p3:

> [Note: `use_count()` is not necessarily efficient. Use only for debugging and testing purposes, not for production code. --end note]

### 543. valarray slice default constructor

Section: 26.6.4 [class.slice] Status: CD1 Submitter: Howard Hinnant Opened: 2005-11-03 Last modified: 2008-09-26

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Discussion:

If one explicitly constructs a slice or glice with the default constructor, does the standard require this slice to have any usable state? It says "creates a slice which specifies no elements", which could be interpreted two ways:

1. There are no elements to which the slice refers (i.e. undefined).
2. The slice specifies an array with no elements in it (i.e. defined).

Here is a bit of code to illustrate:

>     #include <iostream>
>     #include <valarray>

>     int main()
>     {
>         std::valarray<int> v(10);
>         std::valarray<int> v2 = v[std::slice()];
>         std::cout << "v[slice()].size() = " << v2.size() << '\n';
>     }

Is the behavior undefined? Or should the output be:

>     v[slice()].size() = 0

There is a similar question and wording for gslice at 26.3.6.1p1.

Proposed resolution:

[Martin suggests removing the second sentence in 26.6.4.1 [cons.slice] as well.]

Change 26.6.4.1 [cons.slice]:

> 1 - The default constructor for `slice` creates a `slice` which specifies no elements. The default constructor is equivalent to `slice(0, 0, 0)`. A default constructor is provided only to permit the declaration of arrays of slices. The constructor with arguments for a slice takes a start, length, and stride parameter.

Change 26.6.6.1 [gslice.cons]:

> 1 - The default constructor creates a `gslice` which specifies no elements. The default constructor is equivalent to `gslice(0, valarray<size_t>(), valarray<size_t>())`. The constructor with arguments builds a `gslice` based on a specification of start, lengths, and strides, as explained in the previous section.

### 545. When is a deleter deleted?

Section: 20.8.15.2.11 [util.smartptr.getdeleter], TR1 2.2.3.2 [tr.util.smartptr.shared.dest] Status: CD1 Submitter: Matt Austern Opened: 2006-01-10 Last modified: 2008-09-26

View all other issues in [util.smartptr.getdeleter].

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Discussion:

The description of ~shared_ptr doesn't say when the shared_ptr's deleter, if any, is destroyed. In principle there are two possibilities: it is destroyed unconditionally whenever ~shared_ptr is executed (which, from an implementation standpoint, means that the deleter is copied whenever the shared_ptr is copied), or it is destroyed immediately after the owned pointer is destroyed (which, from an implementation standpoint, means that the deleter object is shared between instances). We should say which it is.

Proposed resolution:

Add after the first sentence of 20.8.15.2.11 [util.smartptr.getdeleter]/1:

> The returned pointer remains valid as long as there exists a `shared_ptr` instance that owns `d`.

> [Note: it is unspecified whether the pointer remains valid longer than that. This can happen if the implementation doesn't destroy the deleter until all `weak_ptr` instances in the ownership group are destroyed. -- end note]

### 550. What should the return type of pow(float,int) be?

Section: 26.8 [c.math] Status: CD1 Submitter: Howard Hinnant Opened: 2006-01-12 Last modified: 2008-09-26

View all other issues in [c.math].

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Discussion:

Assuming we adopt the C compatibility package from C99 what should be the return type of the following signature be:

>     ?  pow(float, int);

C++03 says that the return type should be `float`. TR1 and C90/99 say the return type should be `double`. This can put clients into a situation where C++03 provides answers that are not as high quality as C90/C99/TR1. For example:

>     #include <math.h>

>     int main()
>     {
>         float x = 2080703.375F;
>         double y = pow(x, 2);
>     }

Assuming an IEEE 32 bit float and IEEE 64 bit double, C90/C99/TR1 all suggest:

>     y = 4329326534736.390625

which is exactly right. While C++98/C++03 demands:

>     y = 4329326510080.

which is only approximately right.

I recommend that C++0X adopt the mixed mode arithmetic already adopted by Fortran, C and TR1 and make the return type of `pow(float,int)` be `double`.

[ Kona (2007): Other functions that are affected by this issue include `ldexp`, `scalbln`, and `scalbn`. We also believe that there is a typo in 26.7/10: `float nexttoward(float, long double);` [sic] should be `float nexttoward(float, float);` Proposed Disposition: Review (the proposed resolution appears above, rather than below, the heading "Proposed resolution") ]

[

Howard, post Kona:

> Unfortunately I strongly disagree with a part of the resolution from Kona. I am moving from New to Open instead of to Review because I do not believe we have consensus on the intent of the resolution.

> This issue does not include `ldexp`, `scalbln`, and `scalbn` because the second integral parameter in each of these signatures (from C99) is not a generic parameter according to C99 7.22p2. The corresponding C++ overloads are intended (as far as I know) to correspond directly to C99's definition of generic parameter.

> For similar reasons, I do not believe that the second `long double` parameter of `nexttoward`, nor the return type of this function, is in error. I believe the correct signature is:

> >     float nexttoward(float, long double);

> which is what both the C++0X working paper and C99 state (as far as I currently understand).

> This is really only about `pow(float, int)`. And this is because C++98 took one route (with `pow` only) and C99 took another (with many math functions in `<tgmath.h>`. The proposed resolution basically says: C++98 got it wrong and C99 got it right; let's go with C99.

]

[ Bellevue: ]

> This signature was not picked up from C99. Instead, if one types pow(2.0f,2), the promotion rules will invoke "double pow(double, double)", which generally gives special treatment for integral exponents, preserving full accuracy of the result. New proposed wording provided.

Proposed resolution:

Change 26.8 [c.math] p10:

> The added signatures are:

> >     ...
> >     float pow(float, int);
> >     ...
> >     double pow(double, int);
> >     ...
> >     long double pow(long double, int);

### 551. <ccomplex>

Section: 26.4.11 [cmplxh], TR1 8.3 [tr.c99.cmplxh] Status: CD1 Submitter: Howard Hinnant Opened: 2006-01-23 Last modified: 2008-09-26

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Discussion:

Previously xxx.h was parsable by C++. But in the case of C99's <complex.h> it isn't. Otherwise we could model it just like <string.h>, <cstring>, <string>:

- <string> : C++ API in namespace std
- <cstring> : C API in namespace std
- <string.h> : C API in global namespace

In the case of C's complex, the C API won't compile in C++. So we have:

- <complex> : C++ API in namespace std
- <ccomplex> : ?
- <complex.h> : ?

The ? can't refer to the C API. TR1 currently says:

- <complex> : C++ API in namespace std
- <ccomplex> : C++ API in namespace std
- <complex.h> : C++ API in global namespace

Proposed resolution:

Change 26.3.11 [cmplxh]:

> The header behaves as if it includes the header `<ccomplex>`., and provides sufficient using declarations to declare in the global namespace all function and type names declared or defined in the neader `<complex>`. [Note: `<complex.h>` does not promote any interface into the global namespace as there is no C interface to promote. --end note]

### 552. random_shuffle and its generator

Section: 25.3.12 [alg.random.shuffle] Status: CD1 Submitter: Martin Sebor Opened: 2006-01-25 Last modified: 2008-09-26

View all other issues in [alg.random.shuffle].

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Discussion:

...is specified to shuffle its range by calling swap but not how (or even that) it's supposed to use the RandomNumberGenerator argument passed to it.

Shouldn't we require that the generator object actually be used by the algorithm to obtain a series of random numbers and specify how many times its operator() should be invoked by the algorithm?

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 559. numeric_limits<const T>

Section: 18.3.1 [limits] Status: CD1 Submitter: Martin Sebor Opened: 2006-02-19 Last modified: 2008-09-26

View all other issues in [limits].

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Discussion:

18.3.1 [limits], p2 requires implementations to provide specializations of the `numeric_limits` template for each scalar type. While this could be interepreted to include cv-qualified forms of such types such an interepretation is not reflected in the synopsis of the `<limits>` header.

The absence of specializations of the template on cv-qualified forms of fundamental types makes `numeric_limits` difficult to use in generic code where the constness (or volatility) of a type is not always immediately apparent. In such contexts, the primary template ends up being instantiated instead of the provided specialization, typically yielding unexpected behavior.

Require that specializations of `numeric_limits` on cv-qualified fundamental types have the same semantics as those on the unqualifed forms of the same types.

Proposed resolution:

Add to the synopsis of the `<limits>` header, immediately below the declaration of the primary template, the following:

    template <class T> class numeric_limits<const T>;
    template <class T> class numeric_limits<volatile T>;
    template <class T> class numeric_limits<const volatile T>;

Add a new paragraph to the end of 18.3.1.1 [numeric.limits], with the following text:

-new-para- The value of each member of a `numeric_limits` specialization on a cv-qualified T is equal to the value of the same member of `numeric_limits<T>`.

[ Portland: Martin will clarify that user-defined types get cv-specializations automatically. ]

### 561. inserter overly generic

Section: 24.5.2.6.5 [inserter] Status: CD1 Submitter: Howard Hinnant Opened: 2006-02-21 Last modified: 2008-09-26

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Discussion:

The declaration of `std::inserter` is:

>     template <class Container, class Iterator>
>     insert_iterator<Container>
>     inserter(Container& x, Iterator i);

The template parameter `Iterator` in this function is completely unrelated to the template parameter `Container` when it doesn't need to be. This causes the code to be overly generic. That is, any type at all can be deduced as `Iterator`, whether or not it makes sense. Now the same is true of `Container`. However, for every free (unconstrained) template parameter one has in a signature, the opportunity for a mistaken binding grows geometrically.

It would be much better if `inserter` had the following signature instead:

>     template <class Container>
>     insert_iterator<Container>
>     inserter(Container& x, typename Container::iterator i);

Now there is only one free template parameter. And the second argument to `inserter` must be implicitly convertible to the container's iterator, else the call will not be a viable overload (allowing other functions in the overload set to take precedence). Furthermore, the first parameter must have a nested type named `iterator`, or again the binding to `std::inserter` is not viable. Contrast this with the current situation where any type can bind to `Container` or `Iterator` and those types need not be anything closely related to containers or iterators.

This can adversely impact well written code. Consider:

>     #include <iterator>
>     #include <string>

>     namespace my
>     {

>     template <class String>
>     struct my_type {};

>     struct my_container
>     {
>     template <class String>
>     void push_back(const my_type<String>&);
>     };

>     template <class String>
>     void inserter(const my_type<String>& m, my_container& c) {c.push_back(m);}

>     }  // my

>     int main()
>     {
>         my::my_container c;
>         my::my_type<std::string> m;
>         inserter(m, c);
>     }

Today this code fails because the call to `inserter` binds to `std::inserter` instead of to `my::inserter`. However with the proposed change `std::inserter` will no longer be a viable function which leaves only `my::inserter` in the overload resolution set. Everything works as the client intends.

To make matters a little more insidious, the above example works today if you simply change the first argument to an rvalue:

>         inserter(my::my_type(), c);

It will also work if instantiated with some string type other than `std::string` (or any other `std` type). It will also work if `<iterator>` happens to not get included.

And it will fail again for such inocuous reaons as `my_type` or `my_container` privately deriving from any `std` type.

It seems unfortunate that such simple changes in the client's code can result in such radically differing behavior.

Proposed resolution:

Change 24.2:

> 24.2 Header `<iterator>` synopsis

> >     ...
> >     template <class Container, class Iterator>
> >        insert_iterator<Container> inserter(Container& x, Iterator typename Container::iterator i);
> >     ...

Change 24.4.2.5:

> 24.4.2.5 Class template `insert_iterator`

> >     ...
> >     template <class Container, class Iterator>
> >        insert_iterator<Container> inserter(Container& x, Iterator typename Container::iterator i);
> >     ...

Change 24.4.2.6.5:

> 24.4.2.6.5 `inserter`

>     template <class Container, class Inserter>
>        insert_iterator<Container> inserter(Container& x, Inserter typename Container::iterator i);

> > -1- Returns: `insert_iterator<Container>(x,typename Container::iterator(i))`.

[ Kona (2007): This issue will probably be addressed as a part of the concepts overhaul of the library anyway, but the proposed resolution is correct in the absence of concepts. Proposed Disposition: Ready ]

### 562. stringbuf ctor inefficient

Section: 27.8 [string.streams] Status: CD1 Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2008-09-26

View all other issues in [string.streams].

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Discussion:

For better efficiency, the requirement on the stringbuf ctor that takes a string argument should be loosened up to let it set `epptr()` beyond just one past the last initialized character just like `overflow()` has been changed to be allowed to do (see issue 432). That way the first call to `sputc()` on an object won't necessarily cause a call to `overflow`. The corresponding change should be made to the string overload of the `str()` member function.

Proposed resolution:

Change 27.7.1.1, p3 of the Working Draft, N1804, as follows:

>     explicit basic_stringbuf(const basic_string<charT,traits,Allocator>& str,
>                    ios_base::openmode which = ios_base::in | ios_base::out);

> -3- Effects: Constructs an object of class `basic_stringbuf`, initializing the base class with `basic_streambuf()` (27.5.2.1), and initializing `mode` with `which`. Then calls `str(s)`. copies the content of str into the `basic_stringbuf` underlying character sequence. If `which & ios_base::out` is true, initializes the output sequence such that `pbase()` points to the first underlying character, `epptr()` points one past the last underlying character, and `pptr()` is equal to `epptr()` if `which & ios_base::ate` is true, otherwise `pptr()` is equal to `pbase()`. If `which & ios_base::in` is true, initializes the input sequence such that `eback()` and `gptr()` point to the first underlying character and `egptr()` points one past the last underlying character.

Change the Effects clause of the `str()` in 27.7.1.2, p2 to read:

> -2- Effects: Copies the contents of `s` into the `basic_stringbuf` underlying character sequence and initializes the input and output sequences according to `mode`. If `mode & ios_base::out` is true, initializes the output sequence such that `pbase()` points to the first underlying character, `epptr()` points one past the last underlying character, and `pptr()` is equal to `epptr()` if `mode & ios_base::in` is true, otherwise `pptr()` is equal to `pbase()`. If `mode & ios_base::in` is true, initializes the input sequence such that `eback()` and `gptr()` point to the first underlying character and `egptr()` points one past the last underlying character.

> -3- Postconditions: If `mode & ios_base::out` is true, `pbase()` points to the first underlying character and `(epptr() >= pbase() + s.size())` holds; in addition, if `mode & ios_base::in` is true, `(pptr() == pbase() + s.data())` holds, otherwise `(pptr() == pbase())` is true. If `mode & ios_base::in` is true, `eback()` points to the first underlying character, and `(gptr() == eback())` and `(egptr() == eback() + s.size())` hold.

[ Kona (2007) Moved to Ready. ]

### 563. stringbuf seeking from end

Section: 27.8.1.4 [stringbuf.virtuals] Status: CD1 Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2008-09-26

View all other issues in [stringbuf.virtuals].

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Discussion:

According to Table 92 (unchanged by issue 432), when `(way == end)` the `newoff` value in out mode is computed as the difference between `epptr()` and `pbase()`.

This value isn't meaningful unless the value of `epptr()` can be precisely controlled by a program. That used to be possible until we accepted the resolution of issue 432, but since then the requirements on `overflow()` have been relaxed to allow it to make more than 1 write position available (i.e., by setting `epptr()` to some unspecified value past `pptr()`). So after the first call to `overflow()` positioning the output sequence relative to end will have unspecified results.

In addition, in `in|out` mode, since `(egptr() == epptr())` need not hold, there are two different possible values for `newoff`: `epptr() - pbase()` and `egptr() - eback()`.

Proposed resolution:

Change the `newoff` column in the last row of Table 94 to read:

> the end high mark pointer minus the beginning pointer (`xend high_mark - xbeg`).

[ Kona (2007) Moved to Ready. ]

### 564. stringbuf seekpos underspecified

Section: 27.8.1.4 [stringbuf.virtuals] Status: WP Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2009-10-26

View all other issues in [stringbuf.virtuals].

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Discussion:

The effects of the `seekpos()` member function of `basic_stringbuf` simply say that the function positions the input and/or output sequences but fail to spell out exactly how. This is in contrast to the detail in which `seekoff()` is described.

[ 2009-07 Frankfurt ]

> Move to Ready.

Proposed resolution:

Change 27.7.1.3, p13 to read:

> -13- Effects: Equivalent to `seekoff(off_type(sp), ios_base::beg, which)`. Alters the stream position within the controlled sequences, if possible, to correspond to the stream position stored in `sp` (as described below).

> - If `(which & ios_base::in) != 0`, positions the input sequence.
> - If `(which & ios_base::out) != 0`, positions the output sequence.
> - If `sp` is an invalid stream position, or if the function positions neither sequence, the positioning operation fails. If `sp` has not been obtained by a previous successful call to one of the positioning functions (`seekoff`, `seekpos`, `tellg`, `tellp`) the effect is undefined.

[ Kona (2007): A `pos_type` is a position in a stream by definition, so there is no ambiguity as to what it means. Proposed Disposition: NAD ]

[ Post-Kona Martin adds: I'm afraid I disagree with the Kona '07 rationale for marking it NAD. The only text that describes precisely what it means to position the input or output sequence is in `seekoff()`. The `seekpos()` Effects clause is inadequate in comparison and the proposed resolution plugs the hole by specifying `seekpos()` in terms of `seekoff()`. ]

### 565. xsputn inefficient

Section: 27.6.2.4.5 [streambuf.virt.put] Status: WP Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2009-10-26

View all issues with WP status.

Discussion:

`streambuf::xsputn()` is specified to have the effect of "writing up to `n` characters to the output sequence as if by repeated calls to `sputc(c)`."

Since `sputc()` is required to call `overflow()` when `(pptr() == epptr())` is true, strictly speaking `xsputn()` should do the same. However, doing so would be suboptimal in some interesting cases, such as in unbuffered mode or when the buffer is `basic_stringbuf`.

Assuming calling `overflow()` is not really intended to be required and the wording is simply meant to describe the general effect of appending to the end of the sequence it would be worthwhile to mention in `xsputn()` that the function is not actually required to cause a call to `overflow()`.

[ 2009-07 Frankfurt ]

> Move to Ready.

Proposed resolution:

Add the following sentence to the `xsputn()` Effects clause in 27.5.2.4.5, p1 (N1804):

> -1- Effects: Writes up to `n` characters to the output sequence as if by repeated calls to `sputc(c)`. The characters written are obtained from successive elements of the array whose first element is designated by `s`. Writing stops when either `n` characters have been written or a call to `sputc(c)` would return `traits::eof()`. It is uspecified whether the function calls `overflow()` when `(pptr() == epptr())` becomes true or whether it achieves the same effects by other means.

In addition, I suggest to add a footnote to this function with the same text as Footnote 292 to make it extra clear that derived classes are permitted to override `xsputn()` for efficiency.

[ Kona (2007): We want to permit a `streambuf` that streams output directly to a device without making calls to `sputc` or `overflow`. We believe that has always been the intention of the committee. We believe that the proposed wording doesn't accomplish that. Proposed Disposition: Open ]

### 566. array forms of unformatted input function undefined for zero-element arrays

Section: 27.7.1.3 [istream.unformatted] Status: CD1 Submitter: Martin Sebor Opened: 2006-02-23 Last modified: 2008-09-26

View all other issues in [istream.unformatted].

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Discussion:

The array forms of unformatted input functions don't have well-defined semantics for zero-element arrays in a couple of cases. The affected ones (`istream::get()` and `getline()`) are supposed to terminate when `(n - 1)` characters are stored, which obviously can never be true when `(n == 0)` to start with.

Proposed resolution:

I propose the following changes (references are relative to the Working Draft (document N1804).

Change 27.6.1.3, p8 (`istream::get()`), bullet 1 as follows:

> if `(n < 1)` is true or `(n - 1)` characters are stored;

Similarly, change 27.6.1.3, p18 (`istream::getline()`), bullet 3 as follows:

> `(n < 1)` is true or `(n - 1)` characters are stored (in which case the function calls `setstate(failbit)`).

Finally, change p21 as follows:

> In any case, provided `(n > 0)` is true, it then stores a null character (using charT()) into the next successive location of the array.

### 567. streambuf inserter and extractor should be unformatted

Section: 27.7 [iostream.format] Status: CD1 Submitter: Martin Sebor Opened: 2006-02-25 Last modified: 2008-09-26

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Discussion:

Issue 60 explicitly made the extractor and inserter operators that take a `basic_streambuf*` argument formatted input and output functions, respectively. I believe that's wrong, certainly in the case of the extractor, since formatted functions begin by extracting and discarding whitespace. The extractor should not discard any characters.

Proposed resolution:

I propose to change each operator to behave as unformatted input and output function, respectively. The changes below are relative to the working draft document number N1804.

Specifically, change 27.6.1.2.3, p14 as follows:

> Effects: Behaves as an unformatted input function (as described in 27.6.1.2.1 27.6.1.3, paragraph 1).

And change 27.6.2.5.3, p7 as follows:

> Effects: Behaves as an unformatted output function (as described in 27.6.2.5.1 27.6.2.6, paragraph 1).

[ Kona (2007): Proposed Disposition: Ready ]

### 574. DR 369 Contradicts Text

Section: 27.4 [iostream.objects] Status: CD1 Submitter: Pete Becker Opened: 2006-04-18 Last modified: 2008-09-26

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Discussion:

lib.iostream.objects requires that the standard stream objects are never destroyed, and it requires that they be destroyed.

DR 369 adds words to say that we really mean for ios_base::Init objects to force construction of standard stream objects. It ends, though, with the phrase "these stream objects shall be destroyed after the destruction of dynamically ...". However, the rule for destruction is stated in the standard: "The objects are not destroyed during program execution."

Proposed resolution:

Change 27.4 [iostream.objects]/1:

> -2- The objects are constructed and the associations are established at some time prior to or during the first time an object of class `ios_base::Init` is constructed, and in any case before the body of main begins execution.290) The objects are not destroyed during program execution.291) If a translation unit includes `<iostream&t;` or explicitly constructs an `ios_base::Init` object, these stream objects shall be constructed before dynamic initialization of non-local objects defined later in that translation unit, and these stream objects shall be destroyed after the destruction of dynamically initialized non-local objects defined later in that translation unit.

[ Kona (2007): From 27.4 [iostream.objects]/2, strike the words "...and these stream objects shall be destroyed after the destruction of dynamically initialized non-local objects defined later in that translation unit." Proposed Disposition: Review ]

### 575. the specification of ~shared_ptr is MT-unfriendly, makes implementation assumptions

Section: 20.8.15.2.2 [util.smartptr.shared.dest], TR1 2.2.3.2 [tr.util.smartptr.shared.dest] Status: CD1 Submitter: Peter Dimov Opened: 2006-04-23 Last modified: 2008-09-26

View all other issues in [util.smartptr.shared.dest].

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Discussion:

[tr.util.smartptr.shared.dest] says in its second bullet:

"If *this shares ownership with another shared_ptr instance (use_count() > 1), decrements that instance's use count."

The problem with this formulation is that it presupposes the existence of an "use count" variable that can be decremented and that is part of the state of a shared_ptr instance (because of the "that instance's use count".)

This is contrary to the spirit of the rest of the specification that carefully avoids to require an use count variable. Instead, use_count() is specified to return a value, a number of instances.

In multithreaded code, the usual implicit assumption is that a shared variable should not be accessed by more than one thread without explicit synchronization, and by introducing the concept of an "use count" variable, the current wording implies that two shared_ptr instances that share ownership cannot be destroyed simultaneously.

In addition, if we allow the interpretation that an use count variable is part of shared_ptr's state, this would lead to other undesirable consequences WRT multiple threads. For example,

>     p1 = p2;

would now visibly modify the state of p2, a "write" operation, requiring a lock.

Proposed resolution:

Change the first two bullets of [lib.util.smartptr.shared.dest]/1 to:

> - If `*this` is empty or shares ownership with another `shared_ptr` instance (`use_count() > 1`), there are no side effects.
> - If `*this` shares ownership with another `shared_ptr` instance (`use_count() > 1`), decrements that instance's use count.

Add the following paragraph after [lib.util.smartptr.shared.dest]/1:

> [Note: since the destruction of `*this` decreases the number of instances in `*this`'s ownership group by one, all `shared_ptr` instances that share ownership with `*this` will report an `use_count()` that is one lower than its previous value after `*this` is destroyed. --end note]

### 576. find_first_of is overconstrained

Section: 25.2.7 [alg.find.first.of] Status: CD1 Submitter: Doug Gregor Opened: 2006-04-25 Last modified: 2008-09-26

View all other issues in [alg.find.first.of].

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Discussion:

In 25.1.4 Find First [lib.alg.find.first], the two iterator type parameters to find_first_of are specified to require Forward Iterators, as follows:

>     template<class ForwardIterator1, class ForwardIterator2>
>       ForwardIterator1
>       find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
>                             ForwardIterator2 first2, ForwardIterator2 last2);
>     template<class ForwardIterator1, class ForwardIterator2,
>                       class BinaryPredicate>
>     ForwardIterator1
>       find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
>                              ForwardIterator2 first2, ForwardIterator2 last2,
>                             BinaryPredicate pred);

However, ForwardIterator1 need not actually be a Forward Iterator; an Input Iterator suffices, because we do not need the multi-pass property of the Forward Iterator or a true reference.

Proposed resolution:

Change the declarations of `find_first_of` to:

>     template<class ForwardIterator1InputIterator1, class ForwardIterator2>
>       ForwardIterator1InputIterator1
>       find_first_of(ForwardIterator1InputIterator1 first1, ForwardIterator1InputIterator1 last1,
>                             ForwardIterator2 first2, ForwardIterator2 last2);
>     template<class ForwardIterator1InputIterator1, class ForwardIterator2,
>                       class BinaryPredicate>
>     ForwardIterator1InputIterator1
>       find_first_of(ForwardIterator1InputIterator1 first1, ForwardIterator1InputIterator1 last1,
>                              ForwardIterator2 first2, ForwardIterator2 last2,
>                             BinaryPredicate pred);

### 577. upper_bound(first, last, ...) cannot return last

Section: 25.4.3.2 [upper.bound] Status: CD1 Submitter: Seungbeom Kim Opened: 2006-05-03 Last modified: 2008-09-26

View all issues with CD1 status.

Discussion:

ISO/IEC 14882:2003 says:

> 25.3.3.2 upper_bound

> Returns: The furthermost iterator `i` in the range `[first, last)` such that for any iterator `j` in the range `[first, i)` the following corresponding conditions hold: `!(value < *j)` or `comp(value, *j) == false`.

From the description above, upper_bound cannot return last, since it's not in the interval [first, last). This seems to be a typo, because if value is greater than or equal to any other values in the range, or if the range is empty, returning last seems to be the intended behaviour. The corresponding interval for lower_bound is also [first, last].

Proposed resolution:

Change [lib.upper.bound]:

> Returns: The furthermost iterator `i` in the range `[first, last)]` such that for any iterator `j` in the range `[first, i)` the following corresponding conditions hold: `!(value < *j)` or `comp(value, *j) == false`.

### 578. purpose of hint to allocator::allocate()

Section: 20.8.8.1 [allocator.members] Status: CD1 Submitter: Martin Sebor Opened: 2006-05-17 Last modified: 2008-09-26

View all other issues in [allocator.members].

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Discussion:

The description of the allocator member function `allocate()` requires that the hint argument be either 0 or a value previously returned from `allocate()`. Footnote 227 further suggests that containers may pass the address of an adjacent element as this argument.

I believe that either the footnote is wrong or the normative requirement that the argument be a value previously returned from a call to `allocate()` is wrong. The latter is supported by the resolution to issue 20-004 proposed in c++std-lib-3736 by Nathan Myers. In addition, the hint is an ordinary void* and not the `pointer` type returned by `allocate()`, with the two types potentially being incompatible and the requirement impossible to satisfy.

See also c++std-lib-14323 for some more context on where this came up (again).

Proposed resolution:

Remove the requirement in 20.6.1.1, p4 that the hint be a value previously returned from `allocate()`. Specifically, change the paragraph as follows:

Requires: hint either 0 or previously obtained from member `allocate` and not yet passed to member `deallocate`. The value hint may be used by an implementation to help improve performance 223). [Note: The value hint may be used by an implementation to help improve performance. -- end note]

> [Footnote: 223)In a container member function, the address of an adjacent element is often a good choice to pass for this argument.

### 581. `flush()` not unformatted function

Section: 27.7.2.7 [ostream.unformatted] Status: CD1 Submitter: Martin Sebor Opened: 2006-06-14 Last modified: 2008-09-26

View all other issues in [ostream.unformatted].

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Discussion:

The resolution of issue 60 changed `basic_ostream::flush()` so as not to require it to behave as an unformatted output function. That has at least two in my opinion problematic consequences:

First, `flush()` now calls `rdbuf()->pubsync()` unconditionally, without regard to the state of the stream. I can't think of any reason why `flush()` should behave differently from the vast majority of stream functions in this respect.

Second, `flush()` is not required to catch exceptions from `pubsync()` or set `badbit` in response to such events. That doesn't seem right either, as most other stream functions do so.

Proposed resolution:

I propose to revert the resolution of issue 60 with respect to `flush()`. Specifically, I propose to change 27.6.2.6, p7 as follows:

Effects: Behaves as an unformatted output function (as described in 27.6.2.6, paragraph 1). If `rdbuf()` is not a null pointer, constructs a sentry object. If this object returns `true` when converted to a value of type bool the function calls `rdbuf()->pubsync()`. If that function returns -1 calls `setstate(badbit)` (which may throw `ios_base::failure` (27.4.4.3)). Otherwise, if the sentry object returns `false`, does nothing.Does not behave as an unformatted output function (as described in 27.6.2.6, paragraph 1).

[ Kona (2007): Proposed Disposition: Ready ]

### 586. string inserter not a formatted function

Section: 21.4.8.9 [string.io] Status: CD1 Submitter: Martin Sebor Opened: 2006-06-22 Last modified: 2008-09-26

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Discussion:

Section and paragraph numbers in this paper are relative to the working draft document number N2009 from 4/21/2006.

The `basic_string` extractor in 21.3.7.9, p1 is clearly required to behave as a formatted input function, as is the `std::getline()` overload for string described in p7.

However, the `basic_string` inserter described in p5 of the same section has no such requirement. This has implications on how the operator responds to exceptions thrown from `xsputn()` (formatted output functions are required to set `badbit` and swallow the exception unless `badbit` is also set in `exceptions()`; the string inserter doesn't have any such requirement).

I don't see anything in the spec for the string inserter that would justify requiring it to treat exceptions differently from all other similar operators. (If it did, I think it should be made this explicit by saying that the operator "does not behave as a formatted output function" as has been made customary by the adoption of the resolution of issue 60).

Proposed resolution:

I propose to change the Effects clause in 21.3.7.9, p5, as follows:

> Effects: Begins by constructing a sentry object k as if k were constructed by typename `basic_ostream<charT, traits>::sentry k (os)`. If `bool(k)` is `true`, Behaves as a formatted output function (27.6.2.5.1). After constructing a `sentry` object, if this object returns `true` when converted to a value of type `bool`, determines padding as described in 22.2.2.2.2, then inserts the resulting sequence of characters `seq` as if by calling `os.rdbuf()->sputn(seq , n)`, where `n` is the larger of `os.width()` and `str.size()`; then calls `os.width(0)`. If the call to sputn fails, calls `os.setstate(ios_base::failbit)`.

This proposed resilution assumes the resolution of issue 394 (i.e., that all formatted output functions are required to set `ios_base::badbit` in response to any kind of streambuf failure), and implicitly assumes that a return value of `sputn(seq, n)` other than `n` indicates a failure.

### 589. Requirements on iterators of member template functions of containers

Section: 23.2 [container.requirements] Status: CD1 Submitter: Peter Dimov Opened: 2006-08-02 Last modified: 2008-09-26

View other active issues in [container.requirements].

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Duplicate of: 536

Discussion:

There appears to be no requirements on the InputIterators used in sequences in 23.1.1 in terms of their value_type, and the requirements in 23.1.2 appear to be overly strict (requires InputIterator::value_type be the same type as the container's value_type).

Proposed resolution:

Change 23.1.1 p3:

> In Tables 82 and 83, `X` denotes a sequence class, `a` denotes a value of `X`, `i` and `j` denote iterators satisfying input iterator requirements and refer to elements implicitly convertible to `value_type`, `[i, j)` denotes a valid range, `n` denotes a value of `X::size_type`, `p` denotes a valid iterator to `a`, `q` denotes a valid dereferenceable iterator to `a`, `[q1, q2)` denotes a valid range in `a`, and `t` denotes a value of `X::value_type`.

Change 23.1.2 p7:

> In Table 84, `X` is an associative container class, `a` is a value of `X`, `a_uniq` is a value of `X` when `X` supports unique keys, and `a_eq` is a value of `X` when `X` supports multiple keys, `i` and `j` satisfy input iterator requirements and refer to elements of implicitly convertible to `value_type`, `[i, j)` is a valid range, `p` is a valid iterator to `a`, `q` is a valid dereferenceable iterator to `a`, `[q1, q2)` is a valid range in `a`, `t` is a value of `X::value_type`, `k` is a value of `X::key_type` and `c` is a value of type `X::key_compare`.

Rationale:

Concepts will probably come in and rewrite this section anyway. But just in case it is easy to fix this up as a safety net and as a clear statement of intent.

### 593. __STDC_CONSTANT_MACROS

Section: 18.4 [cstdint], TR1 8.22 [tr.c99.cstdint] Status: CD1 Submitter: Walter Brown Opened: 2006-08-28 Last modified: 2008-09-26

View all other issues in [cstdint].

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Discussion:

Clause 18.3 of the current Working Paper (N2009) deals with the new C++ headers <cstdint> and <stdint.h>. These are of course based on the C99 header <stdint.h>, and were part of TR1.

Per 18.3.1/1, these headers define a number of macros and function macros. While the WP does not mention __STDC_CONSTANT_MACROS in this context, C99 footnotes do mention __STDC_CONSTANT_MACROS. Further, 18.3.1/2 states that "The header defines all ... macros the same as C99 subclause 7.18."

Therefore, if I wish to have the above-referenced macros and function macros defined, must I #define __STDC_CONSTANT_MACROS before I #include <cstdint>, or does the C++ header define these macros/function macros unconditionally?

Proposed resolution:

To put this issue to rest for C++0X, I propose the following addition to 18.3.1/2 of the Working Paper N2009:

> [Note: The macros defined by <cstdint> are provided unconditionally: in particular, the symbols __STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS (mentioned in C99 footnotes 219, 220, and 222) play no role in C++. --end note]

### 595. TR1/C++0x: fabs(complex<T>) redundant / wrongly specified

Section: 26.4.7 [complex.value.ops] Status: CD1 Submitter: Stefan Große Pawig Opened: 2006-09-24 Last modified: 2009-03-21

View all other issues in [complex.value.ops].

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Discussion:

TR1 introduced, in the C compatibility chapter, the function fabs(complex<T>):

>     ----- SNIP -----
>     8.1.1 Synopsis                                [tr.c99.cmplx.syn]

>       namespace std {
>       namespace tr1 {
>     [...]
>       template<class T> complex<T> fabs(const complex<T>& x);
>       } // namespace tr1
>       } // namespace std

>     [...]

>     8.1.8 Function fabs                          [tr.c99.cmplx.fabs]

>     1 Effects: Behaves the same as C99 function cabs, defined in
>       subclause 7.3.8.1.
>     ----- SNIP -----

The current C++0X draft document (n2009.pdf) adopted this definition in chapter 26.3.1 (under the comment // 26.3.7 values) and 26.3.7/7.

But in C99 (ISO/IEC 9899:1999 as well as the 9899:TC2 draft document n1124), the referenced subclause reads

>     ----- SNIP -----
>     7.3.8.1 The cabs functions

>       Synopsis

>     1 #include <complex.h>
>       double cabs(double complex z);
>       float cabsf(float complex z);
>       long double cabsl(long double z);

>       Description

>     2 The cabs functions compute the complex absolute value (also called
>       norm, modulus, or magnitude) of z.

>       Returns

>     3 The cabs functions return the complex absolute value.
>     ----- SNIP -----

Note that the return type of the cabs*() functions is not a complex type. Thus, they are equivalent to the already well established template<class T> T abs(const complex<T>& x); (26.2.7/2 in ISO/IEC 14882:1998, 26.3.7/2 in the current draft document n2009.pdf).

So either the return value of fabs() is specified wrongly, or fabs() does not behave the same as C99's cabs*().

Possible Resolutions

This depends on the intention behind the introduction of fabs().

If the intention was to provide a /complex/ valued function that calculates the magnitude of its argument, this should be explicitly specified. In TR1, the categorization under "C compatibility" is definitely wrong, since C99 does not provide such a complex valued function.

Also, it remains questionable if such a complex valued function is really needed, since complex<T> supports construction and assignment from real valued arguments. There is no difference in observable behaviour between

>       complex<double> x, y;
>       y = fabs(x);
>       complex<double> z(fabs(x));

and

>       complex<double> x, y;
>       y = abs(x);
>       complex<double> z(abs(x));

If on the other hand the intention was to provide the intended functionality of C99, fabs() should be either declared deprecated or (for C++0X) removed from the standard, since the functionality is already provided by the corresponding overloads of abs().

[ Bellevue: ]

> Bill believes that abs() is a suitable overload. We should remove fabs().

Proposed resolution:

Change the synopsis in 26.4.1 [complex.syn]:

>     template<class T> complex<T> fabs(const complex<T>&);

Remove 26.4.7 [complex.value.ops], p7:

>     template<class T> complex<T> fabs(const complex<T>& x);

> > -7- Effects: Behaves the same as C99 function `cabs`, defined in subclause 7.3.8.1.

[ Kona (2007): Change the return type of `fabs(complex)` to `T`. Proposed Disposition: Ready ]

### 596. 27.8.1.3 Table 112 omits "a+" and "a+b" modes

Section: 27.9.1.4 [filebuf.members] Status: CD1 Submitter: Thomas Plum Opened: 2006-09-26 Last modified: 2008-09-26

View all other issues in [filebuf.members].

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Discussion:

In testing 27.9.1.4 [filebuf.members], Table 112 (in the latest N2009 draft), we invoke

>        ostr.open("somename", ios_base::out | ios_base::in | ios_base::app)

and we expect the open to fail, because out|in|app is not listed in Table 92, and just before the table we see very specific words:

> If mode is not some combination of flags shown in the table then the open fails.

But the corresponding table in the C standard, 7.19.5.3, provides two modes "a+" and "a+b", to which the C++ modes out|in|app and out|in|app|binary would presumably apply.

We would like to argue that the intent of Table 112 was to match the semantics of 7.19.5.3 and that the omission of "a+" and "a+b" was unintentional. (Otherwise there would be valid and useful behaviors available in C file I/O which are unavailable using C++, for no valid functional reason.)

We further request that the missing modes be explicitly restored to the WP, for inclusion in C++0x.

[ Martin adds: ]

...besides "a+" and "a+b" the C++ table is also missing a row for a lone app bit which in at least two current implementation as well as in Classic Iostreams corresponds to the C stdio "a" mode and has been traditionally documented as implying ios::out. Which means the table should also have a row for in|app meaning the same thing as "a+" already proposed in the issue.

Proposed resolution:

Add to the table "File open modes" in 27.9.1.4 [filebuf.members]:

> File open modes
> `ios_base` Flag combination | `stdio` equivalent
> --- | ---
> `binary` | `in` | `out` | `trunc` | `app` | ``
> |  | `+` |  |  | `"w"`
> |  | `+` |  | `+` | `"a"`
> |  |  |  | `+` | `"a"`
> |  | `+` | `+` |  | `"w"`
> | `+` |  |  |  | `"r"`
> | `+` | `+` |  |  | `"r+"`
> | `+` | `+` | `+` |  | `"w+"`
> | `+` | `+` |  | `+` | `"a+"`
> | `+` |  |  | `+` | `"a+"`
> `+` |  | `+` |  |  | `"wb"`
> `+` |  | `+` |  | `+` | `"ab"`
> `+` |  |  |  | `+` | `"ab"`
> `+` |  | `+` | `+` |  | `"wb"`
> `+` | `+` |  |  |  | `"rb"`
> `+` | `+` | `+` |  |  | `"r+b"`
> `+` | `+` | `+` | `+` |  | `"w+b"`
> `+` | `+` | `+` |  | `+` | `"a+b"`
> `+` | `+` |  |  | `+` | `"a+b"`

[ Kona (2007) Added proposed wording and moved to Review. ]

### 598. Decimal: Conversion to integral should truncate, not round.

Section: TRDecimal 3.2 [trdec.types.types] Status: TRDec Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2007-04-21

View all other issues in [trdec.types.types].

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Discussion:

In a private email, Daniel writes:

> I would like to ask, what where the reason for the decision to define the semantics of the integral conversion of the decimal types, namely

>     "operator long long() const;

>          Returns: Returns the result of the
>     conversion of *this to the type long long, as if
>     performed by the expression llrounddXX(*this)."

> where XX stands for either 32, 64, or 128, corresponding to the proper decimal type. The exact meaning of llrounddXX is not given in that paper, so I compared it to the corresponding definition given in C99, 2nd edition (ISO 9899), which says in 7.12.9.7 p. 2:

> "The lround and llround functions round their argument to the nearest integer value, rounding halfway cases away from zero, regardless of the current rounding direction. [..]"

> Now considering the fact that integral conversion of the usual floating-point types ("4.9 Floating-integral conversions") has truncation semantic I wonder why this conversion behaviour has not been transferred for the decimal types.

Robert comments:

Also, there is a further error in the Returns: clause for converting `decimal::decimal128` to `long long`. It currently calls `llroundd64`, not `llroundd128`.

Proposed resolution:

Change the Returns: clause in 3.2.2.4 to:

> Returns: Returns the result of the conversion of `*this` to the type `long long`, as if performed by the expression `llroundd32(*this)` while the decimal rounding direction mode [3.5.2] `FE_DEC_TOWARD_ZERO` is in effect.

Change the Returns: clause in 3.2.3.4 to:

> Returns: Returns the result of the conversion of `*this` to the type `long long`, as if performed by the expression `llroundd64(*this)` while the decimal rounding direction mode [3.5.2] `FE_DEC_TOWARD_ZERO` is in effect.

Change the Returns: clause in 3.2.4.4 to:

> Returns: Returns the result of the conversion of `*this` to the type `long long`, as if performed by the expression `llroundd64(*this)` `llroundd128(*this)` while the decimal rounding direction mode [3.5.2] `FE_DEC_TOWARD_ZERO` is in effect.

### 599. Decimal: Say "octets" instead of "bytes."

Section: TRDecimal 3.1 [trdec.types.encodings] Status: TRDec Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2007-04-21

View all issues with TRDec status.

Discussion:

Daniel writes in a private email:

> - 3.1 'Decimal type encodings' says in its note:

>     "this implies that
>     sizeof(std::decimal::decimal32) == 4,
>     sizeof(std::decimal::decimal64) == 8, and
>     sizeof(std::decimal::decimal128) == 16."

> This is a wrong assertion, because the definition of 'byte' in 1.7 'The C+ + memory model' of ISO 14882 (2nd edition) does not specify that a byte must be necessarily 8 bits large, which would be necessary to compare with the specified bit sizes of the types decimal32, decimal64, and decimal128.

Proposed resolution:

Change 3.1 as follows:

> The three decimal encoding formats defined in IEEE-754R correspond to the three decimal floating types as follows:

> - decimal32 is a decimal32 number, which is encoded in four consecutive bytes octets (32 bits)
> - decimal64 is a decimal64 number, which is encoded in eight consecutive bytes octets (64 bits)
> - decimal128 is a decimal128 number, which is encoded in 16 consecutive bytes octets (128 bits)

> [Note: this implies that `sizeof(std::decimal::decimal32) == 4`, `sizeof(std::decimal::decimal64) == 8`, and `sizeof(std::decimal::decimal128) == 16`. --end note]

### 600. Decimal: Wrong parameters for wcstod* functions

Section: TRDecimal 3.9 [trdec.types.cwchar] Status: TRDec Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2007-04-21

View all issues with TRDec status.

Discussion:

Daniel writes:

> - 3.9.1 'Additions to <cwchar>' provides wrong signatures to the wcstod32, wcstod64, and wcstod128 functions ([the parameters have type pointer-to-] char instead of wchar_t).

Proposed resolution:

Change "3.9.1 Additions to `<cwchar>` synopsis" to:

           namespace std {
           namespace decimal {
             // 3.9.2 wcstod functions:
             decimal32  wcstod32  (const char wchar_t * nptr, char wchar_t ** endptr);
             decimal64  wcstod64  (const char wchar_t * nptr, char wchar_t ** endptr);
             decimal128 wcstod128 (const char wchar_t * nptr, char wchar_t ** endptr);
           }
           }

### 601. Decimal: numeric_limits typos

Section: TRDecimal 3.3 [trdec.types.limits] Status: TRDec Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2007-04-21

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Discussion:

Daniel writes in a private email:

> - 3.3 'Additions to header <limits>' contains two errors in the specialisation of numeric_limits<decimal::decimal128>:

> 1. The static member max() returns DEC128_MIN, this should be DEC128_MAX.
> 2. The static member digits is assigned to 384, this should be 34 (Probably mixed up with the max. exponent for decimal::decimal64).

Proposed resolution:

In "3.3 Additions to header `<limits>`" change numeric_limits<decimal::decimal128> as follows:

            template<> class numeric_limits<decimal::decimal128> {
              public:
                static const bool is_specialized = true;

                static decimal::decimal128 min() throw() { return DEC128_MIN; }
                static decimal::decimal128 max() throw() { return DEC128_MIN; DEC128_MAX; }

                static const int digits       = 384 34;
                /* ... */

### 602. Decimal: "generic floating type" not defined.

Section: TRDecimal 3 [trdec.types] Status: TRDec Submitter: Daniel Krugler Opened: 2006-05-28 Last modified: 2007-04-21

View all other issues in [trdec.types].

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Discussion:

The document uses the term "generic floating types," but defines it nowhere.

Proposed resolution:

Change the first paragraph of "3 Decimal floating-point types" as follows:

> This Technical Report introduces three decimal floating-point types, named decimal32, decimal64, and decimal128. The set of values of type decimal32 is a subset of the set of values of type decimal64; the set of values of the type decimal64 is a subset of the set of values of the type decimal128. Support for decimal128 is optional. These types supplement the Standard C++ types `float`, `double`, and `long double`, which are collectively described as the basic floating types.

### 603. Decimal: Trivially simplifying decimal classes.

Section: TRDecimal 3 [trdec.types] Status: TRDec Submitter: Martin Sebor Opened: 2006-05-28 Last modified: 2007-04-21

View all other issues in [trdec.types].

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Discussion:

In c++std-lib-17198, Martin writes:

> Each of the three classes proposed in the paper (decimal32, decimal64, and decimal128) explicitly declares and specifies the semantics of its copy constructor, copy assignment operator, and destructor. Since the semantics of all three functions are identical to the trivial versions implicitly generated by the compiler in the absence of any declarations it is safe to drop them from the spec. This change would make the proposed classes consistent with other similar classes already in the standard (e.g., std::complex).

Proposed resolution:

Change "3.2.2 Class `decimal32`" as follows:

          namespace std {
          namespace decimal {
            class decimal32 {
              public:
                // 3.2.2.1 construct/copy/destroy:
                decimal32();
                decimal32(const decimal32 & d32);
                decimal32 & operator=(const decimal32 & d32);
                ~decimal32();
                /* ... */

Change "3.2.2.1 construct/copy/destroy" as follows:

            decimal32();

        Effects: Constructs an object of type decimal32 with the value 0;

            decimal32(const decimal32 & d32);
            decimal32 & operator=(const decimal32 & d32);

        Effects: Copies an object of type decimal32.

            ~decimal32();

        Effects: Destroys an object of type decimal32.

Change "3.2.3 Class `decimal64`" as follows:

          namespace std {
          namespace decimal {
            class decimal64 {
              public:
                // 3.2.3.1 construct/copy/destroy:
                decimal64();
                decimal64(const decimal64 & d64);
                decimal64 & operator=(const decimal64 & d64);
                ~decimal64();
                /* ... */

Change "3.2.3.1 construct/copy/destroy" as follows:

            decimal64();

        Effects: Constructs an object of type decimal64 with the value 0;

            decimal64(const decimal64 & d64);
            decimal64 & operator=(const decimal64 & d64);

        Effects: Copies an object of type decimal64.

            ~decimal64();

        Effects: Destroys an object of type decimal64.

Change "3.2.4 Class `decimal128`" as follows:

          namespace std {
          namespace decimal {
            class decimal128 {
              public:
                // 3.2.4.1 construct/copy/destroy:
                decimal128();
                decimal128(const decimal128 & d128);
                decimal128 & operator=(const decimal128 & d128);
                ~decimal128();
                /* ... */

Change "3.2.4.1 construct/copy/destroy" as follows:

            decimal128();

        Effects: Constructs an object of type decimal128 with the value 0;

            decimal128(const decimal128 & d128);
            decimal128 & operator=(const decimal128 & d128);

        Effects: Copies an object of type decimal128.

            ~decimal128();

        Effects: Destroys an object of type decimal128.

### 604. Decimal: Storing a reference to a facet unsafe.

Section: TRDecimal 3 [trdec.types] Status: TRDec Submitter: Martin Sebor Opened: 2006-05-28 Last modified: 2007-07-25

View all other issues in [trdec.types].

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Discussion:

In c++std-lib-17197, Martin writes:

> The extended_num_get and extended_num_put facets are designed to store a reference to a num_get or num_put facet which the extended facets delegate the parsing and formatting of types other than decimal. One form of the extended facet's ctor (the default ctor and the size_t overload) obtains the reference from the global C++ locale while the other form takes this reference as an argument.

> The problem with storing a reference to a facet in another object (as opposed to storing the locale object in which the facet is installed) is that doing so bypasses the reference counting mechanism designed to prevent a facet that is still being referenced (i.e., one that is still installed in some locale) from being destroyed when another locale that contains it is destroyed. Separating a facet reference from the locale it comes from van make it cumbersome (and in some cases might even make it impossible) for programs to prevent invalidating the reference. (The danger of this design is highlighted in the paper.)

> This problem could be easily avoided by having the extended facets store a copy of the locale from which they would extract the base facet either at construction time or when needed. To make it possible, the forms of ctors of the extended facets that take a reference to the base facet would need to be changed to take a locale argument instead.

Proposed resolution:

1. Change the `extended_num_get` synopsis in 3.10.2 as follows:

                extended_num_get(const std::num_get<charT, InputIterator> std::locale & b, size_t refs = 0);

                /* ... */

                // const std::num_get<charT, InputIterator> & base;        exposition only
                // std::locale baseloc;                                    exposition only

2. Change the description of the above constructor in 3.10.2.1:

                extended_num_get(const std::num_get<charT, InputIterator> std::locale & b, size_t refs = 0);

> Effects: Constructs an `extended_num_get` facet as if by:

>            extended_num_get(const std::num_get<charT, InputIterator> std::locale & b, size_t refs = 0)
>                     : facet(refs), baseloc(b)
>                     { /* ... */ }

> Notes: Care must be taken by the implementation to ensure that the lifetime of the facet referenced by base exceeds that of the resulting `extended_num_get` facet.

3. Change the Returns: clause for `do_get(iter_type, iter_type, ios_base &, ios_base::iostate &, bool &) const`, et al to

> Returns: `base std::use_facet<std::num_get<charT, InputIterator> >(baseloc).get(in, end, str, err, val)`.

4. Change the `extended_num_put` synopsis in 3.10.3 as follows:

                extended_num_put(const std::num_put<charT, OutputIterator> std::locale & b, size_t refs = 0);

                /* ... */

                // const std::num_put<charT, OutputIterator> & base;       exposition only
                // std::locale baseloc;                                    exposition only

5. Change the description of the above constructor in 3.10.3.1:

                extended_num_put(const std::num_put<charT, OutputIterator> std::locale & b, size_t refs = 0);

> Effects: Constructs an `extended_num_put` facet as if by:

>            extended_num_put(const std::num_put<charT, OutputIterator> std::locale & b, size_t refs = 0)
>                     : facet(refs), baseloc(b)
>                     { /* ... */ }

> Notes: Care must be taken by the implementation to ensure that the lifetime of the facet referenced by base exceeds that of the resulting `extended_num_put` facet.

6. Change the Returns: clause for `do_put(iter_type, ios_base &, char_type, bool &) const`, et al to

> Returns: `base std::use_facet<std::num_put<charT, OutputIterator> >(baseloc).put(s, f, fill, val)`.

[ Redmond: We would prefer to rename "extended" to "decimal". ]

### 605. Decimal: <decfloat.h> doesn't live here anymore.

Section: TRDecimal 3.4 [trdec.types.cdecfloat] Status: TRDec Submitter: Robert Klarer Opened: 2006-10-17 Last modified: 2007-04-21

View all issues with TRDec status.

Discussion:

In Berlin, WG14 decided to drop the <decfloat.h> header. The contents of that header have been moved into <float.h>. For the sake of C compatibility, we should make corresponding changes.

Proposed resolution:

1. Change the heading of subclause 3.4, "Headers `<cdecfloat>` and `<decfloat.h>`" to "Additions to headers `<cfloat>` and `<float.h>`."

2. Change the text of subclause 3.4 as follows:

> The standard C++ headers `<cfloat>` and `<float.h>` define characteristics of the floating-point types `float`, `double`, and `long double`. Their contents remain unchanged by this Technical Report.

> Headers `<cdecfloat>` and `<decfloat.h>` define characteristics of the decimal floating-point types `decimal32`, `decimal64`, and `decimal128`. As well, `<decfloat.h>` defines the convenience typedefs `_Decimal32`, `_Decimal64`, and `_Decimal128`, for compatibilty with the C programming language.

> The header `<cfloat>` is described in [tr.c99.cfloat]. The header `<float.h>` is described in [tr.c99.floath]. These headers are extended by this Technical Report to define characteristics of the decimal floating-point types `decimal32`, `decimal64`, and `decimal128`. As well, `<float.h>` is extended to define the convenience typedefs `_Decimal32`, `_Decimal64`, and `_Decimal128` for compatibility with the C programming language.

3. Change the heading of subclause 3.4.1, "Header `<cdecfloat>` synopsis" to "Additions to header `<cfloat>` synopsis."

4. Change the heading of subclause 3.4.2, "Header `<decfloat.h>` synopsis" to "Additions to header `<float.h>` synopsis."

5. Change the contents of 3.4.2 as follows:

          #include <cdecfloat>

          // C-compatibility convenience typedefs:

          typedef std::decimal::decimal32  _Decimal32;
          typedef std::decimal::decimal64  _Decimal64;
          typedef std::decimal::decimal128 _Decimal128;

### 607. Concern about short seed vectors

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 Submitter: Charles Karney Opened: 2006-10-26 Last modified: 2008-09-26

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Discussion:

Short seed vectors of 32-bit quantities all result in different states. However this is not true of seed vectors of 16-bit (or smaller) quantities. For example these two seeds

>     unsigned short seed = {1, 2, 3};
>     unsigned short seed = {1, 2, 3, 0};

both pack to

>     unsigned seed = {0x20001, 0x3};

yielding the same state.

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 608. Unclear seed_seq construction details

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 Submitter: Charles Karney Opened: 2006-10-26 Last modified: 2008-09-26

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Discussion:

In 26.4.7.1 [rand.util.seedseq] /6, the order of packing the inputs into b and the treatment of signed quantities is unclear. Better to spell it out.

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 609. missing static const

Section: 26.5.4.2 [rand.adapt.ibits], TR1 5.1 [tr.rand] Status: CD1 Submitter: Walter E. Brown Opened: 2006-11-02 Last modified: 2008-09-26

View all issues with CD1 status.

Discussion:

In preparing N2111, an error on my part resulted in the omission of the following line from the template synopsis in the cited section:

>     static const size_t word_size = w;

(This same constant is found, for example, in 26.4.3.3 [rand.eng.sub].)

Proposed resolution:

Add the above declaration as the first line after the comment in [rand.adapt.ibits] p4:

>     // engine characteristics
>     static const size_t word_size = w;

and accept my apologies for the oversight.

### 610. Suggested non-normative note for C++0x

Section: 20.7.15.2.1 [func.wrap.func.con], TR1 3.7.2.1 [tr.func.wrap.func.con] Status: CD1 Submitter: Scott Meyers Opened: 2006-11-02 Last modified: 2008-09-26

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Discussion:

My suggestion is that implementers of both tr1::function and its official C++0x successor be explicitly encouraged (but not required) to optimize for the cases mentioned above, i.e., function pointers and small function objects. They could do this by using a small internal buffer akin to the buffer used by implementations of the small string optimization. (That would make this the small functor optimization -- SFO :-}) The form of this encouragement could be a note in the standard akin to footnote 214 of the current standard.

Dave Abrahams notes:

"shall not throw exceptions" should really be "nothing," both to be more grammatical and to be consistent with existing wording in the standard.

Doug Gregor comments: I think this is a good idea. Currently, implementations of tr1::function are required to have non-throwing constructors and assignment operators when the target function object is a function pointer or a reference_wrapper. The common case, however, is for a tr1::function to store either an empty function object or a member pointer + an object pointer.

The function implementation in the upcoming Boost 1.34.0 uses the "SFO", so that the function objects for typical bind expressions like

>     bind(&X::f, this, _1, _2, _3)

do not require heap allocation when stored in a boost::function. I believe Dinkumware's implementation also performs this optimization.

Proposed resolution:

Revise 20.5.14.2.1 p6 [func.wrap.func.con] to add a note as follows:

> Throws: shall not throw exceptions if `f`'s target is a function pointer or a function object passed via `reference_wrapper`. Otherwise, may throw `bad_alloc` or any exception thrown by the copy constructor of the stored function object.

> Note: Implementations are encouraged to avoid the use of dynamically allocated memory for "small" function objects, e.g., where `f`'s target is an object holding only a pointer or reference to an object and a member function pointer (a "bound member function").

### 611. Standard library templates and incomplete types

Section: 17.6.3.8 [res.on.functions] Status: CD1 Submitter: Nicola Musatti Opened: 2006-11-13 Last modified: 2008-09-26

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Discussion:

In the latest available draft standard (N2134) § 17.4.3.6 [res.on.functions] states:

> -1- In certain cases (replacement functions, handler functions, operations on types used to instantiate standard library template components), the C++ Standard Library depends on components supplied by a C++ program. If these components do not meet their requirements, the Standard places no requirements on the implementation.

> -2- In particular, the effects are undefined in the following cases:

> [...]

> - if an incomplete type (3.9) is used as a template argument when instantiating a template component.

This is contradicted by § 20.6.6.2/2 [util.smartptr.shared] which states:

> [...]

> The template parameter `T` of `shared_ptr` may be an incomplete type.

Proposed resolution:

Modify the last bullet of § 17.4.3.6/2 [res.on.functions] to allow for exceptions:

> - if an incomplete type (3.9) is used as a template argument when instantiating a template component, unless specifically allowed for the component.

### 612. numeric_limits::is_modulo insufficiently defined

Section: 18.3.1.2 [numeric.limits.members] Status: CD1 Submitter: Chris Jefferson Opened: 2006-11-10 Last modified: 2008-09-26

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Discussion:

18.2.1.2 55 states that "A type is modulo if it is possible to add two positive numbers together and have a result that wraps around to a third number that is less". This seems insufficient for the following reasons:

1. Doesn't define what that value received is.
2. Doesn't state the result is repeatable
3. Doesn't require that doing addition, subtraction and other operations on all values is defined behaviour.

[ Batavia: Related to N2144. Pete: is there an ISO definition of modulo? Underflow on signed behavior is undefined. ]

[ Bellevue: accept resolution, move to ready status. Does this mandate that is_modulo be true on platforms for which int happens to b modulo? A: the standard already seems to require that. ]

Proposed resolution:

Suggest 18.3.1.2 [numeric.limits.members], paragraph 57 is amended to:

> A type is modulo if, it is possible to add two positive numbers and have a result that wraps around to a third number that is less. given any operation involving +,- or * on values of that type whose value would fall outside the range `[min(), max()]`, then the value returned differs from the true value by an integer multiple of `(max() - min() + 1)`.

### 613. max_digits10 missing from numeric_limits

Section: 18.3.1.5 [numeric.special] Status: CD1 Submitter: Bo Persson Opened: 2006-11-20 Last modified: 2008-09-26

View all other issues in [numeric.special].

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Discussion:

Section 18.3.1.5 [numeric.special] starts out by saying that "All members shall be provided for all specializations."

Then it goes on to show specializations for float and bool, where one member is missing (max_digits10).

Maarten Kronenburg adds:

I agree, just adding the comment that the exact number of decimal digits is digits * ln(radix) / ln(10), where probably this real number is rounded downward for digits10, and rounded upward for max_digits10 (when radix=10, then digits10=max_digits10). Why not add this exact definition also to the standard, so the user knows what these numbers exactly mean.

Howard adds:

For reference, here are the correct formulas from N1822:

>     digits10 = floor((digits-1) * log10(2))
>     max_digits10 = ceil((1 + digits) * log10(2))

We are also missing a statement regarding for what specializations this member has meaning.

Proposed resolution:

Change and add after 18.3.1.2 [numeric.limits.members], p11:

>     static const int max_digits10;

> > -11- Number of base 10 digits required to ensure that values which differ by only one epsilon are always differentiated.

> > -12- Meaningful for all floating point types.

Change 18.3.1.5 [numeric.special], p2:

>     template<> class numeric_limits<float> {
>     public:
>       static const bool is_specialized = true;
>       ...
>       static const int digits10 = 6;
>       static const int max_digits10 = 9;
>       ...

Change 18.3.1.5 [numeric.special], p3:

>     template<> class numeric_limits<bool> {
>     public:
>       static const bool is_specialized = true;
>       ...
>       static const int digits10 = 0;
>       static const int max_digits10 = 0;
>       ...

### 616. missing 'typename' in ctype_byname

Section: 22.4.1.2 [locale.ctype.byname] Status: CD1 Submitter: Bo Persson Opened: 2006-12-16 Last modified: 2008-09-26

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Discussion:

Section 22.2.1.2 defines the ctype_byname class template. It contains the line

>     typedef ctype<charT>::mask   mask;

Proposed resolution:

as this is a dependent type, it should obviously be

>     typedef typename ctype<charT>::mask   mask;

### 618. valarray::cshift() effects on empty array

Section: 26.6.2.7 [valarray.members] Status: CD1 Submitter: Gabriel Dos Reis Opened: 2007-01-10 Last modified: 2008-09-26

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Discussion:

I would respectfully request an issue be opened with the intention to clarify the wording for `size() == 0` for `cshift`.

Proposed resolution:

Change 26.6.2.7 [valarray.members], paragraph 10:

>     valarray<T> cshift(int n) const;

> > This function returns an object of class `valarray<T>`, of length `size()`, each of whose elements `I` is `(*this)[(I + n ) % size()]`. Thus, if element zero is taken as the leftmost element, a positive value of n shifts the elements circularly left n places. that is a circular shift of `*this`. If element zero is taken as the leftmost element, a non-negative value of n shifts the elements circularly left n places and a negative value of n shifts the elements circularly right -n places.

Rationale:

We do not believe that there is any real ambiguity about what happens when `size() == 0`, but we do believe that spelling this out as a C++ expression causes more trouble that it solves. The expression is certainly wrong when `n < 0`, since the sign of % with negative arguments is implementation defined.

[ Kona (2007) Changed proposed wording, added rationale and set to Review. ]

### 619. Longjmp wording problem

Section: 18.10 [support.runtime] Status: CD1 Submitter: Lawrence Crowl Opened: 2007-01-12 Last modified: 2008-09-26

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Discussion:

The wording for `longjmp` is confusing.

18.10 [support.runtime] -4- Other runtime support

> The function signature `longjmp(jmp_buf jbuf, int val)` has more restricted behavior in this International Standard. If any automatic objects would be destroyed by a thrown exception transferring control to another (destination) point in the program, then a call to `longjmp(jbuf, val)` that the throw point that transfers control to the same (destination) point has undefined behavior.

Someone at Google thinks that should say "then a call to `longjmp(jbuf, val)` *at* the throw point that transfers control".

Bill Gibbons thinks it should say something like "If any automatic objects would be destroyed by an exception thrown at the point of the longjmp and caught only at the point of the setjmp, the behavior is undefined."

Proposed resolution:

In general, accept Bill Gibbons' recommendation, but add "call" to indicate that the undefined behavior comes from the dynamic call, not from its presence in the code. In 18.10 [support.runtime] paragraph 4, change

> The function signature `longjmp(jmp_buf jbuf, int val)` has more restricted behavior in this International Standard. If any automatic objects would be destroyed by a thrown exception transferring control to another (destination) point in the program, then a call to `longjmp(jbuf, val)` that the throw point that transfers control to the same (destination) point has undefined behavior. A `setjmp`/`longjmp` call pair has undefined behavior if replacing the `setjmp` and `longjmp` by `catch` and `throw` would destroy any automatic objects.

### 620. valid uses of empty valarrays

Section: 26.6.2.1 [valarray.cons] Status: CD1 Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2008-09-26

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Discussion:

The Effects clause for the default `valarray` ctor suggests that it is possible to increase the size of an empty `valarray` object by calling other non-const member functions of the class besides `resize()`. However, such an interpretation would be contradicted by the requirement on the copy assignment operator (and apparently also that on the computed assignments) that the assigned arrays be the same size. See the reflector discussion starting with c++std-lib-17871.

In addition, Footnote 280 uses some questionable normative language.

Proposed resolution:

Reword the Effects clause and Footnote 280 as follows (26.6.2.1 [valarray.cons]):

> `valarray();`

> Effects: Constructs an object of class `valarray<T>`,279) which has zero length until it is passed into a library function as a modifiable lvalue or through a non-constant this pointer.280)

> Postcondition: `size() == 0`.

> Footnote 280: This default constructor is essential, since arrays of `valarray` are likely to prove useful. There shall also be a way to change the size of an array after initialization; this is supplied by the semantics may be useful. The length of an empty array can be increased after initialization by means of the `resize()` member function.

### 621. non-const copy assignment operators of helper arrays

Section: 26.6 [numarray] Status: CD1 Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2008-09-26

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Discussion:

The computed and "fill" assignment operators of `valarray` helper array class templates (`slice_array`, `gslice_array`, `mask_array`, and `indirect_array`) are const member functions of each class template (the latter by the resolution of 123 since they have reference semantics and thus do not affect the state of the object on which they are called. However, the copy assignment operators of these class templates, which also have reference semantics, are non-const. The absence of constness opens the door to speculation about whether they really are intended to have reference semantics (existing implementations vary widely).

Pre-Kona, Martin adds:

I realized that adding the const qualifier to the functions as I suggested would break the const correctness of the classes. A few possible solutions come to mind:

1. Add the const qualifier to the return types of these functions.
2. Change the return type of all the functions to void to match the signatures of all the other assignment operators these classes define.
3. Prohibit the copy assignment of these classes by declaring the copy assignment operators private (as is done and documented by some implementations).

Proposed resolution:

Declare the copy assignment operators of all four helper array class templates const.

Specifically, make the following edits:

Change the signature in 26.6.5 [template.slice.array] and 26.6.5.1 [slice.arr.assign] as follows:

>     const slice_array& operator= (const slice_array&) const;

Change the signature in 26.6.7 [template.gslice.array] and 26.6.7.1 [gslice.array.assign] as follows:

>     const gslice_array& operator= (const gslice_array&) const;

Change the signature in 26.6.8 [template.mask.array] and 26.6.8.1 [mask.array.assign] as follows:

>     const mask_array& operator= (const mask_array&) const;

Change the signature in 26.6.9 [template.indirect.array] and 26.6.9.1 [indirect.array.assign] as follows:

>     const indirect_array& operator= (const indirect_array&) const;

[ Kona (2007) Added const qualification to the return types and set to Ready. ]

### 622. behavior of `filebuf` dtor and `close` on error

Section: 27.9.1.17 [fstream.members] Status: CD1 Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2008-09-26

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Discussion:

`basic_filebuf` dtor is specified to have the following straightforward effects:

> Effects: Destroys an object of class `basic_filebuf`. Calls `close()`.

`close()` does a lot of potentially complicated processing, including calling `overflow()` to write out the termination sequence (to bring the output sequence to its initial shift state). Since any of the functions called during the processing can throw an exception, what should the effects of an exception be on the dtor? Should the dtor catch and swallow it or should it propagate it to the caller? The text doesn't seem to provide any guidance in this regard other than the general restriction on throwing (but not propagating) exceptions from destructors of library classes in 17.6.4.11 [res.on.exception.handling].

Further, the last thing `close()` is specified to do is call `fclose()` to close the `FILE` pointer. The last sentence of the Effects clause reads:

> ... If any of the calls to `overflow` or `std::fclose` fails then `close` fails.

This suggests that `close()` might be required to call `fclose()` if and only if none of the calls to `overflow()` fails, and avoid closing the `FILE` otherwise. This way, if `overflow()` failed to flush out the data, the caller would have the opportunity to try to flush it again (perhaps after trying to deal with whatever problem may have caused the failure), rather than losing it outright.

On the other hand, the function's Postcondition specifies that `is_open() == false`, which suggests that it should call `fclose()` unconditionally. However, since Postcondition clauses are specified for many functions in the standard, including constructors where they obviously cannot apply after an exception, it's not clear whether this Postcondition clause is intended to apply even after an exception.

It might be worth noting that the traditional behavior (Classic Iostreams `fstream::close()` and C `fclose()`) is to close the `FILE` unconditionally, regardless of errors.

[ See 397 and 418 for related issues. ]

Proposed resolution:

After discussing this on the reflector (see the thread starting with c++std-lib-17650) we propose that `close()` be clarified to match the traditional behavior, that is to close the `FILE` unconditionally, even after errors or exceptions. In addition, we propose the dtor description be amended so as to explicitly require it to catch and swallow any exceptions thrown by `close()`.

Specifically, we propose to make the following edits in 27.9.1.4 [filebuf.members]:

>     basic_filebuf<charT,traits>* close();

> Effects: If `is_open() == false`, returns a null pointer. If a put area exists, calls `overflow(traits::eof())` to flush characters. If the last virtual member function called on `*this` (between `underflow`, `overflow`, `seekoff`, and `seekpos`) was `overflow` then calls `a_codecvt.unshift` (possibly several times) to determine a termination sequence, inserts those characters and calls `overflow(traits::eof())` again. Finally, regardless of whether any of the preceding calls fails or throws an exception, the function it closes the file ("as if" by calling `std::fclose(file)`).334) If any of the calls made by the function to `overflow` or, including `std::fclose`, fails then `close` fails by returning a null pointer. If one of these calls throws an exception, the exception is caught and rethrown after closing the file.

And to make the following edits in 27.9.1.2 [filebuf.cons].

>     virtual ~basic_filebuf();

> Effects: Destroys an object of class `basic_filebuf<charT,traits>`. Calls `close()`. If an exception occurs during the destruction of the object, including the call to `close()`, the exception is caught but not rethrown (see 17.6.4.11 [res.on.exception.handling]).

### 623. `pubimbue` forbidden to call `imbue`

Section: 27.2.1 [iostream.limits.imbue] Status: CD1 Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2008-09-26

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Discussion:

27.2.1 [iostream.limits.imbue] specifies that "no function described in clause 27 except for `ios_base::imbue` causes any instance of `basic_ios::imbue` or `basic_streambuf::imbue` to be called."

That contradicts the Effects clause for `basic_streambuf::pubimbue()` which requires the function to do just that: call `basic_streambuf::imbue()`.

Proposed resolution:

To fix this, rephrase the sentence above to allow `pubimbue` to do what it was designed to do. Specifically. change 27.2.1 [iostream.limits.imbue], p1 to read:

> No function described in clause 27 except for `ios_base::imbue` and `basic_filebuf::pubimbue` causes any instance of `basic_ios::imbue` or `basic_streambuf::imbue` to be called. ...

### 624. `valarray` assignment and arrays of unequal length

Section: 26.6.2.2 [valarray.assign] Status: CD1 Submitter: Martin Sebor Opened: 2007-01-20 Last modified: 2008-09-26

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Discussion:

The behavior of the `valarray` copy assignment operator is defined only when both sides have the same number of elements and the spec is explicit about assignments of arrays of unequal lengths having undefined behavior.

However, the generalized subscripting assignment operators overloaded on `slice_array` et al (26.6.2.2 [valarray.assign]) don't have any such restriction, leading the reader to believe that the behavior of these overloads is well defined regardless of the lengths of the arguments.

For example, based on the reading of the spec the behavior of the snippet below can be expected to be well-defined:

        const std::slice from_0_to_3 (0, 3, 1);   // refers to elements 0, 1, 2
        const std::valarray<int> a (1, 3);        // a = { 1, 1, 1 }
        std::valarray<int>       b (2, 4);        // b = { 2, 2, 2, 2 }

        b = a [from_0_to_3];

In practice, `b` may end up being `{ 1, 1, 1 }`, `{ 1, 1, 1, 2 }`, or anything else, indicating that existing implementations vary.

Quoting from Section 3.4, Assignment operators, of Al Vermeulen's Proposal for Standard C++ Array Classes (see c++std-lib-704; N0308):

> ...if the size of the array on the right hand side of the equal sign differs from the size of the array on the left, a run time error occurs. How this error is handled is implementation dependent; for compilers which support it, throwing an exception would be reasonable.

And see more history in N0280.

It has been argued in discussions on the committee's reflector that the semantics of all `valarray` assignment operators should be permitted to be undefined unless the length of the arrays being assigned is the same as the length of the one being assigned from. See the thread starting at c++std-lib-17786.

In order to reflect such views, the standard must specify that the size of the array referred to by the argument of the assignment must match the size of the array under assignment, for example by adding a Requires clause to 26.6.2.2 [valarray.assign] as follows:

> Requires: The length of the array to which the argument refers equals `size()`.

Note that it's far from clear that such leeway is necessary in order to implement `valarray` efficiently.

Proposed resolution:

Insert new paragraph into 26.6.2.2 [valarray.assign]:

>     valarray<T>& operator=(const slice_array<T>&);
>     valarray<T>& operator=(const gslice_array<T>&);
>     valarray<T>& operator=(const mask_array<T>&);
>     valarray<T>& operator=(const indirect_array<T>&);

> > Requires: The length of the array to which the argument refers equals `size()`.

> > These operators allow the results of a generalized subscripting operation to be assigned directly to a `valarray`.

### 628. Inconsistent definition of basic_regex constructor

Section: 28.8 [re.regex] Status: CD1 Submitter: Bo Persson Opened: 2007-01-23 Last modified: 2008-09-26

View all other issues in [re.regex].

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Discussion:

Section 28.8 [re.regex] lists a constructor

>     template<class InputIterator>
>     basic_regex(InputIterator first, InputIterator last,
>                            flag_type f = regex_constants::ECMAScript);

However, in section 28.8.2 [re.regex.construct], this constructor takes a pair of `ForwardIterator`.

Proposed resolution:

Change 28.8.2 [re.regex.construct]:

>     template <class ForwardIterator InputIterator>
>       basic_regex(ForwardIterator InputIterator first, ForwardIterator InputIterator last,
>                   flag_type f = regex_constants::ECMAScript);

### 629. complex insertion and locale dependence

Section: 26.4.6 [complex.ops] Status: CD1 Submitter: Gabriel Dos Reis Opened: 2007-01-28 Last modified: 2008-09-26

View all other issues in [complex.ops].

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Discussion:

is there an issue opened for (0,3) as complex number with the French local? With the English local, the above parses as an imaginery complex number. With the French locale it parses as a real complex number.

Further notes/ideas from the lib-reflector, messages 17982-17984:

> Add additional entries in num_punct to cover the complex separator (French would be ';').

> Insert a space before the comma, which should eliminate the ambiguity.

> Solve the problem for ordered sequences in general, perhaps with a dedicated facet. Then complex should use that solution.

[ Bellevue: ]

> After much discussion, we agreed on the following: Add a footnote:

> [In a locale in which comma is being used as a decimal point character, inserting "showbase" into the output stream forces all outputs to show an explicit decimal point character; then all inserted complex sequences will extract unambiguously.]

> And move this to READY status.

[ Pre-Sophia Antipolis, Howard adds: ]

> Changed "showbase" to "showpoint" and changed from Ready to Review.

[ Post-Sophia Antipolis: ]

> I neglected to pull this issue from the formal motions page after the "showbase" to "showpoint" change. In Sophia Antipolis this change was reviewed by the LWG and the issue was set to Ready. We subsequently voted the footnote into the WP with "showbase".

> I'm changing from WP back to Ready to pick up the "showbase" to "showpoint" change.

Proposed resolution:

Add a footnote to 26.4.6 [complex.ops] p16:

> [In a locale in which comma is being used as a decimal point character, inserting `showpoint` into the output stream forces all outputs to show an explicit decimal point character; then all inserted complex sequences will extract unambiguously.]

### 630. arrays of valarray

Section: 26.6.2.1 [valarray.cons] Status: WP Submitter: Martin Sebor Opened: 2007-01-28 Last modified: 2009-10-26

View all other issues in [valarray.cons].

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Discussion:

Section 26.2 [numeric.requirements], p1 suggests that a `valarray` specialization on a type `T` that satisfies the requirements enumerated in the paragraph is itself a valid type on which `valarray` may be instantiated (Footnote 269 makes this clear). I.e., `valarray<valarray<T> >` is valid as long as `T` is valid. However, since implementations of `valarray` are permitted to initialize storage allocated by the class by invoking the default ctor of `T` followed by the copy assignment operator, such implementations of `valarray` wouldn't work with (perhaps user-defined) specializations of `valarray` whose assignment operator had undefined behavior when the size of its argument didn't match the size of `*this`. By "wouldn't work" I mean that it would be impossible to resize such an array of arrays by calling the `resize()` member function on it if the function used the copy assignment operator after constructing all elements using the default ctor (e.g., by invoking `new value_type[N]`) to obtain default-initialized storage) as it's permitted to do.

Stated more generally, the problem is that `valarray<valarray<T> >::resize(size_t)` isn't required or guaranteed to have well-defined semantics for every type `T` that satisfies all requirements in 26.2 [numeric.requirements].

I believe this problem was introduced by the adoption of the resolution outlined in N0857, Assignment of valarrays, from 1996. The copy assignment operator of the original numerical array classes proposed in N0280, as well as the one proposed in N0308 (both from 1993), had well-defined semantics for arrays of unequal size (the latter explicitly only when `*this` was empty; assignment of non empty arrays of unequal size was a runtime error).

The justification for the change given in N0857 was the "loss of performance [deemed] only significant for very simple operations on small arrays or for architectures with very few registers."

Since tiny arrays on a limited subset of hardware architectures are likely to be an exceedingly rare case (despite the continued popularity of x86) I propose to revert the resolution and make the behavior of all `valarray` assignment operators well-defined even for non-conformal arrays (i.e., arrays of unequal size). I have implemented this change and measured no significant degradation in performance in the common case (non-empty arrays of equal size). I have measured a 50% (and in some cases even greater) speedup in the case of assignments to empty arrays versus calling `resize()` first followed by an invocation of the copy assignment operator.

[ Bellevue: ]

> If no proposed wording by June meeting, this issue should be closed NAD.

[ 2009-07 Frankfurt ]

> Move resolution 1 to Ready.

> Howard: second resolution has been commented out (made invisible). Can be brought back on demand.

Proposed resolution:

Change 26.6.2.2 [valarray.assign], p1 as follows:

> `valarray<T>& operator=(const valarray<T>& x);`

> -1- Each element of the `*this` array is assigned the value of the corresponding element of the argument array. The resulting behavior is undefined if When the length of the argument array is not equal to the length of the *this array. resizes `*this` to make the two arrays the same length, as if by calling `resize(x.size())`, before performing the assignment.

And add a new paragraph just below paragraph 1 with the following text:

> -2- Postcondition: `size() == x.size()`.

Also add the following paragraph to 26.6.2.2 [valarray.assign], immediately after p4:

> -?- When the length, `N` of the array referred to by the argument is not equal to the length of `*this`, the operator resizes `*this` to make the two arrays the same length, as if by calling `resize(N)`, before performing the assignment.

[ pre-Sophia Antipolis, Martin adds the following compromise wording, but prefers the original proposed resolution: ]

[ Kona (2007): Gaby to propose wording for an alternative resolution in which you can assign to a `valarray` of size 0, but not to any other `valarray` whose size is unequal to the right hand side of the assignment. ]

### 634. `allocator.address()` doesn't work for types overloading `operator&`

Section: 20.8.8.1 [allocator.members] Status: CD1 Submitter: Howard Hinnant Opened: 2007-02-07 Last modified: 2008-09-26

View all other issues in [allocator.members].

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Duplicate of: 350

Discussion:

20.8.8.1 [allocator.members] says:

>     pointer address(reference x) const;

> > -1- Returns: `&x`.

20.8.8.1 [allocator.members] defines `CopyConstructible` which currently not only defines the semantics of copy construction, but also restricts what an overloaded `operator&` may do. I believe proposals are in the works (such as concepts and rvalue reference) to decouple these two requirements. Indeed it is not evident that we should disallow overloading `operator&` to return something other than the address of `*this`.

An example of when you want to overload `operator&` to return something other than the object's address is proxy references such as `vector<bool>` (or its replacement, currently code-named `bit_vector`). Taking the address of such a proxy reference should logically yield a proxy pointer, which when dereferenced, yields a copy of the original proxy reference again.

On the other hand, some code truly needs the address of an object, and not a proxy (typically for determining the identity of an object compared to a reference object). boost has long recognized this dilemma and solved it with `boost::addressof`. It appears to me that this would be useful functionality for the default allocator. Adopting this definition for `allocator::address` would free the standard of requiring anything special from types which overload `operator&`. Issue 580 is expected to make use of `allocator::address` mandatory for containers.

Proposed resolution:

Change 20.8.8.1 [allocator.members]:

>     pointer address(reference x) const;

> > -1- Returns: `&x`. The actual address of object referenced by x, even in the presence of an overloaded `operator&`.

>     const_pointer address(address(const_reference x) const;

> > -2- Returns: `&x`. The actual address of object referenced by x, even in the presence of an overloaded `operator&`.

[ post Oxford: This would be rendered NAD Editorial by acceptance of N2257. ]

[ Kona (2007): The LWG adopted the proposed resolution of N2387 for this issue which was subsequently split out into a separate paper N2436 for the purposes of voting. The resolution in N2436 addresses this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 638. deque end invalidation during erase

Section: 23.3.2.3 [deque.modifiers] Status: CD1 Submitter: Steve LoBasso Opened: 2007-02-17 Last modified: 2008-09-26

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Discussion:

The standard states at 23.3.2.3 [deque.modifiers]/4:

>     deque erase(...)

> Effects: ... An erase at either end of the deque invalidates only the iterators and the references to the erased elements.

This does not state that iterators to end will be invalidated. It needs to be amended in such a way as to account for end invalidation.

Something like:

> Any time the last element is erased, iterators to end are invalidated.

This would handle situations like:

>     erase(begin(), end())
>     erase(end() - 1)
>     pop_back()
>     resize(n, ...) where n < size()
>     pop_front() with size() == 1

[ Post Kona, Steve LoBasso notes: ]

> My only issue with the proposed resolution is that it might not be clear that `pop_front()` [where `size() == 1`] can invalidate past-the-end iterators.

Proposed resolution:

Change 23.3.2.3 [deque.modifiers], p4:

>     iterator erase(const_iterator position);
>     iterator erase(const_iterator first, const_iterator last);

> > -4- Effects: An erase in the middle of the `deque` invalidates all the iterators and references to elements of the `deque` and the past-the-end iterator. An erase at either end of the `deque` invalidates only the iterators and the references to the erased elements, except that erasing at the end also invalidates the past-the-end iterator.

[ Kona (2007): Proposed wording added and moved to Review. ]

[ Bellevue: ]

> Note that there is existing code that relies on iterators not being invalidated, but there are also existing implementations that do invalidate iterators. Thus, such code is not portable in any case. There is a pop_front() note, which should possibly be a separate issue. Mike Spertus to evaluate and, if need be, file an issue.

### 640. 27.6.2.5.2 does not handle (unsigned) long long

Section: 27.7.2.6.2 [ostream.inserters.arithmetic] Status: CD1 Submitter: Daniel Krügler Opened: 2007-02-17 Last modified: 2008-09-26

View all other issues in [ostream.inserters.arithmetic].

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Discussion:

The arithmetic inserters are described in 27.7.2.6.2 [ostream.inserters.arithmetic]. Although the section starts with a listing of the inserters including the new ones:

>     operator<<(long long val );
>     operator<<(unsigned long long val );

the text in paragraph 1, which describes the corresponding effects of the inserters, depending on the actual type of val, does not handle the types `long long` and `unsigned long long`.

[ Alisdair: In addition to the (unsigned) long long problem, that whole paragraph misses any reference to extended integral types supplied by the implementation - one of the additions by core a couple of working papers back. ]

Proposed resolution:

In 27.7.2.6.2 [ostream.inserters.arithmetic]/1 change the third sentence

> When val is of type `bool`, `long`, `unsigned long`, long long, unsigned long long, `double`, `long double`, or `const void*`, the formatting conversion occurs as if it performed the following code fragment:

### 643. Impossible "as if" clauses

Section: 27.9.1.1 [filebuf], 22.4.2.2.2 [facet.num.put.virtuals] Status: CD1 Submitter: Daniel Krügler Opened: 2007-02-20 Last modified: 2008-09-26

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Discussion:

The current standard 14882:2003(E) as well as N2134 have the following defects:

27.9.1.1 [filebuf]/5 says:

> In order to support file I/O and multibyte/wide character conversion, conversions are performed using members of a facet, referred to as `a_codecvt` in following sections, obtained "as if" by

> >     codecvt<charT,char,typename traits::state_type> a_codecvt =
> >       use_facet<codecvt<charT,char,typename traits::state_type> >(getloc());

`use_facet` returns a `const facet` reference and no facet is copyconstructible, so the codecvt construction should fail to compile.

A similar issue arises in 22.4.2.2.2 [facet.num.put.virtuals]/15 for `num_punct`.

Proposed resolution:

In 27.9.1.1 [filebuf]/5 change the "as if" code

>     const codecvt<charT,char,typename traits::state_type>& a_codecvt =
>       use_facet<codecvt<charT,char,typename traits::state_type> >(getloc());

In 22.4.2.2.2 [facet.num.put.virtuals]/15 (This is para 5 in N2134) change

> A local variable `punct` is initialized via

> >     const numpunct<charT>& punct = use_facet< numpunct<charT> >(str.getloc() );

(Please note also the additional provided trailing semicolon)

### 646. const incorrect match_result members

Section: 28.10.4 [re.results.form] Status: CD1 Submitter: Daniel Krügler Opened: 2007-02-26 Last modified: 2008-09-26

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Discussion:

28.10.4 [re.results.form] (root and para 3) in N2134 defines the two function template members format as non-const functions, although they are declared as const in 28.10 [re.results]/3.

Proposed resolution:

Add the missing `const` specifier to both `format` overloads described in section 28.10.4 [re.results.form].

### 650. regex_token_iterator and const correctness

Section: 28.12.2 [re.tokiter] Status: CD1 Submitter: Daniel Krügler Opened: 2007-03-05 Last modified: 2008-09-26

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Discussion:

Both the class definition of regex_token_iterator (28.12.2 [re.tokiter]/6) and the latter member specifications (28.12.2.2 [re.tokiter.comp]/1+2) declare both comparison operators as non-const functions. Furtheron, both dereference operators are unexpectedly also declared as non-const in 28.12.2 [re.tokiter]/6 as well as in (28.12.2.3 [re.tokiter.deref]/1+2).

Proposed resolution:

1) In (28.12.2 [re.tokiter]/6) change the current declarations

>     bool operator==(const regex_token_iterator&) const;
>     bool operator!=(const regex_token_iterator&) const;
>     const value_type& operator*() const;
>     const value_type* operator->() const;

2) In 28.12.2.2 [re.tokiter.comp] change the following declarations

>     bool operator==(const regex_token_iterator& right) const;
>     bool operator!=(const regex_token_iterator& right) const;

3) In 28.12.2.3 [re.tokiter.deref] change the following declarations

>     const value_type& operator*() const;
>     const value_type* operator->() const;

[ Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue (which is to adopt the proposed wording in this issue). The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 651. Missing preconditions for regex_token_iterator c'tors

Section: 28.12.2.1 [re.tokiter.cnstr] Status: CD1 Submitter: Daniel Krügler Opened: 2007-03-05 Last modified: 2008-09-26

View all other issues in [re.tokiter.cnstr].

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Discussion:

The text provided in 28.12.2.1 [re.tokiter.cnstr]/2+3 describes the effects of the three non-default constructors of class template regex_token_iterator but is does not clarify which values are legal values for submatch/submatches. This becomes an issue, if one takes 28.12.2 [re.tokiter]/9 into account, which explains the notion of a "current match" by saying:

> The current match is `(*position).prefix()` if `subs[N] == -1`, or `(*position)[subs[N]]` for any other value of `subs[N]`.

It's not clear to me, whether other negative values except -1 are legal arguments or not - it seems they are not.

Proposed resolution:

Add the following precondition paragraph just before the current 28.12.2.1 [re.tokiter.cnstr]/2:

> Requires: Each of the initialization values of `subs` must be `>= -1`.

[ Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue (which is to adopt the proposed wording in this issue). The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 652. regex_iterator and const correctness

Section: 28.12.1 [re.regiter] Status: CD1 Submitter: Daniel Krügler Opened: 2007-03-05 Last modified: 2008-09-26

View all issues with CD1 status.

Discussion:

Both the class definition of regex_iterator (28.12.1 [re.regiter]/1) and the latter member specification (28.12.1.2 [re.regiter.comp]/1+2) declare both comparison operators as non-const functions. Furtheron, both dereference operators are unexpectedly also declared as non-const in 28.12.1 [re.regiter]/1 as well as in (28.12.1.3 [re.regiter.deref]/1+2).

Proposed resolution:

1) In (28.12.1 [re.regiter]/1) change the current declarations

>     bool operator==(const regex_iterator&) const;
>     bool operator!=(const regex_iterator&) const;
>     const value_type& operator*() const;
>     const value_type* operator->() const;

2) In 28.12.1.3 [re.regiter.deref] change the following declarations

>     const value_type& operator*() const;
>     const value_type* operator->() const;

3) In 28.12.1.2 [re.regiter.comp] change the following declarations

>     bool operator==(const regex_iterator& right) const;
>     bool operator!=(const regex_iterator& right) const;

[ Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue (which is to adopt the proposed wording in this issue). The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 654. Missing IO roundtrip for random number engines

Section: X [rand.req.eng] Status: CD1 Submitter: Daniel Krügler Opened: 2007-03-08 Last modified: 2009-05-01

View all other issues in [rand.req.eng].

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Discussion:

Table 98 and para 5 in X [rand.req.eng] specify the IO insertion and extraction semantic of random number engines. It can be shown, v.i., that the specification of the extractor cannot guarantee to fulfill the requirement from para 5:

> If a textual representation written via os << x was subsequently read via is >> v, then x == v provided that there have been no intervening invocations of x or of v.

The problem is, that the extraction process described in table 98 misses to specify that it will initially set the if.fmtflags to ios_base::dec, see table 104:

> dec: converts integer input or generates integer output in decimal base

Proof: The following small program demonstrates the violation of requirements (exception safety not fulfilled):

>     #include <cassert>
>     #include <ostream>
>     #include <iostream>
>     #include <iomanip>
>     #include <sstream>

>     class RanNumEngine {
>       int state;
>     public:
>       RanNumEngine() : state(42) {}

>       bool operator==(RanNumEngine other) const {
>           return state == other.state;
>       }

>       template <typename Ch, typename Tr>
>       friend std::basic_ostream<Ch, Tr>& operator<<(std::basic_ostream<Ch, Tr>& os, RanNumEngine engine) {
>         Ch old = os.fill(os.widen(' ')); // Sets space character
>         std::ios_base::fmtflags f = os.flags();
>         os << std::dec << std::left << engine.state; // Adds ios_base::dec|ios_base::left
>         os.fill(old); // Undo
>         os.flags(f);
>         return os;
>       }

>       template <typename Ch, typename Tr>
>       friend std::basic_istream<Ch, Tr>& operator>>(std::basic_istream<Ch, Tr>& is, RanNumEngine& engine) {
>            // Uncomment only for the fix.

>         //std::ios_base::fmtflags f = is.flags();
>         //is >> std::dec;
>         is >> engine.state;
>         //is.flags(f);
>         return is;
>       }
>     };

>     int main() {
>         std::stringstream s;
>         s << std::setfill('#'); // No problem
>             s << std::oct; // Yikes!
>             // Here starts para 5 requirements:
>         RanNumEngine x;
>         s << x;
>         RanNumEngine v;
>         s >> v;
>         assert(x == v); // Fails: 42 == 34
>     }

A second, minor issue seems to be, that the insertion description from table 98 unnecessarily requires the addition of ios_base::fixed (which only influences floating-point numbers). Its not entirely clear to me whether the proposed standard does require that the state of random number engines is stored in integral types or not, but I have the impression that this is the indent, see e.g. p. 3

> The specification of each random number engine defines the size of its state in multiples of the size of its result_type.

If other types than integrals are supported, then I wonder why no requirements are specified for the precision of the stream.

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 655. Signature of generate_canonical not useful

Section: 26.5.7.2 [rand.util.canonical] Status: CD1 Submitter: Daniel Krügler Opened: 2007-03-08 Last modified: 2008-09-26

View all other issues in [rand.util.canonical].

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Discussion:

In 26.5.1 [rand.synopsis] we have the declaration

>     template<class RealType, class UniformRandomNumberGenerator,
>       size_t bits>
>     result_type generate_canonical(UniformRandomNumberGenerator& g);

Besides the "result_type" issue (already recognized by Bo Persson at Sun, 11 Feb 2007 05:26:47 GMT in this group) it's clear, that the template parameter order is not reasonably choosen: Obviously one always needs to specify all three parameters, although usually only two are required, namely the result type RealType and the wanted bits, because UniformRandomNumberGenerator can usually be deduced.

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 659. istreambuf_iterator should have an operator->()

Section: 24.6.3 [istreambuf.iterator] Status: WP Submitter: Niels Dekker Opened: 2007-03-25 Last modified: 2009-10-26

View all other issues in [istreambuf.iterator].

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Discussion:

Greg Herlihy has clearly demonstrated that a user defined input iterator should have an operator->(), even if its value type is a built-in type (comp.std.c++, "Re: Should any iterator have an operator->() in C++0x?", March 2007). And as Howard Hinnant remarked in the same thread that the input iterator `istreambuf_iterator` doesn't have one, this must be a defect!

Based on Greg's example, the following code demonstrates the issue:

     #include <iostream>
     #include <fstream>
     #include <streambuf>

     typedef char C;
     int main ()
     {
       std::ifstream s("filename", std::ios::in);
       std::istreambuf_iterator<char> i(s);

       (*i).~C();  // This is well-formed...
       i->~C();  // ... so this should be supported!
     }

Of course, operator-> is also needed when the value_type of istreambuf_iterator is a class.

The operator-> could be implemented in various ways. For instance, by storing the current value inside the iterator, and returning its address. Or by returning a proxy, like operator_arrow_proxy, from http://www.boost.org/boost/iterator/iterator_facade.hpp

I hope that the resolution of this issue will contribute to getting a clear and consistent definition of iterator concepts.

[ Kona (2007): The proposed resolution is inconsistent because the return type of `istreambuf_iterator::operator->()` is specified to be `pointer`, but the proposed text also states that "`operator->` may return a proxy." ]

[ Niels Dekker (mailed to Howard Hinnant): ]

> The proposed resolution does not seem inconsistent to me. `istreambuf_iterator::operator->()` should have `istreambuf_iterator::pointer` as return type, and this return type may in fact be a proxy.

> AFAIK, the resolution of 445 ("`iterator_traits::reference` unspecified for some iterator categories") implies that for any iterator class `Iter`, the return type of `operator->()` is `Iter::pointer`, by definition. I don't think `Iter::pointer` needs to be a raw pointer.

> Still I wouldn't mind if the text "`operator->` may return a proxy" would be removed from the resolution. I think it's up to the library implementation, how to implement `istreambuf_iterator::operator->()`. As longs as it behaves as expected: `i->m` should have the same effect as `(*i).m`. Even for an explicit destructor call, `i->~C()`. The main issue is just: `istreambuf_iterator` should have an `operator->()`!

[ 2009-04-30 Alisdair adds: ]

> Note that operator-> is now a requirement in the `InputIterator` concept, so this issue cannot be ignored or existing valid programs will break when compiled with an 0x library.

[ 2009-05-29 Alisdair adds: ]

> I agree with the observation that in principle the type 'pointer' may be a proxy, and the words highlighting this are redundant.

> However, in the current draught `pointer` is required to be exactly '`charT *`' by the derivation from `std::iterator`. At a minimum, the 4th parameter of this base class template should become unspecified. That permits the introduction of a proxy as a nested class in some further undocumented (not even exposition-only) base.

> It also permits the `istream_iterator` approach where the cached value is stored in the iterator itself, and the iterator serves as its own proxy for post-increment `operator++` - removing the need for the existing exposition-only nested class `proxy`.

> Note that the current `proxy` class also has exactly the right properties to serve as the pointer `proxy` too. This is likely to be a common case where an `InputIterator` does not hold internal state but delegates to another class.

> Proposed Resolution:

> In addition to the current proposal:

> 24.6.3 [istreambuf.iterator]

> >     template<class charT, class traits = char_traits<charT> >
> >     class istreambuf_iterator
> >       : public iterator<input_iterator_tag, charT,
> >                         typename traits::off_type, charT* unspecified, charT> {

[ 2009-07 Frankfurt ]

> Move the additional part into the proposed resolution, and wrap the descriptive text in a Note.

> [Howard: done.]

> Move to Ready.

Proposed resolution:

Add to the synopsis in 24.6.3 [istreambuf.iterator]:

>     charT operator*() const;
>     pointer operator->() const;
>     istreambuf_iterator<charT,traits>& operator++();

24.6.3 [istreambuf.iterator]

>     template<class charT, class traits = char_traits<charT> >
>     class istreambuf_iterator
>       : public iterator<input_iterator_tag, charT,
>                         typename traits::off_type, charT* unspecified, charT> {

Change 24.6.3 [istreambuf.iterator], p1:

> The class template `istreambuf_iterator` reads successive characters from the `streambuf` for which it was constructed. `operator*` provides access to the current input character, if any. [Note: `operator->` may return a proxy. — end note] Each time `operator++` is evaluated, the iterator advances to the next input character. If the end of stream is reached (`streambuf_type::sgetc()` returns `traits::eof()`), the iterator becomes equal to the end of stream iterator value. The default constructor `istreambuf_iterator()` and the constructor `istreambuf_iterator(0)` both construct an end of stream iterator object suitable for use as an end-of-range.

### 660. Missing Bitwise Operations

Section: 20.7 [function.objects] Status: CD1 Submitter: Beman Dawes Opened: 2007-04-02 Last modified: 2008-09-26

View all other issues in [function.objects].

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Discussion:

Section 20.7 [function.objects] provides function objects for some unary and binary operations, but others are missing. In a LWG reflector discussion, beginning with c++std-lib-18078, pros and cons of adding some of the missing operations were discussed. Bjarne Stroustrup commented "Why standardize what isn't used? Yes, I see the chicken and egg problems here, but it would be nice to see a couple of genuine uses before making additions."

A number of libraries, including Rogue Wave, GNU, Adobe ASL, and Boost, have already added these functions, either publicly or for internal use. For example, Doug Gregor commented: "Boost will also add ... (|, &, ^) in 1.35.0, because we need those function objects to represent various parallel collective operations (reductions, prefix reductions, etc.) in the new Message Passing Interface (MPI) library."

Because the bitwise operators have the strongest use cases, the proposed resolution is limited to them.

Proposed resolution:

To 20.7 [function.objects], Function objects, paragraph 2, add to the header <functional> synopsis:

>     template <class T> struct bit_and;
>     template <class T> struct bit_or;
>     template <class T> struct bit_xor;

At a location in clause 20 to be determined by the Project Editor, add:

> The library provides basic function object classes for all of the bitwise operators in the language ([expr.bit.and], [expr.or], [exp.xor]).

>     template <class T> struct bit_and : binary_function<T,T,T> {
>       T operator()(const T& x , const T& y ) const;
>     };

> > `operator()` returns`x & y` .

>     template <class T> struct bit_or : binary_function<T,T,T> {
>       T operator()(const T& x , const T& y ) const;
>     };

> > `operator()` returns `x | y` .

>     template <class T> struct bit_xor : binary_function<T,T,T> {
>       T operator()(const T& x , const T& y ) const;
>     };

> > `operator()` returns `x ^ y` .

### 661. New 27.6.1.2.2 changes make special extractions useless

Section: 27.7.1.2.2 [istream.formatted.arithmetic] Status: CD1 Submitter: Daniel Krügler Opened: 2007-04-01 Last modified: 2008-09-26

View all other issues in [istream.formatted.arithmetic].

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Discussion:

To the more drastic changes of 27.7.1.2.2 [istream.formatted.arithmetic] in the current draft N2134 belong the explicit description of the extraction of the types short and int in terms of as-if code fragments.

1. The corresponding as-if extractions in paragraph 2 and 3 will never result in a change of the operator>> argument val, because the contents of the local variable lval is in no case written into val. Furtheron both fragments need a currently missing parentheses in the beginning of the if-statement to be valid C++.
2. I would like to ask whether the omission of a similar explicit extraction of unsigned short and unsigned int in terms of long - compared to their corresponding new insertions, as described in 27.7.2.6.2 [ostream.inserters.arithmetic], is a deliberate decision or an oversight.

Proposed resolution:

1. In 27.7.1.2.2 [istream.formatted.arithmetic]/2 change the current as-if code fragment

   >     typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
   >     iostate err = 0;
   >     long lval;
   >     use_facet<numget>(loc).get(*this, 0, *this, err, lval );
   >     if (err == 0) {
   >       && if (lval < numeric_limits<short>::min() || numeric_limits<short>::max() < lval))
   >           err = ios_base::failbit;
   >       else
   >         val = static_cast<short>(lval);
   >     }
   >     setstate(err);

   Similarily in 27.7.1.2.2 [istream.formatted.arithmetic]/3 change the current as-if fragment

   >     typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
   >     iostate err = 0;
   >     long lval;
   >     use_facet<numget>(loc).get(*this, 0, *this, err, lval );
   >     if (err == 0) {
   >       && if (lval < numeric_limits<int>::min() || numeric_limits<int>::max() < lval))
   >           err = ios_base::failbit;
   >       else
   >         val = static_cast<int>(lval);
   >     }
   >     setstate(err);

2. ---

[ Kona (2007): Note to the editor: the name lval in the call to `use_facet` is incorrectly italicized in the code fragments corresponding to `operator>>(short &)` and `operator >>(int &)`. Also, val -- which appears twice on the line with the `static_cast` in the proposed resolution -- should be italicized. Also, in response to part two of the issue: this is deliberate. ]

### 664. `do_unshift` for `codecvt<char, char, mbstate_t>`

Section: 22.4.1.4.2 [locale.codecvt.virtuals] Status: CD1 Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2008-09-26

View all other issues in [locale.codecvt.virtuals].

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Discussion:

22.4.1.4.2 [locale.codecvt.virtuals], para 7 says (regarding `do_unshift`):

> Effects: Places characters starting at to that should be appended to terminate a sequence when the current `stateT` is given by `state`.237) Stores no more than `(to_limit - to)` destination elements, and leaves the `to_next` pointer pointing one beyond the last element successfully stored. `codecvt<char, char, mbstate_t>` stores no characters.

The following objection has been raised:

> Since the C++ Standard permits a nontrivial conversion for the required instantiations of `codecvt`, it is overly restrictive to say that `do_unshift` must store no characters and return `noconv`.

[Plum ref _222152Y50]

Proposed resolution:

Change 22.4.1.4.2 [locale.codecvt.virtuals], p7:

> Effects: Places characters starting at to that should be appended to terminate a sequence when the current `stateT` is given by state.237) Stores no more than (to_limit -to) destination elements, and leaves the to_next pointer pointing one beyond the last element successfully stored. `codecvt<char, char, mbstate_t>` stores no characters.

### 665. `do_unshift` return value

Section: 22.4.1.4.2 [locale.codecvt.virtuals] Status: CD1 Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2008-09-26

View all other issues in [locale.codecvt.virtuals].

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Discussion:

22.4.1.4.2 [locale.codecvt.virtuals], para 8 says:

> `codecvt<char,char,mbstate_t>`, returns `noconv`.

The following objection has been raised:

> Despite what the C++ Standard says, `unshift` can't always return `noconv` for the default facets, since they can be nontrivial. At least one implementation does whatever the C functions do.

[Plum ref _222152Y62]

Proposed resolution:

Change 22.4.1.4.2 [locale.codecvt.virtuals], p8:

> Returns: An enumeration value, as summarized in Table 76:

> ...

> `codecvt<char,char,mbstate_t>`, returns `noconv`.

### 666. `moneypunct::do_curr_symbol()`

Section: 22.4.6.3.2 [locale.moneypunct.virtuals] Status: CD1 Submitter: Thomas Plum Opened: 2007-04-16 Last modified: 2008-09-26

View all other issues in [locale.moneypunct.virtuals].

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Discussion:

22.4.6.3.2 [locale.moneypunct.virtuals], para 4 footnote 257 says

> 257) For international specializations (second template parameter `true`) this is always four characters long, usually three letters and a space.

The following objection has been raised:

> The international currency symbol is whatever the underlying locale says it is, not necessarily four characters long.

[Plum ref _222632Y41]

Proposed resolution:

Change footnote 253 in 22.4.6.3.2 [locale.moneypunct.virtuals]:

> 253) For international specializations (second template parameter `true`) this is always typically four characters long, usually three letters and a space.

### 672. Swappable requirements need updating

Section: 20.2.1 [utility.arg.requirements] Status: CD1 Submitter: Howard Hinnant Opened: 2007-05-04 Last modified: 2008-09-26

View other active issues in [utility.arg.requirements].

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Discussion:

The current `Swappable` is:

> Table 37: `Swappable` requirements [swappable]
> expression | return type | post-condition
> --- | --- | ---
> `swap(s,t)` | `void` | `t` has the value originally held by `u`, and `u` has the value originally held by `t`
> The Swappable requirement is met by satisfying one or more of the following conditions: `T` is Swappable if `T` satisfies the `CopyConstructible` requirements (Table 34) and the `CopyAssignable` requirements (Table 36); `T` is Swappable if a namespace scope function named `swap` exists in the same namespace as the definition of `T`, such that the expression `swap(t,u)` is valid and has the semantics described in this table.

With the passage of rvalue reference into the language, `Swappable` needs to be updated to require only `MoveConstructible` and `MoveAssignable`. This is a minimum.

Additionally we may want to support proxy references such that the following code is acceptable:

>     namespace Mine {

>     template <class T>
>     struct proxy {...};

>     template <class T>
>     struct proxied_iterator
>     {
>        typedef T value_type;
>        typedef proxy<T> reference;
>        reference operator*() const;
>        ...
>     };

>     struct A
>     {
>        // heavy type, has an optimized swap, maybe isn't even copyable or movable, just swappable
>        void swap(A&);
>        ...
>     };

>     void swap(A&, A&);
>     void swap(proxy<A>, A&);
>     void swap(A&, proxy<A>);
>     void swap(proxy<A>, proxy<A>);

>     }  // Mine

>     ...

>     Mine::proxied_iterator<Mine::A> i(...)
>     Mine::A a;
>     swap(*i1, a);

I.e. here is a call to `swap` which the user enables swapping between a proxy to a class and the class itself. We do not need to anything in terms of implementation except not block their way with overly constrained concepts. That is, the `Swappable` concept should be expanded to allow swapping between two different types for the case that one is binding to a user-defined `swap`.

Proposed resolution:

Change 20.2.1 [utility.arg.requirements]:

> -1- The template definitions in the C++ Standard Library refer to various named requirements whose details are set out in tables 31-38. In these tables, `T` is a type to be supplied by a C++ program instantiating a template; `a`, `b`, and `c` are values of type `const T`; `s` and `t` are modifiable lvalues of type `T`; `u` is a value of type (possibly `const`) `T`; and `rv` is a non-`const` rvalue of type `T`.

> Table 37: `Swappable` requirements [swappable]
> expression | return type | post-condition
> --- | --- | ---
> `swap(s,t)` | `void` | `t` has the value originally held by `u`, and `u` has the value originally held by `t`
> The `Swappable` requirement is met by satisfying one or more of the following conditions: `T` is `Swappable` if `T` satisfies the `CopyConstructible` MoveConstructible requirements (Table 34 33) and the `CopyAssignable` MoveAssignable requirements (Table 36 35); `T` is `Swappable` if a namespace scope function named `swap` exists in the same namespace as the definition of `T`, such that the expression `swap(t,u)` is valid and has the semantics described in this table.

[ Kona (2007): We like the change to the `Swappable` requirements to use move semantics. The issue relating to the support of proxies is separable from the one relating to move semantics, and it's bigger than just swap. We'd like to address only the move semantics changes under this issue, and open a separated issue (742) to handle proxies. Also, there may be a third issue, in that the current definition of `Swappable` does not permit rvalues to be operands to a swap operation, and Howard's proposed resolution would allow the right-most operand to be an rvalue, but it would not allow the left-most operand to be an rvalue (some swap functions in the library have been overloaded to permit left operands to swap to be rvalues). ]

### 673. `unique_ptr` update

Section: 20.8.14 [unique.ptr] Status: CD1 Submitter: Howard Hinnant Opened: 2007-05-04 Last modified: 2008-09-26

View all other issues in [unique.ptr].

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Discussion:

Since the publication of N1856 there have been a few small but significant advances which should be included into `unique_ptr`. There exists a example implmenation for all of these changes.

- Even though `unique_ptr<void>` is not a valid use case (unlike for `shared_ptr<void>`), unexpected cases to crop up which require the instantiation of the interface of `unique_ptr<void>` even if it is never used. For example see LWG 541 for how this accidently happened to `auto_ptr`. I believe the most robust way to protect `unique_ptr` against this type of failure is to augment the return type of `unique_ptr<T>:operator*()` with `add_lvalue_reference<T>::type`. This means that given an instantiated `unique_ptr<void>` the act of dereferencing it will simply return `void` instead of causing a compile time failure. This is simpler than creating a `unique_ptr<void>` specialization which isn't robust in the face of `cv-`qualified `void` types.

  This resolution also supports instantiations such as `unique_ptr<void, free_deleter>` which could be very useful to the client.

- Efforts have been made to better support containers and smart pointers in shared memory contexts. One of the key hurdles in such support is not assuming that a pointer type is actually a `T*`. This can easily be accomplished for `unique_ptr` by having the deleter define the pointer type: `D::pointer`. Furthermore this type can easily be defaulted to `T*` should the deleter `D` choose not to define a pointer type (example implementation here). This change has no run time overhead. It has no interface overhead on authors of custom delter types. It simply allows (but not requires) authors of custom deleter types to define a smart pointer for the storage type of `unique_ptr` if they find such functionality useful. `std::default_delete` is an example of a deleter which defaults `pointer` to `T*` by simply ignoring this issue and not including a `pointer typedef`.

- When the deleter type is a function pointer then it is unsafe to construct a `unique_ptr` without specifying the function pointer in the constructor. This case is easy to check for with a `static_assert` assuring that the deleter is not a pointer type in those constructors which do not accept deleters.

  >     unique_ptr<A, void(*)(void*)> p(new A);  // error, no function given to delete the pointer!

[ Kona (2007): We don't like the solution given to the first bullet in light of concepts. The second bullet solves the problem of supporting fancy pointers for one library component only. The full LWG needs to decide whether to solve the problem of supporting fancy pointers piecemeal, or whether a paper addressing the whole library is needed. We think that the third bullet is correct. ]

[ Post Kona: Howard adds example user code related to the first bullet: ]

>     void legacy_code(void*, std::size_t);

>     void foo(std::size_t N)
>     {
>         std::unique_ptr<void, void(*)(void*)> ptr(std::malloc(N), std::free);
>         legacy_code(ptr.get(), N);
>     }   // unique_ptr used for exception safety purposes

I.e. `unique_ptr<void>` is a useful tool that we don't want to disable with concepts. The only part of `unique_ptr<void>` we want to disable (with concepts or by other means) are the two member functions:

>     T& operator*() const;
>     T* operator->() const;

Proposed resolution:

[ I am grateful for the generous aid of Peter Dimov and Ion Gaztañaga in helping formulate and review the proposed resolutions below. ]

- Change 20.8.14.2 [unique.ptr.single]:

  >     template <class T, class D = default_delete<T>> class unique_ptr {
  >        ...
  >        T& typename add_lvalue_reference<T>::type operator*() const;
  >        ...
  >     };

  Change 20.8.14.2.4 [unique.ptr.single.observers]:

  >     T& typename add_lvalue_reference<T>::type operator*() const;

- Change 20.8.14.2 [unique.ptr.single]:

  >     template <class T, class D = default_delete<T>> class unique_ptr {
  >     public:
  >       typedef implementation (see description below) pointer;
  >        ...
  >        explicit unique_ptr(T* pointer p);
  >        ...
  >        unique_ptr(T* pointer p, implementation defined (see description below) d);
  >        unique_ptr(T* pointer p, implementation defined (see description below) d);
  >        ...
  >        T* pointer operator->() const;
  >        T* pointer get() const;
  >        ...
  >        T* pointer release();
  >        void reset(T* pointer p = 0 pointer());
  >     };

  -3- If the type `remove_reference<D>::type::pointer` exists, then `unique_ptr<T, D>::pointer` is a typedef to `remove_reference<D>::type::pointer`. Otherwise `unique_ptr<T, D>::pointer` is a typedef to `T*`. The type `unique_ptr<T, D>::pointer` shall be `CopyConstructible` and `CopyAssignable`.

  Change 20.8.14.2.1 [unique.ptr.single.ctor]:

  >     unique_ptr(T* pointer p);
  >     ...
  >     unique_ptr(T* pointer p, implementation defined d);
  >     unique_ptr(T* pointer p, implementation defined d);
  >     ...
  >     unique_ptr(T* pointer p, const A& d);
  >     unique_ptr(T* pointer p, A&& d);
  >     ...
  >     unique_ptr(T* pointer p, A& d);
  >     unique_ptr(T* pointer p, A&& d);
  >     ...
  >     unique_ptr(T* pointer p, const A& d);
  >     unique_ptr(T* pointer p, const A&& d);
  >     ...

  -23- Requires: If `D` is not a reference type, construction of the deleter `D` from an rvalue of type `E` must shall be well formed and not throw an exception. If `D` is a reference type, then `E` must shall be the same type as `D` (diagnostic required). `U*` `unique_ptr<U,E>::pointer` must shall be implicitly convertible to `T*` pointer.

  -25- Postconditions: `get() == value u.get()` had before the construction, modulo any required offset adjustments resulting from the cast from `U*` `unique_ptr<U,E>::pointer` to `T*` pointer. `get_deleter()` returns a reference to the internally stored deleter which was constructed from `u.get_deleter()`.

  Change 20.8.14.2.3 [unique.ptr.single.asgn]:

  > -8- Requires: Assignment of the deleter `D` from an rvalue `D` must shall not throw an exception. `U*` `unique_ptr<U,E>::pointer` must shall be implicitly convertible to `T*` pointer.

  Change 20.8.14.2.4 [unique.ptr.single.observers]:

  >     T* pointer operator->() const;

  > ...

  >     T* pointer get() const;

  Change 20.8.14.2.5 [unique.ptr.single.modifiers]:

  >     T* pointer release();

  > ...

  >     void reset(T* pointer p = 0 pointer());

  Change 20.8.14.3 [unique.ptr.runtime]:

  >     template <class T, class D> class unique_ptr<T[], D> {
  >     public:
  >       typedef implementation pointer;
  >        ...
  >        explicit unique_ptr(T* pointer p);
  >        ...
  >        unique_ptr(T* pointer p, implementation defined d);
  >        unique_ptr(T* pointer p, implementation defined d);
  >        ...
  >        T* pointer get() const;
  >        ...
  >        T* pointer release();
  >        void reset(T* pointer p = 0 pointer());
  >     };

  Change 20.8.14.3.1 [unique.ptr.runtime.ctor]:

  >     unique_ptr(T* pointer p);
  >     unique_ptr(T* pointer p, implementation defined d);
  >     unique_ptr(T* pointer p, implementation defined d);

  > These constructors behave the same as in the primary template except that they do not accept pointer types which are convertible to `T*` `pointer`. [Note: One implementation technique is to create private templated overloads of these members. -- end note]

  Change 20.8.14.3.3 [unique.ptr.runtime.modifiers]:

  >     void reset(T* pointer p = 0 pointer());

  > -1- Requires: Does not accept pointer types which are convertible to `T*` `pointer` (diagnostic required). [Note: One implementation technique is to create a private templated overload. -- end note]

- Change 20.8.14.2.1 [unique.ptr.single.ctor]:

  >     unique_ptr();

  > > Requires: `D` must shall be default constructible, and that construction must shall not throw an exception. `D` must shall not be a reference type or pointer type (diagnostic required).

  >     unique_ptr(T* pointer p);

  > > Requires: The expression `D()(p)` must shall be well formed. The default constructor of `D` must shall not throw an exception. `D` must shall not be a reference type or pointer type (diagnostic required).

### 674. `shared_ptr` interface changes for consistency with N1856

Section: 20.8.15.2 [util.smartptr.shared] Status: CD1 Submitter: Peter Dimov Opened: 2007-05-05 Last modified: 2008-09-26

View all other issues in [util.smartptr.shared].

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Discussion:

N1856 does not propose any changes to `shared_ptr`. It needs to be updated to use a rvalue reference where appropriate and to interoperate with `unique_ptr` as it does with `auto_ptr`.

Proposed resolution:

Change 20.8.15.2 [util.smartptr.shared] as follows:

>     template<class Y> explicit shared_ptr(auto_ptr<Y>&&& r);
>     template<class Y, class D> explicit shared_ptr(const unique_ptr<Y,D>& r) = delete;
>     template<class Y, class D> explicit shared_ptr(unique_ptr<Y,D>&& r);
>     ...
>     template<class Y> shared_ptr& operator=(auto_ptr<Y>&&& r);
>     template<class Y, class D> shared_ptr& operator=(const unique_ptr<Y,D>& r) = delete;
>     template<class Y, class D> shared_ptr& operator=(unique_ptr<Y,D>&& r);

Change 20.8.15.2.1 [util.smartptr.shared.const] as follows:

>     template<class Y> shared_ptr(auto_ptr<Y>&&& r);

Add to 20.8.15.2.1 [util.smartptr.shared.const]:

>     template<class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);

> > Effects: Equivalent to `shared_ptr( r.release(), r.get_deleter() )` when `D` is not a reference type, `shared_ptr( r.release(), ref( r.get_deleter() ) )` otherwise.

> > Exception safety: If an exception is thrown, the constructor has no effect.

Change 20.8.15.2.3 [util.smartptr.shared.assign] as follows:

>     template<class Y> shared_ptr& operator=(auto_ptr<Y>&&& r);

Add to 20.8.15.2.3 [util.smartptr.shared.assign]:

>     template<class Y, class D> shared_ptr& operator=(unique_ptr<Y,D>&& r);

> > -4- Effects: Equivalent to `shared_ptr(std::move(r)).swap(*this)`.

> > -5- Returns: `*this`.

[ Kona (2007): We may need to open an issue (743) to deal with the question of whether `shared_ptr` needs an rvalue `swap`. ]

### 675. Move assignment of containers

Section: 23.2 [container.requirements] Status: CD1 Submitter: Howard Hinnant Opened: 2007-05-05 Last modified: 2008-09-26

View other active issues in [container.requirements].

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Discussion:

James Hopkin pointed out to me that if `vector<T>` move assignment is O(1) (just a `swap`) then containers such as `vector<shared_ptr<ostream>>` might have the wrong semantics under move assignment when the source is not truly an rvalue, but a moved-from lvalue (destructors could run late).

>     vector<shared_ptr<ostream>> v1;
>     vector<shared_ptr<ostream>> v2;
>     ...
>     v1 = v2;               // #1
>     v1 = std::move(v2);    // #2

Move semantics means not caring what happens to the source (`v2` in this example). It doesn't mean not caring what happens to the target (`v1`). In the above example both assignments should have the same effect on `v1`. Any non-shared `ostream`'s `v1` owns before the assignment should be closed, whether `v1` is undergoing copy assignment or move assignment.

This implies that the semantics of move assignment of a generic container should be `clear, swap` instead of just swap. An alternative which could achieve the same effect would be to move assign each element. In either case, the complexity of move assignment needs to be relaxed to `O(v1.size())`.

The performance hit of this change is not nearly as drastic as it sounds. In practice, the target of a move assignment has always just been move constructed or move assigned from. Therefore under `clear, swap` semantics (in this common use case) we are still achieving O(1) complexity.

Proposed resolution:

Change 23.2 [container.requirements]:

> Table 89: Container requirements
> expression | return type | operational semantics | assertion/note pre/post-condition | complexity
> --- | --- | --- | --- | ---
> `a = rv;` | `X&` | All existing elements of `a` are either move assigned or destructed | `a` shall be equal to the value that `rv` had before this construction | (Note C) linear

> Notes: the algorithms `swap()`, `equal()` and `lexicographical_compare()` are defined in clause 25. Those entries marked "(Note A)" should have constant complexity. Those entries marked "(Note B)" have constant complexity unless `allocator_propagate_never<X::allocator_type>::value` is `true`, in which case they have linear complexity. Those entries marked "(Note C)" have constant complexity if `a.get_allocator() == rv.get_allocator()` or if either `allocator_propagate_on_move_assignment<X::allocator_type>::value` is `true` or `allocator_propagate_on_copy_assignment<X::allocator_type>::value` is `true` and linear complexity otherwise.

[ post Bellevue Howard adds: ]

> This issue was voted to WP in Bellevue, but accidently got stepped on by N2525 which was voted to WP simulataneously. Moving back to Open for the purpose of getting the wording right. The intent of this issue and N2525 are not in conflict.

[ post Sophia Antipolis Howard updated proposed wording: ]

### 677. Weaknesses in seed_seq::randomize [rand.util.seedseq]

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 Submitter: Charles Karney Opened: 2007-05-15 Last modified: 2008-09-26

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Discussion:

`seed_seq::randomize` provides a mechanism for initializing random number engines which ideally would yield "distant" states when given "close" seeds. The algorithm for `seed_seq::randomize` given in the current Working Draft for C++, N2284 (2007-05-08), has 3 weaknesses

1. Collisions in state. Because of the way the state is initialized, seeds of different lengths may result in the same state. The current version of seed_seq has the following properties:

   - For a given `s <= n`, each of the 2^(32s) seed vectors results in a distinct state.

   The proposed algorithm (below) has the considerably stronger properties:

   - All of the `(2^(32n)-1)/(2^32-1)` seed vectors of lengths `s < n` result in distinct states.
   - All of the `2^(32n)` seed vectors of length `s == n` result in distinct states.

2. Poor mixing of `v'`s entropy into the state. Consider `v.size() == n` and hold `v[n/2]` thru `v[n-1]` fixed while varying `v[0]` thru `v[n/2-1]`, a total of `2^(16n)` possibilities. Because of the simple recursion used in `seed_seq`, `begin[n/2]` thru `begin[n-1]` can take on only 2^64 possible states.

   The proposed algorithm uses a more complex recursion which results in much better mixing.

3. `seed_seq::randomize` is undefined for `v.size() == 0`. The proposed algorithm remedies this.

The current algorithm for `seed_seq::randomize` is adapted by me from the initialization procedure for the Mersenne Twister by Makoto Matsumoto and Takuji Nishimura. The weakness (2) given above was communicated to me by Matsumoto last year.

The proposed replacement for `seed_seq::randomize` is due to Mutsuo Saito, a student of Matsumoto, and is given in the implementation of the SIMD-oriented Fast Mersenne Twister random number generator SFMT. http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/index.html http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/SFMT-src-1.2.tar.gz

See Mutsuo Saito, An Application of Finite Field: Design and Implementation of 128-bit Instruction-Based Fast Pseudorandom Number Generator, Master's Thesis, Dept. of Math., Hiroshima University (Feb. 2007) http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/SFMT/M062821.pdf

One change has been made here, namely to treat the case of small `n` (setting `t = (n-1)/2` for `n < 7`).

Since `seed_seq` was introduced relatively recently there is little cost in making this incompatible improvement to it.

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 678. Changes for [rand.req.eng]

Section: X [rand.req.eng] Status: CD1 Submitter: Charles Karney Opened: 2007-05-15 Last modified: 2008-09-26

View all other issues in [rand.req.eng].

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Discussion:

Section X [rand.req.eng] Random number engine requirements:

This change follows naturally from the proposed change to `seed_seq::randomize` in 677.

In table 104 the description of `X(q)` contains a special treatment of the case `q.size() == 0`. This is undesirable for 4 reasons:

1. It replicates the functionality provided by `X()`.
2. It leads to the possibility of a collision in the state provided by some other `X(q)` with `q.size() > 0`.
3. It is inconsistent with the description of the `X(q)` in paragraphs 26.5.3.1 [rand.eng.lcong] p5, 26.5.3.2 [rand.eng.mers] p8, and 26.5.3.3 [rand.eng.sub] p10 where there is no special treatment of `q.size() == 0`.
4. The proposed replacement for `seed_seq::randomize` given above allows for the case `q.size() == 0`.

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 679. resize parameter by value

Section: 23.3 [sequences] Status: CD1 Submitter: Howard Hinnant Opened: 2007-06-11 Last modified: 2008-09-26

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Discussion:

The C++98 standard specifies that one member function alone of the containers passes its parameter (`T`) by value instead of by const reference:

>     void resize(size_type sz, T c = T());

This fact has been discussed / debated repeatedly over the years, the first time being even before C++98 was ratified. The rationale for passing this parameter by value has been:

> So that self referencing statements are guaranteed to work, for example:

> >     v.resize(v.size() + 1, v[0]);

However this rationale is not convincing as the signature for `push_back` is:

>     void push_back(const T& x);

And `push_back` has similar semantics to `resize` (append). And `push_back` must also work in the self referencing case:

>     v.push_back(v[0]);  // must work

The problem with passing `T` by value is that it can be significantly more expensive than passing by reference. The converse is also true, however when it is true it is usually far less dramatic (e.g. for scalar types).

Even with move semantics available, passing this parameter by value can be expensive. Consider for example `vector<vector<int>>`:

>     std::vector<int> x(1000);
>     std::vector<std::vector<int>> v;
>     ...
>     v.resize(v.size()+1, x);

In the pass-by-value case, `x` is copied once to the parameter of `resize`. And then internally, since the code can not know at compile time by how much `resize` is growing the `vector`, `x` is usually copied (not moved) a second time from `resize`'s parameter into its proper place within the `vector`.

With pass-by-const-reference, the `x` in the above example need be copied only once. In this case, `x` has an expensive copy constructor and so any copies that can be saved represents a significant savings.

If we can be efficient for `push_back`, we should be efficient for `resize` as well. The resize taking a reference parameter has been coded and shipped in the CodeWarrior library with no reports of problems which I am aware of.

Proposed resolution:

Change 23.3.2 [deque], p2:

>     class deque {
>        ...
>        void resize(size_type sz, const T& c);

Change 23.3.2.2 [deque.capacity], p3:

>     void resize(size_type sz, const T& c);

Change 23.3.4 [list], p2:

>     class list {
>        ...
>        void resize(size_type sz, const T& c);

Change 23.3.4.2 [list.capacity], p3:

>     void resize(size_type sz, const T& c);

Change 23.3.6 [vector], p2:

>     class vector {
>        ...
>        void resize(size_type sz, const T& c);

Change 23.3.6.2 [vector.capacity], p11:

>     void resize(size_type sz, const T& c);

### 680. move_iterator operator-> return

Section: 24.5.3.1 [move.iterator] Status: CD1 Submitter: Howard Hinnant Opened: 2007-06-11 Last modified: 2008-09-26

View all other issues in [move.iterator].

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Discussion:

`move_iterator`'s `operator->` return type `pointer` does not consistently match the type which is returned in the description in 24.5.3.3.5 [move.iter.op.ref].

>     template <class Iterator>
>     class move_iterator {
>     public:
>         ...
>         typedef typename iterator_traits<Iterator>::pointer pointer;
>         ...
>         pointer operator->() const {return current;}
>         ...
>     private:
>         Iterator current; // exposition only
>     };

There are two possible fixes.

1. `pointer operator->() const {return &*current;}`
2. `typedef Iterator pointer;`

The first solution is the one chosen by `reverse_iterator`. A potential disadvantage of this is it may not work well with iterators which return a proxy on dereference and that proxy has overloaded `operator&()`. Proxy references often need to overloaad `operator&()` to return a proxy pointer. That proxy pointer may or may not be the same type as the iterator's `pointer` type.

By simply returning the `Iterator` and taking advantage of the fact that the language forwards calls to `operator->` automatically until it finds a non-class type, the second solution avoids the issue of an overloaded `operator&()` entirely.

Proposed resolution:

Change the synopsis in 24.5.3.1 [move.iterator]:

>     typedef typename iterator_traits<Iterator>::pointer pointer;

### 681. Operator functions impossible to compare are defined in [re.submatch.op]

Section: 28.9.2 [re.submatch.op] Status: CD1 Submitter: Nozomu Katoo Opened: 2007-05-27 Last modified: 2009-05-01

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Discussion:

In 28.9.2 [re.submatch.op] of N2284, operator functions numbered 31-42 seem impossible to compare. E.g.:

>     template <class BiIter>
>        bool operator==(typename iterator_traits<BiIter>::value_type const& lhs,
>                         const sub_match<BiIter>& rhs);

> > -31- Returns: `lhs == rhs.str()`.

When `char*` is used as `BiIter`, `iterator_traits<BiIter>::value_type` would be `char`, so that `lhs == rhs.str()` ends up comparing a `char` value and an object of `std::basic_string<char>`. However, the behaviour of comparison between these two types is not defined in 21.4.8 [string.nonmembers] of N2284. This applies when `wchar_t*` is used as `BiIter`.

Proposed resolution:

Adopt the proposed resolution in N2409.

[ Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 682. basic_regex ctor takes InputIterator or ForwardIterator?

Section: 28.8.2 [re.regex.construct] Status: CD1 Submitter: Eric Niebler Opened: 2007-06-03 Last modified: 2009-05-01

View all other issues in [re.regex.construct].

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Discussion:

Looking at N2284, 28.8 [re.regex], p3 `basic_regex` class template synopsis shows this constructor:

>     template <class InputIterator>
>          basic_regex(InputIterator first, InputIterator last,
>                      flag_type f = regex_constants::ECMAScript);

In 28.8.2 [re.regex.construct], p15, the constructor appears with this signature:

>     template <class ForwardIterator>
>          basic_regex(ForwardIterator first, ForwardIterator last,
>                      flag_type f = regex_constants::ECMAScript);

`ForwardIterator` is probably correct, so the synopsis is wrong.

[ John adds: ]

> I think either could be implemented? Although an input iterator would probably require an internal copy of the string being made.

> I have no strong feelings either way, although I think my original intent was `InputIterator`.

Proposed resolution:

Adopt the proposed resolution in N2409.

[ Kona (2007): The LWG adopted the proposed resolution of N2409 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 685. reverse_iterator/move_iterator difference has invalid signatures

Section: 24.5.1.3.19 [reverse.iter.opdiff], 24.5.3.3.14 [move.iter.nonmember] Status: CD1 Submitter: Bo Persson Opened: 2007-06-10 Last modified: 2008-09-26

View all issues with CD1 status.

Discussion:

In C++03 the difference between two `reverse_iterators`

>     ri1 - ri2

is possible to compute only if both iterators have the same base iterator. The result type is the `difference_type` of the base iterator.

In the current draft, the operator is defined as 24.5.1.3.19 [reverse.iter.opdiff]

>     template<class Iterator1, class Iterator2>
>     typename reverse_iterator<Iterator>::difference_type
>        operator-(const reverse_iterator<Iterator1>& x,
>                         const reverse_iterator<Iterator2>& y);

The return type is the same as the C++03 one, based on the no longer present `Iterator` template parameter.

Besides being slightly invalid, should this operator work only when `Iterator1` and `Iterator2` has the same `difference_type`? Or should the implementation choose one of them? Which one?

The same problem now also appears in `operator-()` for `move_iterator` 24.5.3.3.14 [move.iter.nonmember].

Proposed resolution:

Change the synopsis in 24.5.1.1 [reverse.iterator]:

>     template <class Iterator1, class Iterator2>
>       typename reverse_iterator<Iterator>::difference_type auto operator-(
>         const reverse_iterator<Iterator1>& x,
>         const reverse_iterator<Iterator2>& y) -> decltype(y.current - x.current);

Change 24.5.1.3.19 [reverse.iter.opdiff]:

>     template <class Iterator1, class Iterator2>
>       typename reverse_iterator<Iterator>::difference_type auto operator-(
>         const reverse_iterator<Iterator1>& x,
>         const reverse_iterator<Iterator2>& y) -> decltype(y.current - x.current);

> > Returns: `y.current - x.current`.

Change the synopsis in 24.5.3.1 [move.iterator]:

>     template <class Iterator1, class Iterator2>
>       typename move_iterator<Iterator>::difference_type auto operator-(
>         const move_iterator<Iterator1>& x,
>         const move_iterator<Iterator2>& y) -> decltype(x.base() - y.base());

Change 24.5.3.3.14 [move.iter.nonmember]:

>     template <class Iterator1, class Iterator2>
>       typename move_iterator<Iterator>::difference_type auto operator-(
>         const move_iterator<Iterator1>& x,
>         const move_iterator<Iterator2>& y) -> decltype(x.base() - y.base());

> > Returns: `x.base() - y.base()`.

[ Pre Bellevue: This issue needs to wait until the `auto -> return` language feature goes in. ]

### 687. shared_ptr conversion constructor not constrained

Section: 20.8.15.2.1 [util.smartptr.shared.const], 20.8.15.3.1 [util.smartptr.weak.const] Status: CD1 Submitter: Peter Dimov Opened: 2007-05-10 Last modified: 2009-02-02

View all other issues in [util.smartptr.shared.const].

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Discussion:

Since all conversions from `shared_ptr<T>` to `shared_ptr<U>` have the same rank regardless of the relationship between `T` and `U`, reasonable user code that works with raw pointers fails with `shared_ptr`:

>     void f( shared_ptr<void> );
>     void f( shared_ptr<int> );

>     int main()
>     {
>       f( shared_ptr<double>() ); // ambiguous
>     }

Now that we officially have `enable_if`, we can constrain the constructor and the corresponding assignment operator to only participate in the overload resolution when the pointer types are compatible.

Proposed resolution:

In 20.8.15.2.1 [util.smartptr.shared.const], change:

> -14- Requires: For the second constructor The second constructor shall not participate in the overload resolution unless `Y*` shall be is implicitly convertible to `T*`.

In 20.8.15.3.1 [util.smartptr.weak.const], change:

>     template<class Y> weak_ptr(shared_ptr<Y> const& r);
>     weak_ptr(weak_ptr const& r);
>     template<class Y> weak_ptr(weak_ptr<Y> const& r);
>     weak_ptr(weak_ptr const& r);
>     template<class Y> weak_ptr(weak_ptr<Y> const& r);
>     template<class Y> weak_ptr(shared_ptr<Y> const& r);

> > -4- Requires: For t The second and third constructors, shall not participate in the overload resolution unless `Y*` shall be is implicitly convertible to `T*`.

### 688. reference_wrapper, cref unsafe, allow binding to rvalues

Section: 20.7.5.1 [refwrap.const] Status: WP Submitter: Peter Dimov Opened: 2007-05-10 Last modified: 2009-07-18

View all other issues in [refwrap.const].

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Discussion:

A `reference_wrapper` can be constructed from an rvalue, either by using the constructor, or via `cref` (and `ref` in some corner cases). This leads to a dangling reference being stored into the `reference_wrapper` object. Now that we have a mechanism to detect an rvalue, we can fix them to disallow this source of undefined behavior.

Also please see the thread starting at c++std-lib-17398 for some good discussion on this subject.

[ 2009-05-09 Alisdair adds: ]

> Now that `ref/cref` are constained that `T` must be an `ObjectType`, I do not believe there is any risk of binding `ref` to a temporary (which would rely on deducing `T` to be an rvalue reference type)

> However, the problem for `cref` remains, so I recommend retaining that deleted overload.

[ 2009-05-10 Howard adds: ]

> Without:

> >     template <class T> void ref(const T&& t) = delete;

> I believe this program will compile:

> >     #include <functional>

> >     struct A {};

> >     const A source() {return A();}

> >     int main()
> >     {
> >        std::reference_wrapper<const A> r = std::ref(source());
> >     }

> I.e. in:

> >     template <ObjectType T> reference_wrapper<T> ref(T& t);

> this:

> >     ref(source())

> deduces `T` as `const A`, and so:

> >     ref(const A& t)

> will bind to a temporary (tested with a pre-concepts rvalue-ref enabled compiler).

> Therefore I think we still need the ref-protection. I respectfully disagree with Alisdair's comment and am in favor of the proposed wording as it stands. Also, CWG 606 (noted below) has now been "favorably" resolved.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

In 20.7 [function.objects], add the following two signatures to the synopsis:

>     template <class T> void ref(const T&& t) = delete;
>     template <class T> void cref(const T&& t) = delete;

[ N2292 addresses the first part of the resolution but not the second. ]

[ Bellevue: Doug noticed problems with the current wording. ]

[ post Bellevue: Howard and Peter provided revised wording. ]

[ This resolution depends on a "favorable" resolution of CWG 606: that is, the "special deduction rule" is disabled with the const T&& pattern. ]

### 689. reference_wrapper constructor overly constrained

Section: 20.7.5.1 [refwrap.const] Status: CD1 Submitter: Peter Dimov Opened: 2007-05-10 Last modified: 2008-09-26

View all other issues in [refwrap.const].

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Discussion:

The constructor of `reference_wrapper` is currently `explicit`. The primary motivation behind this is the safety problem with respect to rvalues, which is addressed by the proposed resolution of the previous issue. Therefore we should consider relaxing the requirements on the constructor since requests for the implicit conversion keep resurfacing.

Also please see the thread starting at c++std-lib-17398 for some good discussion on this subject.

Proposed resolution:

Remove the `explicit` from the constructor of `reference_wrapper`. If the proposed resolution of the previous issue is accepted, remove the `explicit` from the `T&&` constructor as well to keep them in sync.

### 691. const_local_iterator cbegin, cend missing from TR1

Section: 23.5 [unord], TR1 6.3 [tr.hash] Status: CD1 Submitter: Joaquín M López Muñoz Opened: 2007-06-14 Last modified: 2008-09-26

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Discussion:

The last version of TR1 does not include the following member functions for unordered containers:

>     const_local_iterator cbegin(size_type n) const;
>     const_local_iterator cend(size_type n) const;

which looks like an oversight to me. I've checked th TR1 issues lists and the latest working draft of the C++0x std (N2284) and haven't found any mention to these menfuns or to their absence.

Is this really an oversight, or am I missing something?

Proposed resolution:

Add the following two rows to table 93 (unordered associative container requirements) in section 23.2.5 [unord.req]:

> Unordered associative container requirements (in addition to container)
> expression | return type | assertion/note pre/post-condition | complexity
> --- | --- | --- | ---
> `b.cbegin(n)` | `const_local_iterator` | `n` shall be in the range `[0, bucket_count())`. Note: `[b.cbegin(n), b.cend(n))` is a valid range containing all of the elements in the `n`th bucket. | Constant
> `b.cend(n)` | `const_local_iterator` | `n` shall be in the range `[0, bucket_count())`. | Constant

Add to the synopsis in 23.5.1 [unord.map]:

>     const_local_iterator cbegin(size_type n) const;
>     const_local_iterator cend(size_type n) const;

Add to the synopsis in 23.5.2 [unord.multimap]:

>     const_local_iterator cbegin(size_type n) const;
>     const_local_iterator cend(size_type n) const;

Add to the synopsis in 23.5.3 [unord.set]:

>     const_local_iterator cbegin(size_type n) const;
>     const_local_iterator cend(size_type n) const;

Add to the synopsis in 23.5.4 [unord.multiset]:

>     const_local_iterator cbegin(size_type n) const;
>     const_local_iterator cend(size_type n) const;

### 692. `get_money` and `put_money` should be formatted I/O functions

Section: 27.7.4 [ext.manip] Status: CD1 Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2008-09-26

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Discussion:

In a private email Bill Plauger notes:

> I believe that the function that implements `get_money` [from N2072] should behave as a formatted input function, and the function that implements `put_money` should behave as a formatted output function. This has implications regarding the skipping of whitespace and the handling of errors, among other things.

> The words don't say that right now and I'm far from convinced that such a change is editorial.

Martin's response:

> I agree that the manipulators should handle exceptions the same way as formatted I/O functions do. The text in N2072 assumes so but the Returns clause explicitly omits exception handling for the sake of brevity. The spec should be clarified to that effect.

> As for dealing with whitespace, I also agree it would make sense for the extractors and inserters involving the new manipulators to treat it the same way as formatted I/O.

Proposed resolution:

Add a new paragraph immediately above p4 of 27.7.4 [ext.manip] with the following text:

> Effects: The expression `in >> get_money(mon, intl)` described below behaves as a formatted input function (as described in 27.7.1.2.1 [istream.formatted.reqmts]).

Also change p4 of 27.7.4 [ext.manip] as follows:

> Returns: An object `s` of unspecified type such that if `in` is an object of type `basic_istream<charT, traits>` then the expression `in >> get_money(mon, intl)` behaves as a formatted input function that calls `f(in, mon, intl)` were called. The function `f` can be defined as...

[ post Bellevue: ]

> We recommend moving immediately to Review. We've looked at the issue and have a consensus that the proposed resolution is correct, but want an iostream expert to sign off. Alisdair has taken the action item to putt this up on the reflector for possible movement by Howard to Tenatively Ready.

### 693. `std::bitset::all()` missing

Section: 20.3.7 [template.bitset] Status: CD1 Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2008-09-26

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Discussion:

The `bitset` class template provides the member function `any()` to determine whether an object of the type has any bits set, and the member function `none()` to determine whether all of an object's bits are clear. However, the template does not provide a corresponding function to discover whether a `bitset` object has all its bits set. While it is possible, even easy, to obtain this information by comparing the result of `count()` with the result of `size()` for equality (i.e., via `b.count() == b.size()`) the operation is less efficient than a member function designed specifically for that purpose could be. (`count()` must count all non-zero bits in a `bitset` a word at a time while `all()` could stop counting as soon as it encountered the first word with a zero bit).

Proposed resolution:

Add a declaration of the new member function `all()` to the defintion of the `bitset` template in 20.3.7 [template.bitset], p1, right above the declaration of `any()` as shown below:

>     bool operator!=(const bitset<N>& rhs) const;
>     bool test(size_t pos) const;
>     bool all() const;
>     bool any() const;
>     bool none() const;

Add a description of the new member function to the end of 20.3.7.2 [bitset.members] with the following text:

> `bool all() const;`

> > Returns: `count() == size()`.

In addition, change the description of `any()` and `none()` for consistency with `all()` as follows:

> `bool any() const;`

> > Returns: `true` if any bit in `*this` is one `count() != 0`.

> `bool none() const;`

> > Returns: `true` if no bit in `*this` is one `count() == 0`.

### 694. `std::bitset` and `long long`

Section: 20.3.7 [template.bitset] Status: CD1 Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2008-09-26

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Discussion:

Objects of the `bitset` class template specializations can be constructed from and explicitly converted to values of the widest C++ integer type, `unsigned long`. With the introduction of `long long` into the language the template should be enhanced to make it possible to interoperate with values of this type as well, or perhaps `uintmax_t`. See c++std-lib-18274 for a brief discussion in support of this change.

Proposed resolution:

For simplicity, instead of adding overloads for `unsigned long long` and dealing with possible ambiguities in the spec, replace the `bitset` ctor that takes an `unsigned long` argument with one taking `unsigned long long` in the definition of the template as shown below. (The standard permits implementations to add overloads on other integer types or employ template tricks to achieve the same effect provided they don't cause ambiguities or changes in behavior.)

>     // [bitset.cons] constructors:
>     bitset();
>     bitset(unsigned long long val);
>     template<class charT, class traits, class Allocator>
>     explicit bitset(
>                     const basic_string<charT,traits,Allocator>& str,
>                     typename basic_string<charT,traits,Allocator>::size_type pos = 0,
>                     typename basic_string<charT,traits,Allocator>::size_type n =
>                         basic_string<charT,traits,Allocator>::npos);

Make a corresponding change in 20.3.7.1 [bitset.cons], p2:

> `bitset(unsigned long long val);`

> > Effects: Constructs an object of class bitset<N>, initializing the first `M` bit positions to the corresponding bit values in `val`. `M` is the smaller of `N` and the number of bits in the value representation (section [basic.types]) of `unsigned long long`. If `M < N` is `true`, the remaining bit positions are initialized to zero.

Additionally, introduce a new member function `to_ullong()` to make it possible to convert `bitset` to values of the new type. Add the following declaration to the definition of the template, immediate after the declaration of `to_ulong()` in 20.3.7 [template.bitset], p1, as shown below:

>     // element access:
>     bool operator[](size_t pos) const; // for b[i];
>     reference operator[](size_t pos); // for b[i];
>     unsigned long to_ulong() const;
>     unsigned long long to_ullong() const;
>     template <class charT, class traits, class Allocator>
>     basic_string<charT, traits, Allocator> to_string() const;

And add a description of the new member function to 20.3.7.2 [bitset.members], below the description of the existing `to_ulong()` (if possible), with the following text:

> `unsigned long long to_ullong() const;`

> > Throws: `overflow_error` if the integral value `x` corresponding to the bits in `*this` cannot be represented as type `unsigned long long`.

> > Returns: `x`.

### 695. ctype<char>::classic_table() not accessible

Section: 22.4.1.3 [facet.ctype.special] Status: CD1 Submitter: Martin Sebor Opened: 2007-06-22 Last modified: 2008-09-26

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Discussion:

The `ctype<char>::classic_table()` static member function returns a pointer to an array of const `ctype_base::mask` objects (enums) that contains `ctype<char>::table_size` elements. The table describes the properties of the character set in the "C" locale (i.e., whether a character at an index given by its value is alpha, digit, punct, etc.), and is typically used to initialize the `ctype<char>` facet in the classic "C" locale (the protected `ctype<char>` member function `table()` then returns the same value as `classic_table()`).

However, while `ctype<char>::table_size` (the size of the table) is a public static const member of the `ctype<char>` specialization, the `classic_table()` static member function is protected. That makes getting at the classic data less than convenient (i.e., one has to create a whole derived class just to get at the masks array). It makes little sense to expose the size of the table in the public interface while making the table itself protected, especially when the table is a constant object.

The same argument can be made for the non-static protected member function `table()`.

Proposed resolution:

Make the `ctype<char>::classic_table()` and `ctype<char>::table()` member functions public by moving their declarations into the public section of the definition of specialization in 22.4.1.3 [facet.ctype.special] as shown below:

>       static locale::id id;
>       static const size_t table_size = IMPLEMENTATION_DEFINED;
>     protected:
>       const mask* table() const throw();
>       static const mask* classic_table() throw();
>     protected:

>     ~ctype(); // virtual
>     virtual char do_toupper(char c) const;

### 696. `istream::operator>>(int&)` broken

Section: 27.7.1.2.2 [istream.formatted.arithmetic] Status: WP Submitter: Martin Sebor Opened: 2007-06-23 Last modified: 2009-10-26

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Discussion:

From message c++std-lib-17897:

The code shown in 27.7.1.2.2 [istream.formatted.arithmetic] as the "as if" implementation of the two arithmetic extractors that don't have a corresponding `num_get` interface (i.e., the `short` and `int` overloads) is subtly buggy in how it deals with `EOF`, overflow, and other similar conditions (in addition to containing a few typos).

One problem is that if `num_get::get()` reaches the EOF after reading in an otherwise valid value that exceeds the limits of the narrower type (but not `LONG_MIN` or `LONG_MAX`), it will set `err` to `eofbit`. Because of the if condition testing for `(err == 0)`, the extractor won't set `failbit` (and presumably, return a bogus value to the caller).

Another problem with the code is that it never actually sets the argument to the extracted value. It can't happen after the call to `setstate()` since the function may throw, so we need to show when and how it's done (we can't just punt as say: "it happens afterwards"). However, it turns out that showing how it's done isn't quite so easy since the argument is normally left unchanged by the facet on error except when the error is due to a misplaced thousands separator, which causes `failbit` to be set but doesn't prevent the facet from storing the value.

[ Batavia (2009-05): ]

> We believe this part of the Standard has been recently adjusted and that this issue was addressed during that rewrite.

> Move to NAD.

[ 2009-05-28 Howard adds: ]

> I've moved this issue from Tentatively NAD to Open.

> The current wording of N2857 in 22.4.2.1.2 [facet.num.get.virtuals] p3, stage 3 appears to indicate that in parsing arithmetic types, the value is always set, but sometimes in addition to setting `failbit`.

> - If there is a range error, the value is set to min or max, else
> - if there is a conversion error, the value is set to 0, else
> - if there is a grouping error, the value is set to whatever it would be if grouping were ignored, else
> - the value is set to its error-free result.

> However there is a contradictory sentence in 22.4.2.1.2 [facet.num.get.virtuals] p1.

> 27.7.1.2.2 [istream.formatted.arithmetic] should mimic the behavior of 22.4.2.1.2 [facet.num.get.virtuals] (whatever we decide that behavior is) for `int` and `short`, and currently does not. I believe that the correct code fragment should look like:

> >     typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
> >     iostate err = ios_base::goodbit;
> >     long lval;
> >     use_facet<numget>(loc).get(*this, 0, *this, err, lval);
> >     if (lval < numeric_limits<int>::min())
> >     {
> >       err |= ios_base::failbit;
> >       val = numeric_limits<int>::min();
> >     }
> >     else if (lval > numeric_limits<int>::max())
> >     {
> >       err |= ios_base::failbit;
> >       val = numeric_limits<int>::max();
> >     }
> >     else
> >       val = static_cast<int>(lval);
> >     setstate(err);

[ 2009-07 Frankfurt ]

> Move to Ready.

Proposed resolution:

Change 22.4.2.1.2 [facet.num.get.virtuals], p1:

> -1- Effects: Reads characters from `in`, interpreting them according to `str.flags()`, `use_facet<ctype<charT> >(loc)`, and `use_facet< numpunct<charT> >(loc)`, where `loc` is `str.getloc()`. If an error occurs, `val` is unchanged; otherwise it is set to the resulting value.

Change 27.7.1.2.2 [istream.formatted.arithmetic], p2 and p3:

>     operator>>(short& val);

> > -2- The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):

> > >     typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
> > >     iostate err = iostate_base::goodbit;
> > >     long lval;
> > >     use_facet<numget>(loc).get(*this, 0, *this, err, lval);
> > >     if (err != 0)
> > >       ;
> > >     else if (lval < numeric_limits<short>::min()
> > >       || numeric_limits<short>::max() < lval)
> > >          err = ios_base::failbit;
> > >     if (lval < numeric_limits<short>::min())
> > >     {
> > >       err |= ios_base::failbit;
> > >       val = numeric_limits<short>::min();
> > >     }
> > >     else if (lval > numeric_limits<short>::max())
> > >     {
> > >       err |= ios_base::failbit;
> > >       val = numeric_limits<short>::max();
> > >     }
> > >     else
> > >       val = static_cast<short>(lval);
> > >     setstate(err);

>     operator>>(int& val);

> > -3- The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):

> > >     typedef num_get<charT,istreambuf_iterator<charT,traits> > numget;
> > >     iostate err = iostate_base::goodbit;
> > >     long lval;
> > >     use_facet<numget>(loc).get(*this, 0, *this, err, lval);
> > >     if (err != 0)
> > >       ;
> > >     else if (lval < numeric_limits<int>::min()
> > >       || numeric_limits<int>::max() < lval)
> > >          err = ios_base::failbit;
> > >     if (lval < numeric_limits<int>::min())
> > >     {
> > >       err |= ios_base::failbit;
> > >       val = numeric_limits<int>::min();
> > >     }
> > >     else if (lval > numeric_limits<int>::max())
> > >     {
> > >       err |= ios_base::failbit;
> > >       val = numeric_limits<int>::max();
> > >     }
> > >     else
> > >       val = static_cast<int>(lval);
> > >     setstate(err);

### 698. `system_error` needs `const char*` constructors

Section: 19.5.5.1 [syserr.syserr.overview] Status: CD1 Submitter: Daniel Krügler Opened: 2007-06-24 Last modified: 2008-09-26

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Discussion:

In 19.5.5.1 [syserr.syserr.overview] we have the class definition of `std::system_error`. In contrast to all exception classes, which are constructible with a `what_arg string` (see 19.2 [std.exceptions], or `ios_base::failure` in 27.5.2.1.1 [ios::failure]), only overloads with with `const string&` are possible. For consistency with the re-designed remaining exception classes this class should also provide c'tors which accept a const `char* what_arg` string.

Please note that this proposed addition makes sense even considering the given implementation hint for `what()`, because `what_arg` is required to be set as `what_arg` of the base class `runtime_error`, which now has the additional c'tor overload accepting a `const char*`.

Proposed resolution:

This proposed wording assumes issue 832 has been accepted and applied to the working paper.

Change 19.5.5.1 [syserr.syserr.overview] Class system_error overview, as indicated:

>     public:
>       system_error(error_code ec, const string& what_arg);
>       system_error(error_code ec, const char* what_arg);
>       system_error(error_code ec);
>       system_error(int ev, const error_category* ecat,
>           const string& what_arg);
>       system_error(int ev, const error_category* ecat,
>           const char* what_arg);
>       system_error(int ev, const error_category* ecat);

To 19.5.5.2 [syserr.syserr.members] Class system_error members add:

>     system_error(error_code ec, const char* what_arg);

> > Effects: Constructs an object of class `system_error`.

> > Postconditions: `code() == ec` and `strcmp(runtime_error::what(), what_arg) == 0`.

>     system_error(int ev, const error_category* ecat, const char* what_arg);

> > Effects: Constructs an object of class `system_error`.

> > Postconditions: `code() == error_code(ev, ecat)` and `strcmp(runtime_error::what(), what_arg) == 0`.

### 699. N2111 changes min/max

Section: 26.5 [rand] Status: CD1 Submitter: P.J. Plauger Opened: 2007-07-01 Last modified: 2008-09-26

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Discussion:

N2111 changes `min/max` in several places in random from member functions to static data members. I believe this introduces a needless backward compatibility problem between C++0X and TR1. I'd like us to find new names for the static data members, or perhaps change `min/max` to `constexpr`s in C++0X.

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 700. N1856 defines struct `identity`

Section: 20.3.3 [forward] Status: CD1 Submitter: P.J. Plauger Opened: 2007-07-01 Last modified: 2008-09-26

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Discussion:

N1856 defines struct `identity` in `<utility>` which clashes with the traditional definition of struct `identity` in `<functional>` (not standard, but a common extension from old STL). Be nice if we could avoid this name clash for backward compatibility.

Proposed resolution:

Change 20.3.3 [forward]:

>     template <class T> struct identity
>     {
>         typedef T type;
>         const T& operator()(const T& x) const;
>     };

> >     const T& operator()(const T& x) const;

> > > Returns: `x`.

### 703. `map::at()` need a complexity specification

Section: 23.4.1.2 [map.access] Status: CD1 Submitter: Joe Gottman Opened: 2007-07-03 Last modified: 2008-09-26

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Discussion:

`map::at()` need a complexity specification.

Proposed resolution:

Add the following to the specification of `map::at()`, 23.4.1.2 [map.access]:

> Complexity: logarithmic.

### 705. type-trait `decay` incompletely specified

Section: 20.6.7 [meta.trans.other] Status: CD1 Submitter: Thorsten Ottosen Opened: 2007-07-08 Last modified: 2008-09-26

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Discussion:

The current working draft has a type-trait `decay` in 20.6.7 [meta.trans.other].

Its use is to turn C++03 pass-by-value parameters into efficient C++0x pass-by-rvalue-reference parameters. However, the current definition introduces an incompatible change where the cv-qualification of the parameter type is retained. The deduced type should loose such cv-qualification, as pass-by-value does.

Proposed resolution:

In 20.6.7 [meta.trans.other] change the last sentence:

> Otherwise the member typedef `type` equals `remove_cv<U>::type`.

In 20.5.2.4 [tuple.creation]/1 change:

> where each `Vi` in `VTypes` is `X&` if, for the corresponding type `Ti` in `Types`, `remove_cv<remove_reference<Ti>::type>::type` equals `reference_wrapper<X>`, otherwise `Vi` is `decay<Ti>::type`. Let `Ui` be `decay<Ti>::type` for each `Ti` in `Types`. Then each `Vi` in `VTypes` is `X&` if `Ui` equals `reference_wrapper<X>`, otherwise `Vi` is `Ui`.

### 706. `make_pair()` should behave as `make_tuple()` wrt. `reference_wrapper()`

Section: 20.3.4 [pairs] Status: CD1 Submitter: Thorsten Ottosen Opened: 2007-07-08 Last modified: 2008-09-26

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Discussion:

The current draft has `make_pair()` in 20.3.4 [pairs]/16 and `make_tuple()` in 20.5.2.4 [tuple.creation]. `make_tuple()` detects the presence of `reference_wrapper<X>` arguments and "unwraps" the reference in such cases. `make_pair()` would OTOH create a `reference_wrapper<X>` member. I suggest that the two functions are made to behave similar in this respect to minimize confusion.

Proposed resolution:

In 20.3 [utility] change the synopsis for make_pair() to read

>     template <class T1, class T2>
>       pair<typename decay<T1>::type V1, typename decay<T2>::type V2> make_pair(T1&&, T2&&);

In 20.3.4 [pairs]/16 change the declaration to match the above synopsis. Then change the 20.3.4 [pairs]/17 to:

> Returns: `pair<typename decay<T1>::type V1,typename decay<T2>::type V2>(forward<T1>(x),forward<T2>(y))` where `V1` and `V2` are determined as follows: Let `Ui` be `decay<Ti>::type` for each `Ti`. Then each `Vi` is `X&` if `Ui` equals `reference_wrapper<X>`, otherwise `Vi` is `Ui`.

### 709. `char_traits::not_eof` has wrong signature

Section: 21.2.3 [char.traits.specializations] Status: CD1 Submitter: Bo Persson Opened: 2007-08-13 Last modified: 2008-09-26

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Discussion:

The changes made for `constexpr` in 21.2.3 [char.traits.specializations] have not only changed the `not_eof` function from pass by const reference to pass by value, it has also changed the parameter type from `int_type` to `char_type`.

This doesn't work for type `char`, and is inconsistent with the requirements in Table 56, Traits requirements, 21.2.1 [char.traits.require].

Pete adds:

> For what it's worth, that may not have been an intentional change. N2349, which detailed the changes for adding constant expressions to the library, has strikeout bars through the `const` and the `&` that surround the `char_type` argument, but none through `char_type` itself. So the intention may have been just to change to pass by value, with text incorrectly copied from the standard.

Proposed resolution:

Change the signature in 21.2.3.1 [char.traits.specializations.char], 21.2.3.2 [char.traits.specializations.char16_t], 21.2.3.3 [char.traits.specializations.char32_t], and 21.2.3.4 [char.traits.specializations.wchar.t] to

>     static constexpr int_type not_eof(char_type int_type c);

[ Bellevue: ]

> Resolution: NAD editorial - up to Pete's judgment

[ Post Sophia Antipolis ]

> Moved from Pending NAD Editorial to Review. The proposed wording appears to be correct but non-editorial.

### 710. Missing postconditions

Section: 20.8.15.2 [util.smartptr.shared] Status: CD1 Submitter: Peter Dimov Opened: 2007-08-24 Last modified: 2008-09-26

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Discussion:

A discussion on comp.std.c++ has identified a contradiction in the `shared_ptr` specification. The `shared_ptr` move constructor and the cast functions are missing postconditions for the `get()` accessor.

[ Bellevue: ]

> Move to "ready", adopting the first (Peter's) proposed resolution.

> Note to the project editor: there is an editorial issue here. The wording for the postconditions of the casts is slightly awkward, and the editor should consider rewording "If w is the return value...", e. g. as "For a return value w...".

Proposed resolution:

Add to 20.8.15.2.1 [util.smartptr.shared.const]:

>     shared_ptr(shared_ptr&& r);
>     template<class Y> shared_ptr(shared_ptr<Y>&& r);

> > Postconditions: `*this` shall contain the old value of `r`. `r` shall be empty. `r.get() == 0`.

Add to 20.8.15.2.10 [util.smartptr.shared.cast]:

>     template<class T, class U> shared_ptr<T> static_pointer_cast(shared_ptr<U> const& r);

> > Postconditions: If `w` is the return value, `w.get() == static_cast<T*>(r.get()) && w.use_count() == r.use_count()`.

>     template<class T, class U> shared_ptr<T> dynamic_pointer_cast(shared_ptr<U> const& r);

> > Postconditions: If `w` is the return value, `w.get() == dynamic_cast<T*>(r.get())`.

>     template<class T, class U> shared_ptr<T> const_pointer_cast(shared_ptr<U> const& r);

> > Postconditions: If `w` is the return value, `w.get() == const_cast<T*>(r.get()) && w.use_count() == r.use_count()`.

Alberto Ganesh Barbati has written an alternative proposal where he suggests (among other things) that the casts be respecified in terms of the aliasing constructor as follows:

Change 20.8.15.2.10 [util.smartptr.shared.cast]:

> -2- Returns: If `r` is empty, an `empty shared_ptr<T>;` otherwise, a `shared_ptr<T>` object that stores `static_cast<T*>(r.get())` and shares ownership with `r`. `shared_ptr<T>(r, static_cast<T*>(r.get())`.

> -6- Returns:

> - When `dynamic_cast<T*>(r.get())` returns a nonzero value, a `shared_ptr<T>` object that stores a copy of it and shares ownership with `r`;
> - Otherwise, an empty `shared_ptr<T>` object.
> - If `p = dynamic_cast<T*>(r.get())` is a non-null pointer, `shared_ptr<T>(r, p);`
> - Otherwise, `shared_ptr<T>()`.

> -10- Returns: If `r` is empty, an `empty shared_ptr<T>;` otherwise, a `shared_ptr<T>` object that stores `const_cast<T*>(r.get())` and shares ownership with `r`. `shared_ptr<T>(r, const_cast<T*>(r.get())`.

This takes care of the missing postconditions for the casts by bringing in the aliasing constructor postcondition "by reference".

### 711. Contradiction in empty `shared_ptr`

Section: 20.8.15.2.5 [util.smartptr.shared.obs] Status: WP Submitter: Peter Dimov Opened: 2007-08-24 Last modified: 2009-10-26

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Discussion:

A discussion on comp.std.c++ has identified a contradiction in the `shared_ptr` specification. The note:

> [ Note: this constructor allows creation of an empty shared_ptr instance with a non-NULL stored pointer. -end note ]

after the aliasing constructor

>     template<class Y> shared_ptr(shared_ptr<Y> const& r, T *p);

reflects the intent of N2351 to, well, allow the creation of an empty `shared_ptr` with a non-NULL stored pointer.

This is contradicted by the second sentence in the Returns clause of 20.8.15.2.5 [util.smartptr.shared.obs]:

>     T* get() const;

> > Returns: the stored pointer. Returns a null pointer if `*this` is empty.

[ Bellevue: ]

> Adopt option 1 and move to review, not ready.

> There was a lot of confusion about what an empty `shared_ptr` is (the term isn't defined anywhere), and whether we have a good mental model for how one behaves. We think it might be possible to deduce what the definition should be, but the words just aren't there. We need to open an issue on the use of this undefined term. (The resolution of that issue might affect the resolution of issue 711.)

> The LWG is getting more uncomfortable with the aliasing proposal (N2351) now that we realize some of its implications, and we need to keep an eye on it, but there isn't support for removing this feature at this time.

[ Sophia Antipolis: ]

> We heard from Peter Dimov, who explained his reason for preferring solution 1.

> Because it doesn't seem to add anything. It simply makes the behavior for p = 0 undefined. For programmers who don't create empty pointers with p = 0, there is no difference. Those who do insist on creating them presumably have a good reason, and it costs nothing for us to define the behavior in this case.

> The aliasing constructor is sharp enough as it is, so "protecting" users doesn't make much sense in this particular case.

> > Do you have a use case for r being empty and r being non-null?

> I have received a few requests for it from "performance-conscious" people (you should be familiar with this mindset) who don't like the overhead of allocating and maintaining a control block when a null deleter is used to approximate a raw pointer. It is obviously an "at your own risk", low-level feature; essentially a raw pointer behind a shared_ptr facade.

> We could not agree upon a resolution to the issue; some of us thought that Peter's description above is supporting an undesirable behavior.

[ 2009-07 Frankfurt: ]

> We favor option 1, move to Ready.

> [ Howard: Option 2 commented out for clarity, and can be brought back. ]

Proposed resolution:

In keeping the N2351 spirit and obviously my preference, change 20.8.15.2.5 [util.smartptr.shared.obs]:

>     T* get() const;

> > Returns: the stored pointer. Returns a null pointer if `*this` is empty.

### 712. `seed_seq::size` no longer useful

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 Submitter: Marc Paterno Opened: 2007-08-25 Last modified: 2008-09-26

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Discussion:

One of the motivations for incorporating `seed_seq::size()` was to simplify the wording in other parts of 26.5 [rand]. As a side effect of resolving related issues, all such references to `seed_seq::size()` will have been excised. More importantly, the present specification is contradictory, as "The number of 32-bit units the object can deliver" is not the same as "the result of `v.size()`."

See N2391 and N2423 for some further discussion.

Proposed resolution:

Adopt the proposed resolution in N2423.

[ Kona (2007): The LWG adopted the proposed resolution of N2423 for this issue. The LWG voted to accelerate this issue to Ready status to be voted into the WP at Kona. ]

### 713. `sort()` complexity is too lax

Section: 25.4.1.1 [sort] Status: CD1 Submitter: Matt Austern Opened: 2007-08-30 Last modified: 2008-09-26

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Discussion:

The complexity of `sort()` is specified as "Approximately `N log(N)` (where `N == last - first` ) comparisons on the average", with no worst case complicity specified. The intention was to allow a median-of-three quicksort implementation, which is usually `O(N log N)` but can be quadratic for pathological inputs. However, there is no longer any reason to allow implementers the freedom to have a worst-cast-quadratic sort algorithm. Implementers who want to use quicksort can use a variant like David Musser's "Introsort" (Software Practice and Experience 27:983-993, 1997), which is guaranteed to be `O(N log N)` in the worst case without incurring additional overhead in the average case. Most C++ library implementers already do this, and there is no reason not to guarantee it in the standard.

Proposed resolution:

In 25.4.1.1 [sort], change the complexity to "O(N log N)", and remove footnote 266:

> Complexity: Approximately O(N log(N)) (where N == last - first ) comparisons on the average.266)

> 266) If the worst case behavior is important `stable_sort()` (25.3.1.2) or `partial_sort()` (25.3.1.3) should be used.

### 714. `search_n` complexity is too lax

Section: 25.2.12 [alg.search] Status: CD1 Submitter: Matt Austern Opened: 2007-08-30 Last modified: 2008-09-26

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Discussion:

The complexity for `search_n` (25.2.12 [alg.search] par 7) is specified as "At most (last - first ) * count applications of the corresponding predicate if count is positive, or 0 otherwise." This is unnecessarily pessimistic. Regardless of the value of count, there is no reason to examine any element in the range more than once.

Proposed resolution:

Change the complexity to "At most (last - first) applications of the corresponding predicate".

>     template<class ForwardIterator, class Size, class T>
>       ForwardIterator
>         search_n(ForwardIterator first , ForwardIterator last , Size count ,
>                  const T& value );

>     template<class ForwardIterator, class Size, class T,
>              class BinaryPredicate>
>       ForwardIterator
>         search_n(ForwardIterator first , ForwardIterator last , Size count ,
>                  const T& value , BinaryPredicate pred );

> > Complexity: At most `(last - first ) * count` applications of the corresponding predicate if `count` is positive, or 0 otherwise.

### 715. `minmax_element` complexity is too lax

Section: 25.4.7 [alg.min.max] Status: CD1 Submitter: Matt Austern Opened: 2007-08-30 Last modified: 2008-09-26

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Discussion:

The complexity for `minmax_element` (25.4.7 [alg.min.max] par 16) says "At most `max(2 * (last - first ) - 2, 0)` applications of the corresponding comparisons", i.e. the worst case complexity is no better than calling `min_element` and `max_element` separately. This is gratuitously inefficient. There is a well known technique that does better: see section 9.1 of CLRS (Introduction to Algorithms, by Cormen, Leiserson, Rivest, and Stein).

Proposed resolution:

Change 25.4.7 [alg.min.max] to:

>     template<class ForwardIterator>
>       pair<ForwardIterator, ForwardIterator>
>         minmax_element(ForwardIterator first , ForwardIterator last);
>     template<class ForwardIterator, class Compare>
>       pair<ForwardIterator, ForwardIterator>
>         minmax_element(ForwardIterator first , ForwardIterator last , Compare comp);

> > Returns: `make_pair(m, M)`, where `m` is `min_element(first, last)` or `min_element(first, last, comp)` the first iterator in `[first, last)` such that no iterator in the range refers to a smaller element, and where `M` is `max_element(first, last)` or `max_element(first, last, comp)` the last iterator in `[first, last)` such that no iterator in the range refers to a larger element.

> > Complexity: At most `max(2 * (last - first ) - 2, 0)` `max(⌊(3/2) (N-1)⌋, 0)` applications of the corresponding comparisons predicate, where `N` is `distance(first, last)`.

### 716. Production in [re.grammar] not actually modified

Section: 28.13 [re.grammar] Status: WP Submitter: Stephan T. Lavavej Opened: 2007-08-31 Last modified: 2009-10-26

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Discussion:

TR1 7.13 [tr.re.grammar]/3 and C++0x WP 28.13 [re.grammar]/3 say:

> The following productions within the ECMAScript grammar are modified as follows:

> >     CharacterClass ::
> >     [ [lookahead ∉ {^}] ClassRanges ]
> >     [ ^ ClassRanges ]

This definition for `CharacterClass` appears to be exactly identical to that in ECMA-262.

Was an actual modification intended here and accidentally omitted, or was this production accidentally included?

[ Batavia (2009-05): ]

> We agree that what is specified is identical to what ECMA-262 specifies. Pete would like to take a bit of time to assess whether we had intended, but failed, to make a change. It would also be useful to hear from John Maddock on the issue.

> Move to Open.

[ 2009-07 Frankfurt: ]

> Move to Ready.

Proposed resolution:

Remove this mention of the CharacterClass production.

>     CharacterClass ::
>     [ [lookahead ∉ {^}] ClassRanges ]
>     [ ^ ClassRanges ]

### 720. Omissions in constexpr usages

Section: 23.3.1 [array], 20.3.7 [template.bitset] Status: CD1 Submitter: Daniel Krügler Opened: 2007-08-25 Last modified: 2008-09-26

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Discussion:

1. The member function `bool array<T,N>::empty() const` should be a `constexpr` because this is easily to proof and to implement following it's operational semantics defined by Table 87 (Container requirements) which says: `a.size() == 0`.
2. The member function `bool bitset<N>::test() const` must be a `constexpr` (otherwise it would violate the specification of `constexpr bitset<N>::operator[](size_t) const`, because it's return clause delegates to `test()`).
3. I wonder how the constructor `bitset<N>::bitset(unsigned long)` can be declared as a `constexpr`. Current implementations usually have no such `bitset` c'tor which would fulfill the requirements of a `constexpr` c'tor because they have a non-empty c'tor body that typically contains for-loops or `memcpy` to compute the initialisation. What have I overlooked here?

[ Sophia Antipolis: ]

> We handle this as two parts

> 1. The proposed resolution is correct; move to ready.
> 2. The issue points out a real problem, but the issue is larger than just this solution. We believe a paper is needed, applying the full new features of C++ (including extensible literals) to update `std::bitset`. We note that we do not consider this new work, and that is should be handled by the Library Working Group.

> In order to have a consistent working paper, Alisdair and Daniel produced a new wording for the resolution.

Proposed resolution:

1. In the class template definition of 23.3.1 [array]/p. 3 change

   >     constexpr bool empty() const;

2. In the class template definition of 20.3.7 [template.bitset]/p. 1 change

   >     constexpr bool test(size_t pos ) const;

   and in 20.3.7.2 [bitset.members] change

   >     constexpr bool test(size_t pos ) const;

### 722. Missing [c.math] functions `nanf` and `nanl`

Section: 26.8 [c.math] Status: CD1 Submitter: Daniel Krügler Opened: 2007-08-27 Last modified: 2008-09-26

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Discussion:

In the listing of 26.8 [c.math], table 108: Header `<cmath>` synopsis I miss the following C99 functions (from 7.12.11.2):

>     float nanf(const char *tagp);
>     long double nanl(const char *tagp);

(Note: These functions cannot be overloaded and they are also not listed anywhere else)

Proposed resolution:

In 26.8 [c.math], table 108, section "Functions", add `nanf` and `nanl` just after the existing entry `nan`.

### 723. `basic_regex` should be moveable

Section: 28.8 [re.regex] Status: WP Submitter: Daniel Krügler Opened: 2007-08-29 Last modified: 2009-10-26

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Discussion:

Addresses UK 316

According to the current state of the standard draft, the class template `basic_regex`, as described in 28.8 [re.regex]/3, is neither `MoveConstructible` nor `MoveAssignable`. IMO it should be, because typical regex state machines tend to have a rather large data quantum and I have seen several use cases, where a factory function returns regex values, which would take advantage of moveabilities.

[ Sophia Antipolis: ]

> Needs wording for the semantics, the idea is agreed upon.

[ Post Summit Daniel updated wording to reflect new "swap rules". ]

[ 2009-07 Frankfurt: ]

> Move to Ready.

Proposed resolution:

In the class definition of `basic_regex`, just below 28.8 [re.regex]/3, perform the following changes:

1. Just after `basic_regex(const basic_regex&);` insert:

   >     basic_regex(basic_regex&&);

2. Just after `basic_regex& operator=(const basic_regex&);` insert:

   >     basic_regex& operator=(basic_regex&&);

3. Just after `basic_regex& assign(const basic_regex& that);` insert:

   >     basic_regex& assign(basic_regex&& that);

4. In 28.8.2 [re.regex.construct], just after p.11 add the following new member definition:

   >     basic_regex(basic_regex&& e);

   > > Effects: Move-constructs a `basic_regex` instance from `e`.

   > > Postconditions: `flags()` and `mark_count()` return `e.flags()` and `e.mark_count()`, respectively, that `e` had before construction, leaving `e` in a valid state with an unspecified value.

   > > Throws: nothing.

5. Also in 28.8.2 [re.regex.construct], just after p.18 add the following new member definition:

   >     basic_regex& operator=(basic_regex&& e);

   > > Effects: Returns the result of `assign(std::move(e))`.

6. In 28.8.3 [re.regex.assign], just after p. 2 add the following new member definition:

   >     basic_regex& assign(basic_regex&& rhs);

   > > Effects: Move-assigns a `basic_regex` instance from `rhs` and returns `*this`.

   > > Postconditions: `flags()` and `mark_count()` return `rhs.flags()` and `rhs.mark_count()`, respectively, that `rhs` had before assignment, leaving `rhs` in a valid state with an unspecified value.

   > > Throws: nothing.

### 728. Problem in [rand.eng.mers]/6

Section: 26.5.3.2 [rand.eng.mers] Status: CD1 Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-09-26

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Discussion:

The `mersenne_twister_engine` is required to use a seeding method that is given as an algorithm parameterized over the number of bits `W`. I doubt whether the given generalization of an algorithm that was originally developed only for unsigned 32-bit integers is appropriate for other bit widths. For instance, `W` could be theoretically 16 and `UIntType` a 16-bit integer, in which case the given multiplier would not fit into the `UIntType`. Moreover, T. Nishimura and M. Matsumoto have chosen a dif ferent multiplier for their 64 bit Mersenne Twister [reference].

I see two possible resolutions:

1. Restrict the parameter `W` of the `mersenne_twister_template` to values of 32 or 64 and use the multiplier from [the above reference] for the 64-bit case (my preference)
2. Interpret the state array for any `W` as a 32-bit array of appropriate length (and a specified byte order) and always employ the 32-bit algorithm for seeding

See N2424 for further discussion.

[ Bellevue: ]

> Stephan Tolksdorf has additional comments on N2424. He comments: "there is a typo in the required behaviour for mt19937_64: It should be the 10000th (not 100000th) invocation whose value is given, and the value should be 9981545732273789042 (not 14002232017267485025)." These values need checking.

> Take the proposed recommendation in N2424 and move to REVIEW.

Proposed resolution:

See N2424 for the proposed resolution.

[ Stephan Tolksdorf adds pre-Bellevue: ]

> I support the proposed resolution in N2424, but there is a typo in the required behaviour for `mt19937_64`: It should be the 10000th (not 100000th) invocation whose value is given, and the value should be 9981545732273789042 (not 14002232017267485025). The change to para. 8 proposed by Charles Karney should also be included in the proposed wording.

[ Sophia Antipolis: ]

> Note the main part of the issue is resolved by N2424.

### 734. Unnecessary restriction in [rand.dist.norm.chisq]

Section: 26.5.8.4.3 [rand.dist.norm.chisq] Status: CD1 Submitter: Stephan Tolksdorf Opened: 2007-09-21 Last modified: 2008-09-26

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Discussion:

`chi_squared_distribution`, `fisher_f_distribution` and `student_t_distribution` have parameters for the "degrees of freedom" `n` and `m` that are specified as integers. For the following two reasons this is an unnecessary restriction: First, in many applications such as Bayesian inference or Monte Carlo simulations it is more convenient to treat the respective param- eters as continuous variables. Second, the standard non-naive algorithms (i.e. O(1) algorithms) for simulating from these distributions work with floating-point parameters anyway (all three distributions could be easily implemented using the Gamma distribution, for instance).

Similar arguments could in principle be made for the parameters `t` and `k` of the discrete `binomial_distribution` and `negative_binomial_distribution`, though in both cases continuous parameters are less frequently used in practice and in case of the `binomial_distribution` the implementation would be significantly complicated by a non-discrete parameter (in most implementations one would need an approximation of the log-gamma function instead of just the log-factorial function).

Possible resolution: For these reasons, I propose to change the type of the respective parameters to double.

[ Bellevue: ]

> In N2424. Not wildly enthusiastic, not really felt necessary. Less frequently used in practice. Not terribly bad either. Move to OPEN.

[ Sophia Antipolis: ]

> Marc Paterno: The generalizations were explicitly left out when designing the facility. It's harder to test.

> Marc Paterno: Ask implementers whether floating-point is a significant burden.

> Alisdair: It's neater to do it now, do ask Bill Plauger.

> Disposition: move to review with the option for "NAD" if it's not straightforward to implement; unanimous consent.

Proposed resolution:

See N2424 for the proposed resolution.

[ Stephan Tolksdorf adds pre-Bellevue: ]

> In 26.5.8.4.3 [rand.dist.norm.chisq]:

> > Delete ", where `n` is a positive integer" in the first paragraph.

> > Replace both occurrences of "`explicit chi_squared_distribution(int n = 1);`" with "`explicit chi_squared_distribution(RealType n = 1);`".

> > Replace both occurrences of "`int n() const;`" with "`RealType n() const;`".

> In 26.5.8.4.5 [rand.dist.norm.f]:

> > Delete ", where `m` and `n` are positive integers" in the first paragraph.

> > Replace both occurrences of

> > >     explicit fisher_f_distribution(int m = 1, int n = 1);

> > with

> > >     explicit fisher_f_distribution(RealType m = 1, RealType n = 1);

> > Replace both occurrences of "`int m() const;" with "RealType m() const;`".

> > Replace both occurrences of "`int n() const;" with "RealType n() const;`".

> In 26.5.8.4.6 [rand.dist.norm.t]:

> > Delete ", where `n` is a positive integer" in the first paragraph.

> > Replace both occurrences of "`explicit student_t_distribution(int n = 1);`" with "`explicit student_t_distribution(RealType n = 1);`".

> > Replace both occurrences of "`int n() const;`" with "`RealType n() const;`".

### 740. Please remove `*_ptr<T[N]>`

Section: X [unique.ptr.compiletime] Status: CD1 Submitter: Herb Sutter Opened: 2007-10-04 Last modified: 2008-09-26

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Discussion:

Please don't provide `*_ptr<T[N]>`. It doesn't enable any useful bounds-checking (e.g., you could imagine that doing `op++` on a `shared_ptr<T[N]>` yields a `shared_ptr<T[N-1]>`, but that promising path immediately falters on `op--` which can't reliably dereference because we don't know the lower bound). Also, most buffers you'd want to point to don't have a compile-time known size.

To enable any bounds-checking would require run-time information, with the usual triplet: base (lower bound), current offset, and max offset (upper bound). And I can sympathize with the point of view that you wouldn't want to require this on `*_ptr` itself. But please let's not follow the `<T[N]>` path, especially not with additional functions to query the bounds etc., because this sets wrong user expectations by embarking on a path that doesn't go all the way to bounds checking as it seems to imply.

If bounds checking is desired, consider a `checked_*_ptr` instead (e.g., `checked_shared_ptr`). And make the interfaces otherwise identical so that user code could easily `#define/typedef` between prepending `checked_` on debug builds and not doing so on release builds (for example).

Note that some may object that `checked_*_ptr` may seem to make the smart pointer more like `vector`, and we don't want two ways to spell `vector`. I don't agree, but if that were true that would be another reason to remove `*_ptr<T[N]>` which equally makes the smart pointer more like `std::array.` :-)

[ Bellevue: ]

> Suggestion that fixed-size array instantiations are going to fail at compile time anyway (if we remove specialization) due to pointer decay, at least that appears to be result from available compilers.

> So concerns about about requiring static_assert seem unfounded.

> After a little more experimentation with compiler, it appears that fixed size arrays would only work at all if we supply these explicit specialization. So removing them appears less breaking than originally thought.

> straw poll unanimous move to Ready.

Proposed resolution:

Change the synopsis under 20.8.14 [unique.ptr] p2:

>     ...
>     template<class T> struct default_delete;
>     template<class T> struct default_delete<T[]>;
>     template<class T, size_t N> struct default_delete<T[N]>;

>     template<class T, class D = default_delete<T>> class unique_ptr;
>     template<class T, class D> class unique_ptr<T[], D>;
>     template<class T, class D, size_t N> class unique_ptr<T[N], D>;
>     ...

Remove the entire section [unique.ptr.dltr.dflt2] `default_delete<T[N]>`.

Remove the entire section X [unique.ptr.compiletime] `unique_ptr` for array objects with a compile time length and its subsections: [unique.ptr.compiletime.dtor], [unique.ptr.compiletime.observers], [unique.ptr.compiletime.modifiers].

### 743. rvalue `swap` for `shared_ptr`

Section: 20.8.15.2.9 [util.smartptr.shared.spec] Status: CD1 Submitter: Howard Hinnant Opened: 2007-10-10 Last modified: 2008-09-26

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Discussion:

When the LWG looked at 674 in Kona the following note was made:

> We may need to open an issue to deal with the question of whether `shared_ptr` needs an rvalue `swap`.

This issue was opened in response to that note.

I believe allowing rvalue `shared_ptr`s to `swap` is both appropriate, and consistent with how other library components are currently specified.

[ Bellevue: ]

> Concern that the three signatures for swap is needlessly complicated, but this issue merely brings shared_ptr into equal complexity with the rest of the library. Will open a new issue for concern about triplicate signatures.

> Adopt issue as written.

Proposed resolution:

Change the synopsis in 20.8.15.2 [util.smartptr.shared]:

>     void swap(shared_ptr&& r);
>     ...
>     template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b);
>     template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b);
>     template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);

Change 20.8.15.2.4 [util.smartptr.shared.mod]:

>     void swap(shared_ptr&& r);

Change 20.8.15.2.9 [util.smartptr.shared.spec]:

>     template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b);
>     template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b);
>     template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);

### 744. What is the lifetime of an exception pointed to by an exception_ptr?

Section: 18.8.5 [propagation] Status: CD1 Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2008-09-26

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Discussion:

Without some lifetime guarantee, it is hard to know how this type can be used. Very specifically, I don't see how the current wording would guarantee and exception_ptr caught at the end of one thread could be safely stored and rethrown in another thread - the original motivation for this API.

(Peter Dimov agreed it should be clearer, maybe a non-normative note to explain?)

[ Bellevue: ]

> Agree the issue is real.

> Intent is lifetime is similar to a shared_ptr (and we might even want to consider explicitly saying that it is a shared_ptr< unspecified type >).

> We expect that most implementations will use shared_ptr, and the standard should be clear that the exception_ptr type is intended to be something whose semantics are smart-pointer-like so that the user does not need to worry about lifetime management. We still need someone to draught those words - suggest emailing Peter Dimov.

> Move to Open.

Proposed resolution:

Change 18.8.5 [propagation]/7:

> -7- Returns: An `exception_ptr` object that refers to the currently handled exception or a copy of the currently handled exception, or a null `exception_ptr` object if no exception is being handled. The referenced object remains valid at least as long as there is an `exception_ptr` that refers to it. If the function needs to allocate memory and the attempt fails, it returns an `exception_ptr` object that refers to an instance of `bad_alloc`. It is unspecified whether the return values of two successive calls to `current_exception` refer to the same exception object. [Note: that is, it is unspecified whether `current_exception` creates a new copy each time it is called. --end note]

### 746. current_exception may fail with bad_alloc

Section: 18.8.5 [propagation] Status: CD1 Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2008-09-26

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Discussion:

I understand that the attempt to copy an exception may run out of memory, but I believe this is the only part of the standard that mandates failure with specifically `bad_alloc`, as opposed to allowing an implementation-defined type derived from `bad_alloc`. For instance, the Core language for a failed new expression is:

> Any other allocation function that fails to allocate storage shall indicate failure only by throwing an exception of a type that would match a handler (15.3) of type `std::bad_alloc` (18.5.2.1).

I think we should allow similar freedom here (or add a blanket compatible-exception freedom paragraph in 17)

I prefer the clause 17 approach myself, and maybe clean up any outstanding wording that could also rely on it.

Although filed against a specific case, this issue is a problem throughout the library.

[ Bellevue: ]

> Is issue bigger than library?

> No - Core are already very clear about their wording, which is inspiration for the issue.

> While not sold on the original 18.7.5 use case, the generalised 17.4.4.8 wording is the real issue.

> Accept the broad view and move to ready

Proposed resolution:

Add the following exemption clause to 17.6.4.11 [res.on.exception.handling]:

> A function may throw a type not listed in its Throws clause so long as it is derived from a class named in the Throws clause, and would be caught by an exception handler for the base type.

### 749. Currently `has_nothrow_copy_constructor<T>::value` is true if T has 'a' nothrow copy constructor.

Section: 20.6.4.3 [meta.unary.prop] Status: CD1 Submitter: Alisdair Meredith Opened: 2007-10-10 Last modified: 2008-09-26

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Discussion:

Unfortunately a class can have multiple copy constructors, and I believe to be useful this trait should only return true is ALL copy constructors are no-throw.

For instance:

>     struct awkward {
>      awkward( const awkward & ) throw() {}
>      awkward( awkward & ) { throw "oops"; } };

Proposed resolution:

Change 20.6.4.3 [meta.unary.prop]:

>     has_trivial_copy_constructor

> > `T` is a trivial type (3.9) or a reference type or a class type with a trivial copy constructor where all copy constructors are trivial (12.8).

>     has_trivial_assign

> > `T` is neither `const` nor a reference type, and `T` is a trivial type (3.9) or a class type with a trivial copy assignment operator where all copy assignment operators are trivial (12.8).

>     has_nothrow_copy_constructor

> > `has_trivial_copy_constructor<T>::value` is `true` or `T` is a class type with a where all copy constructors that is are known not to throw any exceptions or `T` is an array of such a class type

>     has_nothrow_assign

> > `T` is neither `const` nor a reference type, and `has_trivial_assign<T>::value` is `true` or `T` is a class type with a where all copy assignment operators take ing an lvalue of type `T` that is known not to throw any exceptions or `T` is an array of such a class type.

### 752. Allocator complexity requirement

Section: 20.2.2 [allocator.requirements] Status: WP Submitter: Hans Boehm Opened: 2007-10-11 Last modified: 2009-03-09

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Discussion:

Did LWG recently discuss 20.2.2 [allocator.requirements]-2, which states that "All the operations on the allocators are expected to be amortized constant time."?

As I think I pointed out earlier, this is currently fiction for `allocate()` if it has to obtain memory from the OS, and it's unclear to me how to interpret this for `construct()` and `destroy()` if they deal with large objects. Would it be controversial to officially let these take time linear in the size of the object, as they already do in real life?

`Allocate()` more blatantly takes time proportional to the size of the object if you mix in GC. But it's not really a new problem, and I think we'd be confusing things by leaving the bogus requirements there. The current requirement on `allocate()` is generally not important anyway, since it takes O(size) to construct objects in the resulting space. There are real performance issues here, but they're all concerned with the constants, not the asymptotic complexity.

Proposed resolution:

Change 20.2.2 [allocator.requirements]/2:

> -2- Table 39 describes the requirements on types manipulated through allocators. All the operations on the allocators are expected to be amortized constant time. Table 40 describes the requirements on allocator types.

### 753. Move constructor in draft

Section: 20.2.1 [utility.arg.requirements] Status: WP Submitter: Yechezkel Mett Opened: 2007-10-14 Last modified: 2009-03-09

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Discussion:

The draft standard n2369 uses the term move constructor in a few places, but doesn't seem to define it.

`MoveConstructible` requirements are defined in Table 33 in 20.2.1 [utility.arg.requirements] as follows:

> `MoveConstructible` requirements
> expression | post-condition
> --- | ---
> `T t = rv` | `t` is equivalent to the value of `rv` before the construction
> [Note: There is no requirement on the value of `rv` after the construction. -- end note]

(where `rv` is a non-const rvalue of type `T`).

So I assume the move constructor is the constructor that would be used in filling the above requirement.

For `vector::reserve`, `vector::resize` and the `vector` modifiers given in 23.3.6.4 [vector.modifiers] we have

> Requires: If `value_type` has a move constructor, that constructor shall not throw any exceptions.

Firstly "If `value_type` has a move constructor" is superfluous; every type which can be put into a `vector` has a move constructor (a copy constructor is also a move constructor). Secondly it means that for any `value_type` which has a throwing copy constructor and no other move constructor these functions cannot be used -- which I think will come as a shock to people who have been using such types in `vector` until now!

I can see two ways to correct this. The simpler, which is presumably what was intended, is to say "If `value_type` has a move constructor and no copy constructor, the move constructor shall not throw any exceptions" or "If `value_type` has a move constructor which changes the value of its parameter,".

The other alternative is add to `MoveConstructible` the requirement that the expression does not throw. This would mean that not every type that satisfies the `CopyConstructible` requirements also satisfies the `MoveConstructible` requirements. It would mean changing requirements in various places in the draft to allow either `MoveConstructible` or `CopyConstructible`, but I think the result would be clearer and possibly more concise too.

Proposed resolution:

Add new defintions to 17.3 [definitions]:

> move constructor

> a constructor which accepts only rvalue arguments of that type, and modifies the rvalue as a side effect during the construction.

> move assignment operator

> an assignment operator which accepts only rvalue arguments of that type, and modifies the rvalue as a side effect during the assignment.

> move assignment

> use of the move assignment operator.

[ Howard adds post-Bellevue: ]

> Unfortunately I believe the wording recommended by the LWG in Bellevue is incorrect. `reserve` et. al. will use a move constructor if one is available, else it will use a copy constructor. A type may have both. If the move constructor is used, it must not throw. If the copy constructor is used, it can throw. The sentence in the proposed wording is correct without the recommended insertion. The Bellevue LWG recommended moving this issue to Ready. I am unfortunately pulling it back to Open. But I'm drafting wording to atone for this egregious action. :-)

### 755. `std::vector` and `std:string` lack explicit shrink-to-fit operations

Section: 23.3.6.2 [vector.capacity], 21.4.4 [string.capacity] Status: CD1 Submitter: Beman Dawes Opened: 2007-10-31 Last modified: 2008-09-26

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Discussion:

A `std::vector` can be shrunk-to-fit via the swap idiom:

>     vector<int> v;
>     ...
>     v.swap(vector<int>(v));  // shrink to fit

> > or:

>     vector<int>(v).swap(v);  // shrink to fit

> > or:

>     swap(v, vector<int>(v));  // shrink to fit

A non-binding request for shrink-to-fit can be made to a `std::string` via:

>     string s;
>     ...
>     s.reserve(0);

Neither of these is at all obvious to beginners, and even some experienced C++ programmers are not aware that shrink-to-fit is trivially available.

Lack of explicit functions to perform these commonly requested operations makes vector and string less usable for non-experts. Because the idioms are somewhat obscure, code readability is impaired. It is also unfortunate that two similar vector-like containers use different syntax for the same operation.

The proposed resolution addresses these concerns. The proposed function takes no arguments to keep the solution simple and focused.

Proposed resolution:

To Class template basic_string 21.4 [basic.string] synopsis, Class template vector 23.3.6 [vector] synopsis, and Class vector<bool> 23.3.7 [vector.bool] synopsis, add:

>     void shrink_to_fit();

To basic_string capacity 21.4.4 [string.capacity] and vector capacity 23.3.6.2 [vector.capacity], add:

>     void shrink_to_fit();

> > Remarks: `shrink_to_fit` is a non-binding request to reduce `capacity()` to `size()`. [Note: The request is non-binding to allow latitude for implementation-specific optimizations. -- end note]

[ 850 has been added to deal with this issue with respect to `deque`. ]

### 758. `shared_ptr` and `nullptr`

Section: 20.8.15.2 [util.smartptr.shared] Status: WP Submitter: Joe Gottman Opened: 2007-10-31 Last modified: 2009-03-09

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Discussion:

Consider the following program:

>     int main() {
>        shared_ptr<int> p(nullptr);
>        return 0;
>     }

This program will fail to compile because `shared_ptr` uses the following template constructor to construct itself from pointers:

>     template <class Y> shared_ptr(Y *);

According to N2431, the conversion from `nullptr_t` to `Y *` is not deducible, so the above constructor will not be found. There are similar problems with the constructors that take a pointer and a `deleter` or a pointer, a `deleter` and an allocator, as well as the corresponding forms of `reset()`. Note that N2435 will solve this problem for constructing from just `nullptr`, but not for constructors that use `deleters` or allocators or for `reset()`.

In the case of the functions that take deleters, there is the additional question of what argument should be passed to the deleter when it is eventually called. There are two reasonable possibilities: `nullptr` or `static_cast<T *>(0)`, where `T` is the template argument of the `shared_ptr`. It is not immediately clear which of these is better. If `D::operator()` is a template function similar to `shared_ptr`'s constructor, then `d(static_cast<T*>(0))` will compile and `d(nullptr)` will not. On the other hand, if `D::operator()()` takes a parameter that is a pointer to some type other that `T` (for instance `U*` where `U` derives from `T`) then `d(nullptr)` will compile and `d(static_cast<T *>(0))` may not.

[ Bellevue: ]

> The general idea is right, we need to be able to pass a nullptr to a shared_ptr, but there are a few borderline editorial issues here. (For example, the single-argument nullptr_t constructor in the class synopsis isn't marked explicit, but it is marked explicit in the proposed wording for 20.6.6.2.1. There is a missing empty parenthesis in the form that takes a nullptr_t, a deleter, and an allocator.)

> More seriously: this issue says that a shared_ptr constructed from a nullptr is empty. Since "empty" is undefined, it's hard to know whether that's right. This issue is pending on handling that term better.

> Peter suggests definition of empty should be "does not own anything"

> Is there an editorial issue that post-conditions should refer to get() = nullptr, rather than get() = 0?

> No strong feeling towards accept or NAD, but prefer to make a decision than leave it open.

> Seems there are no technical merits between NAD and Ready, comes down to "Do we intentially want to allow/disallow null pointers with these functions". Staw Poll - support null pointers 5 - No null pointers 0

> Move to Ready, modulo editorial comments

[ post Bellevue Peter adds: ]

> The following wording changes are less intrusive:

> In 20.8.15.2.1 [util.smartptr.shared.const], add:

> >     shared_ptr(nullptr_t);

> after:

> >     shared_ptr();

> (Absence of explicit intentional.)

> `px.reset( nullptr )` seems a somewhat contrived way to write `px.reset()`, so I'm not convinced of its utility.

> It's similarly not clear to me whether the deleter constructors need to be extended to take `nullptr`, but if they need to:

> Add

> >     template<class D> shared_ptr(nullptr_t p, D d);
> >     template<class D, class A> shared_ptr(nullptr_t p, D d, A a);

> after

> >     template<class Y, class D> shared_ptr(Y* p, D d);
> >     template<class Y, class D, class A> shared_ptr(Y* p, D d, A a);

> Note that this changes the semantics of the new constructors such that they consistently call `d(p)` instead of `d((T*)0)` when `p` is `nullptr`.

> The ability to be able to pass `0/NULL` to a function that takes a `shared_ptr` has repeatedly been requested by users, but the other additions that the proposed resolution makes are not supported by real world demand or motivating examples.

> It might be useful to split the obvious and non-controversial `nullptr_t` constructor into a separate issue. Waiting for "empty" to be clarified is unnecessary; this is effectively an alias for the default constructor.

[ Sophia Antipolis: ]

> We want to remove the reset functions from the proposed resolution.

> The remaining proposed resolution text (addressing the constructors) are wanted.

> Disposition: move to review. The review should check the wording in the then-current working draft.

Proposed resolution:

In 20.8.15.2 [util.smartptr.shared] p4, add to the definition/synopsis of `shared_ptr`:

>     template<class D> shared_ptr(nullptr_t p, D d);
>     template<class D, class A> shared_ptr(nullptr_t p, D d, A a);

after

>     template<class Y, class D> shared_ptr(Y* p, D d);
>     template<class Y, class D, class A> shared_ptr(Y* p, D d, A a);

In 20.8.15.2.1 [util.smartptr.shared.const] add:

>     template<class D> shared_ptr(nullptr_t p, D d);
>     template<class D, class A> shared_ptr(nullptr_t p, D d, A a);

after

>     template<class Y, class D> shared_ptr(Y* p, D d);
>     template<class Y, class D, class A> shared_ptr(Y* p, D d, A a);

(reusing the following paragraphs 20.8.15.2.1 [util.smartptr.shared.const]/9-13 that speak of p.)

In 20.8.15.2.1 [util.smartptr.shared.const]/10, change

> Effects: Constructs a `shared_ptr` object that owns the pointer object `p` and the deleter `d`. The second constructor shall use a copy of `a` to allocate memory for internal use.

Rationale:

[ San Francisco: ]

> "pointer" is changed to "object" to handle the fact that nullptr_t isn't a pointer.

### 759. A reference is not an object

Section: 23.2 [container.requirements] Status: CD1 Submitter: Jens Maurer Opened: 2007-11-06 Last modified: 2008-09-26

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Discussion:

23.2 [container.requirements] says:

> -12- Objects passed to member functions of a container as rvalue references shall not be elements of that container. No diagnostic required.

A reference is not an object, but this sentence appears to claim so.

What is probably meant here:

> An object bound to an rvalue reference parameter of a member function of a container shall not be an element of that container; no diagnostic required.

Proposed resolution:

Change 23.2 [container.requirements]:

> -12- Objects passed to member functions of a container as rvalue references shall not be elements An object bound to an rvalue reference parameter of a member function of a container shall not be an element of that container.; N no diagnostic required.

### 761. `unordered_map` needs an `at()` member function

Section: 23.5.1.2 [unord.map.elem] Status: CD1 Submitter: Joe Gottman Opened: 2007-11-15 Last modified: 2008-09-26

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Discussion:

The new member function `at()` was recently added to `std::map()`. It acts like `operator[]()`, except it throws an exception when the input key is not found. It is useful when the `map` is `const`, the `value_type` of the key doesn't have a default constructor, it is an error if the key is not found, or the user wants to avoid accidentally adding an element to the map. For exactly these same reasons, `at()` would be equally useful in `std::unordered_map`.

Proposed resolution:

Add the following functions to the definition of `unordered_map` under "lookup" (23.5.1 [unord.map]):

>     mapped_type& at(const key_type& k);
>     const mapped_type &at(const key_type &k) const;

Add the following definitions to 23.5.1.2 [unord.map.elem]:

>     mapped_type& at(const key_type& k);
>     const mapped_type &at(const key_type &k) const;

> > Returns: A reference to `x.second`, where `x` is the (unique) element whose key is equivalent to `k`.

> > Throws: An exception object of type `out_of_range` if no such element is present.

[ Bellevue: Editorial note: the "(unique)" differs from map. ]

### 762. `std::unique_ptr` requires complete type?

Section: 20.8.14 [unique.ptr] Status: CD1 Submitter: Daniel Krügler Opened: 2007-11-30 Last modified: 2008-09-26

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Discussion:

In contrast to the proposed `std::shared_ptr`, `std::unique_ptr` does currently not support incomplete types, because it gives no explicit grant - thus instantiating `unique_ptr` with an incomplete pointee type `T` automatically belongs to undefined behaviour according to 17.6.3.8 [res.on.functions]/2, last bullet. This is an unnecessary restriction and prevents many well-established patterns - like the bridge pattern - for `std::unique_ptr`.

[ Bellevue: ]

> Move to open. The LWG is comfortable with the intent of allowing incomplete types and making `unique_ptr` more like `shared_ptr`, but we are not comfortable with the wording. The specification for `unique_ptr` should be more like that of `shared_ptr`. We need to know, for individual member functions, which ones require their types to be complete. The `shared_ptr` specification is careful to say that for each function, and we need the same level of care here. We also aren't comfortable with the "part of the operational semantic" language; it's not used elsewhere in the standard, and it's not clear what it means. We need a volunteer to produce new wording.

Proposed resolution:

The proposed changes in the following revision refers to the current state of N2521 including the assumption that X [unique.ptr.compiletime] will be removed according to the current state of 740.

The specialization `unique_ptr<T[]>` has some more restrictive constraints on type-completeness on `T` than `unique_ptr<T>`. The following proposed wordings try to cope with that. If the committee sees less usefulness on relaxed constraints on `unique_ptr<T[]>`, the alternative would be to stop this relaxation e.g. by adding one further bullet to 20.8.14.3 [unique.ptr.runtime]/1: "`T` shall be a complete type, if used as template argument of `unique_ptr<T[], D>`

This issue has some overlap with 673, but it seems not to cause any problems with this one, because 673 adds only optional requirements on `D` that do not conflict with the here discussed ones, provided that `D::pointer`'s operations (including default construction, copy construction/assignment, and pointer conversion) are specified not to throw, otherwise this would have impact on the current specification of `unique_ptr`.

1. In 20.8.14 [unique.ptr]/2 add as the last sentence to the existing para:

   > The `unique_ptr` provides a semantics of strict ownership. A `unique_ptr` owns the object it holds a pointer to. A `unique_ptr` is not `CopyConstructible`, nor `CopyAssignable`, however it is `MoveConstructible` and `MoveAssignable`. The template parameter `T` of `unique_ptr` may be an incomplete type. [ Note: The uses of `unique_ptr` include providing exception safety for dynamically allcoated memory, passing ownership of dynamically allocated memory to a function, and returning dynamically allocated memory from a function. -- end note ]

2. 20.8.14.2.1 [unique.ptr.single.ctor]/1: No changes necessary.

   > [ N.B.: We only need the requirement that `D` is `DefaultConstructible`. The current wording says just this. ]

3. In 20.8.14.2.1 [unique.ptr.single.ctor]/5 change the requires clause to say:

   > Requires: The expression `D()(p)` shall be well formed. The default constructor of `D` shall not throw an exception. `D` must not be a reference type. `D` shall be default constructible, and that construction shall not throw an exception.

   > [ N.B.: There is no need that the expression `D()(p)` is well-formed at this point. I assume that the current wording is based on the corresponding `shared_ptr` wording. In case of `shared_ptr` this requirement is necessary, because the corresponding c'tor *can* fail and must invoke delete `p/d(p)` in this case. `Unique_ptr` is simpler in this regard. The *only* functions that must insist on well-formedness and well-definedness of the expression `get_deleter()(get())` are (1) the destructor and (2) `reset`. The reasoning for the wording change to explicitly require `DefaultConstructible` of `D` is to guarantee that invocation of `D`'s default c'tor is both well-formed and well-defined. Note also that we do *not* need the requirement that `T` must be complete, also in contrast to `shared_ptr`. `Shared_ptr` needs this, because it's c'tor is a template c'tor which potentially requires `Convertible<Y*, X*>`, which again requires Completeness of `Y`, if `!SameType<X, Y>` ]

4. Merge 20.8.14.2.1 [unique.ptr.single.ctor]/12+13 thereby removing the sentence of 12, but transferring the "requires" to 13:

   > Requires: If `D` is not an lvalue-reference type then[..]

   > [ N.B.: For the same reasons as for (3), there is no need that `d(p)` is well-formed/well-defined at this point. The current wording guarantees all what we need, namely that the initialization of both the `T*` pointer and the `D` deleter are well-formed and well-defined. ]

5. 20.8.14.2.1 [unique.ptr.single.ctor]/17: No changes necessary.

6. 20.8.14.2.1 [unique.ptr.single.ctor]/21:

   > Requires: If `D` is not a reference type, construction of the deleter `D` from an rvalue of type `E` shall be well formed and shall not throw an exception. If `D` is a reference type, then `E` shall be the same type as `D` (diagnostic required). `U*` shall be implicitly convertible to `T*`. [Note: These requirements imply that `T` and `U` be complete types. -- end note]

   [ N.B.: The current wording of 21 already implicitly guarantees that `U` is completely defined, because it requires that `Convertible<U*, T*>` is true. If the committee wishes this explicit requirement can be added, e.g. "`U` shall be a complete type." ]

7. 20.8.14.2.2 [unique.ptr.single.dtor]: Just before p1 add a new paragraph:

   > Requires: The expression `get_deleter()(get())` shall be well-formed, shall have well-defined behavior, and shall not throw exceptions. [Note: The use of `default_delete` requires `T` to be a complete type. -- end note]

   > [ N.B.: This requirement ensures that the whole responsibility on type-completeness of `T` is delegated to this expression. ]

8. 20.8.14.2.3 [unique.ptr.single.asgn]/1: No changes necessary, except the current editorial issue, that "must shall" has to be changed to "shall", but this change is not a special part of this resolution.

   [ N.B. The current wording is sufficient, because we can delegate all further requirements on the requirements of the effects clause ]

9. 20.8.14.2.3 [unique.ptr.single.asgn]/6:

   > Requires: Assignment of the deleter `D` from an rvalue `D` shall not throw an exception. `U*` shall be implicitly convertible to `T*`. [Note: These requirements imply that `T` and `U` be complete types. -- end note]

   [ N.B.: The current wording of p. 6 already implicitly guarantees that `U` is completely defined, because it requires that `Convertible<U*, T*>` is true, see (6)+(8). ]

10. 20.8.14.2.3 [unique.ptr.single.asgn]/11: No changes necessary.

    [ N.B.: Delegation to requirements of effects clause is sufficient. ]

11. 20.8.14.2.4 [unique.ptr.single.observers]/1+4+7+9+11:

>     T* operator->() const;

> > Note: Use typically requires `T` shall be complete. -- end note]

12. 20.8.14.2.5 [unique.ptr.single.modifiers]/1: No changes necessary.

13. 20.8.14.2.5 [unique.ptr.single.modifiers]/4: Just before p. 4 add a new paragraph:

    > Requires: The expression `get_deleter()(get())` shall be well-formed, shall have well-defined behavior, and shall not throw exceptions.

14. 20.8.14.2.5 [unique.ptr.single.modifiers]/7: No changes necessary.

15. 20.8.14.3 [unique.ptr.runtime]: Add one additional bullet on paragraph 1:

    > A specialization for array types is provided with a slightly altered interface.

    > - ...
    > - `T` shall be a complete type.

[ post Bellevue: Daniel provided revised wording. ]

### 765. more on iterator validity

Section: X [iterator.concepts] Status: WP Submitter: Martin Sebor Opened: 2007-12-14 Last modified: 2009-07-18

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Discussion:

Issue 278 defines the meaning of the term "invalid iterator" as one that may be singular.

Consider the following code:

       std::deque<int> x, y;
       std::deque<int>::iterator i = x.end(), j = y.end();
       x.swap(y);

Given that `swap()` is required not to invalidate iterators and using the definition above, what should be the expected result of comparing `i` and `j` to `x.end()` and `y.end()`, respectively, after the `swap()`?

I.e., is the expression below required to evaluate to `true`?

       i == y.end() && j == x.end()

(There are at least two implementations where the expression returns `false`.)

More generally, is the definition introduced in issue 278 meant to make any guarantees about whether iterators actually point to the same elements or be associated with the same containers after a non-invalidating operation as they did before?

Here's a motivating example intended to demonstrate the importance of the question:

       Container x, y ({ 1, 2});   // pseudocode to initialize y with { 1, 2 }
       Container::iterator i = y.begin() + 1;
       Container::iterator j = y.end();
       std::swap(x, y);
       std::find(i, j, 3);

`swap()` guarantees that `i` and `j` continue to be valid. Unless the spec says that even though they are valid they may no longer denote a valid range the code above must be well-defined. Expert opinions on this differ as does the behavior of popular implementations for some standard `Containers`.

[ San Francisco: ]

> Pablo: add a note to the last bullet of paragraph 11 of 23.1.1 clarifying that the end() iterator doesn't refer to an element and that it can therefore be invalidated.

> Proposed wording:

> > [Note: The `end()` iterator does not refer to any element and can therefore be invalidated. -- end note]

> Howard will add this proposed wording to the issue and then move it to Review.

[ Post Summit: ]

> Lawrence: suggestion: "Note: The `end()` iterator does not refer to any element"

> Walter: "Note: The `end()` iterator can nevertheless be invalidated, because it does not refer to any element."

> Nick: "The `end()` iterator does not refer to any element. It is therefore subject to being invalidated."

> Consensus: go with Nick

> With that update, Recommend Tentatively Ready.

Proposed resolution:

Add to 23.2.1 [container.requirements.general], p11:

> Unless otherwise specified (see 23.1.4.1, 23.1.5.1, 23.2.2.3, and 23.2.6.4) all container types defined in this Clause meet the following additional requirements:

> - ...
> - no `swap()` function invalidates any references, pointers, or iterators referring to the elements of the containers being swapped. [Note: The `end()` iterator does not refer to any element. It is therefore subject to being invalidated. -- end note]

### 766. Inconsistent exception guarantees between ordered and unordered associative containers

Section: 23.2 [container.requirements], 23.2.5.1 [unord.req.except] Status: CD1 Submitter: Ion Gaztañaga Opened: 2007-12-22 Last modified: 2008-09-26

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Discussion:

23.2 [container.requirements]p10 states:

> Unless otherwise specified (see 23.2.2.3 and 23.2.5.4) all container types defined in this clause meet the following additional requirements:

> - [...]
> - no `erase()`, `pop_back()` or `pop_front()` function throws an exception.

23.3.2.3 [deque.modifiers] and 23.3.6.4 [vector.modifiers] offer additional guarantees for `deque`/`vector insert()` and `erase()` members. However, 23.2 [container.requirements]p10 does not mention 23.2.5.1 [unord.req.except] that specifies exception safety guarantees for unordered containers. In addition, 23.2.5.1 [unord.req.except]p1 offers the following guaratee for `erase()`:

> No `erase()` function throws an exception unless that exception is thrown by the container's Hash or Pred object (if any).

Summary:

According to 23.2 [container.requirements]p10 no `erase()` function should throw an exception unless otherwise specified. Although does not explicitly mention 23.2.5.1 [unord.req.except], this section offers additional guarantees for unordered containers, allowing `erase()` to throw if predicate or hash function throws.

In contrast, associative containers have no exception safety guarantees section so no `erase()` function should throw, including `erase(k)` that needs to use the predicate function to perform its work. This means that the predicate of an associative container is not allowed to throw.

So:

1. `erase(k)` for associative containers is not allowed to throw. On the other hand, `erase(k)` for unordered associative containers is allowed to throw.
2. `erase(q)` for associative containers is not allowed to throw. On the other hand, `erase(q)` for unordered associative containers is allowed to throw if it uses the hash or predicate.
3. To fulfill 1), predicates of associative containers are not allowed to throw. Predicates of unordered associative containers are allowed to throw.
4. 2) breaks a widely used programming pattern (flyweight pattern) for unordered containers, where objects are registered in a global map in their constructors and unregistered in their destructors. If `erase(q)` is allowed to throw, the destructor of the object would need to rethrow the exception or swallow it, leaving the object registered.

Proposed resolution:

Create a new sub-section of 23.2.4 [associative.reqmts] (perhaps [associative.req.except]) titled "Exception safety guarantees".

> 1 For associative containers, no `clear()` function throws an exception. `erase(k)` does not throw an exception unless that exception is thrown by the container's Pred object (if any).

> 2 For associative containers, if an exception is thrown by any operation from within an `insert()` function inserting a single element, the `insert()` function has no effect.

> 3 For associative containers, no `swap` function throws an exception unless that exception is thrown by the copy constructor or copy assignment operator of the container's Pred object (if any).

Change 23.2.5.1 [unord.req.except]p1:

> For unordered associative containers, no `clear()` function throws an exception. No `erase(k)` function does not throws an exception unless that exception is thrown by the container's Hash or Pred object (if any).

Change 23.2 [container.requirements]p10 to add references to new sections:

> Unless otherwise specified (see [deque.modifiers], and [vector.modifiers], [associative.req.except], [unord.req.except]) all container types defined in this clause meet the following additional requirements:

Change 23.2 [container.requirements]p10 referring to `swap`:

> - no `swap()` function throws an exception unless that exception is thrown by the copy constructor or assignment operator of the container's Compare object (if any; see [associative.reqmts]).

### 768. Typos in [atomics]?

Section: 29.5.3 [atomics.types.generic] Status: CD1 Submitter: Alberto Ganesh Barbati Opened: 2007-12-28 Last modified: 2008-09-26

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Discussion:

in the latest publicly available draft, paper N2641, in section 29.5.3 [atomics.types.generic], the following specialization of the template `atomic<>` is provided for pointers:

>     template <class T> struct atomic<T*> : atomic_address {
>       T* fetch_add(ptrdiff_t, memory_order = memory_order_seq_cst) volatile;
>       T* fetch_sub(ptrdiff_t, memory_order = memory_order_seq_cst) volatile;

>       atomic() = default;
>       constexpr explicit atomic(T);
>       atomic(const atomic&) = delete;
>       atomic& operator=(const atomic&) = delete;

>       T* operator=(T*) volatile;
>       T* operator++(int) volatile;
>       T* operator--(int) volatile;
>       T* operator++() volatile;
>       T* operator--() volatile;
>       T* operator+=(ptrdiff_t) volatile;
>       T* operator-=(ptrdiff_t) volatile;
>     };

First of all, there is a typo in the non-default constructor which should take a `T*` rather than a `T`.

As you can see, the specialization redefine and therefore hide a few methods from the base class `atomic_address`, namely `fetch_add`, `fetch_sub`, `operator=`, `operator+=` and `operator-=`. That's good, but... what happened to the other methods, in particular these ones:

>     void store(T*, memory_order = memory_order_seq_cst) volatile;
>     T* load( memory_order = memory_order_seq_cst ) volatile;
>     T* swap( T*, memory_order = memory_order_seq_cst ) volatile;
>     bool compare_swap( T*&, T*, memory_order, memory_order ) volatile;
>     bool compare_swap( T*&, T*, memory_order = memory_order_seq_cst ) volatile;

By reading paper N2427 "C++ Atomic Types and Operations", I see that the definition of the specialization `atomic<T*>` matches the one in the draft, but in the example implementation the methods `load()`, `swap()` and `compare_swap()` are indeed present.

Strangely, the example implementation does not redefine the method `store()`. It's true that a `T*` is always convertible to `void*`, but not hiding the `void*` signature from the base class makes the class error-prone to say the least: it lets you assign pointers of any type to a `T*`, without any hint from the compiler.

Is there a true intent to remove them from the specialization or are they just missing from the definition because of a mistake?

[ Bellevue: ]

> The proposed revisions are accepted.

> Further discussion: why is the ctor labeled "constexpr"? Lawrence said this permits the object to be statically initialized, and that's important because otherwise there would be a race condition on initialization.

Proposed resolution:

Change the synopsis in 29.5.3 [atomics.types.generic]:

>     template <class T> struct atomic<T*> : atomic_address {
>       void store(T*, memory_order = memory_order_seq_cst) volatile;
>       T* load( memory_order = memory_order_seq_cst ) volatile;
>       T* swap( T*, memory_order = memory_order_seq_cst ) volatile;
>       bool compare_swap( T*&, T*, memory_order, memory_order ) volatile;
>       bool compare_swap( T*&, T*, memory_order = memory_order_seq_cst ) volatile;

>       T* fetch_add(ptrdiff_t, memory_order = memory_order_seq_cst) volatile;
>       T* fetch_sub(ptrdiff_t, memory_order = memory_order_seq_cst) volatile;

>       atomic() = default;
>       constexpr explicit atomic(T*);
>       atomic(const atomic&) = delete;
>       atomic& operator=(const atomic&) = delete;

>       T* operator=(T*) volatile;
>       T* operator++(int) volatile;
>       T* operator--(int) volatile;
>       T* operator++() volatile;
>       T* operator--() volatile;
>       T* operator+=(ptrdiff_t) volatile;
>       T* operator-=(ptrdiff_t) volatile;
>     };

### 769. std::function should use nullptr_t instead of "unspecified-null-pointer-type"

Section: 20.7.15.2 [func.wrap.func] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-10 Last modified: 2008-09-26

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Discussion:

N2461 already replaced in 20.7.15.2 [func.wrap.func] it's originally proposed (implicit) conversion operator to "unspecified-bool-type" by the new explicit bool conversion, but the inverse conversion should also use the new `std::nullptr_t` type instead of "unspecified-null-pointer- type".

Proposed resolution:

In 20.7 [function.objects], header `<functional>` synopsis replace:

>     template<class R, class... ArgTypes>
>       bool operator==(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
>     template<class R, class... ArgTypes>
>       bool operator==(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);
>     template<class R, class... ArgTypes>
>       bool operator!=(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
>     template<class R, class... ArgTypes>
>       bool operator!=(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);

In the class function synopsis of 20.7.15.2 [func.wrap.func] replace

>     function(unspecified-null-pointer-type nullptr_t);
>     ...
>     function& operator=(unspecified-null-pointer-type nullptr_t);

In 20.7.15.2 [func.wrap.func], "Null pointer comparisons" replace:

>     template <class R, class... ArgTypes>
>       bool operator==(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
>     template <class R, class... ArgTypes>
>       bool operator==(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);
>     template <class R, class... ArgTypes>
>       bool operator!=(const function<R(ArgTypes...)>&, unspecified-null-pointer-type nullptr_t);
>     template <class R, class... ArgTypes>
>       bool operator!=(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>&);

In 20.7.15.2.1 [func.wrap.func.con], replace

>     function(unspecified-null-pointer-type nullptr_t);
>     ...
>     function& operator=(unspecified-null-pointer-type nullptr_t);

In 20.7.15.2.6 [func.wrap.func.nullptr], replace

>     template <class R, class... ArgTypes>
>       bool operator==(const function<R(ArgTypes...)>& f, unspecified-null-pointer-type nullptr_t);
>     template <class R, class... ArgTypes>
>       bool operator==(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>& f);

and replace

>     template <class R, class... ArgTypes>
>       bool operator!=(const function<R(ArgTypes...)>& f, unspecified-null-pointer-type nullptr_t);
>     template <class R, class... ArgTypes>
>       bool operator!=(unspecified-null-pointer-type nullptr_t , const function<R(ArgTypes...)>& f);

### 770. std::function should use rvalue swap

Section: 20.7.15 [func.wrap] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-10 Last modified: 2008-09-26

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Discussion:

It is expected that typical implementations of `std::function` will use dynamic memory allocations at least under given conditions, so it seems appropriate to change the current lvalue swappabilty of this class to rvalue swappability.

Proposed resolution:

In 20.7 [function.objects], header `<functional>` synopsis, just below of

>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);

In 20.7.15.2 [func.wrap.func] class `function` definition, change

>     void swap(function&&);

In 20.7.15.2 [func.wrap.func], just below of

>     template <class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&);
>     template <class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&);
>     template <class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);

In 20.7.15.2.2 [func.wrap.func.mod] change

>     void swap(function&& other);

In 20.7.15.2.7 [func.wrap.func.alg] add the two overloads

>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>&& f1, function<R(ArgTypes...)>& f2);
>     template<class R, class... ArgTypes>
>       void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>&& f2);

### 771. Impossible throws clause in [string.conversions]

Section: 21.5 [string.conversions] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-13 Last modified: 2008-09-26

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Discussion:

The new `to_string` and `to_wstring` functions described in 21.5 [string.conversions] have throws clauses (paragraphs 8 and 16) which say:

> Throws: nothing

Since all overloads return either a `std::string` or a `std::wstring` by value this throws clause is impossible to realize in general, since the `basic_string` constructors can fail due to out-of-memory conditions. Either these throws clauses should be removed or should be more detailled like:

> Throws: Nothing if the string construction throws nothing

Further there is an editorial issue in p. 14: All three `to_wstring` overloads return a `string`, which should be `wstring` instead (The header `<string>` synopsis of 21.3 [string.classes] is correct in this regard).

Proposed resolution:

In 21.5 [string.conversions], remove the paragraphs 8 and 16.

>     string to_string(long long val);
>     string to_string(unsigned long long val);
>     string to_string(long double val);

> > Throws: nothing

>     wstring to_wstring(long long val);
>     wstring to_wstring(unsigned long long val);
>     wstring to_wstring(long double val);

> > Throws: nothing

### 772. Impossible return clause in [string.conversions]

Section: 21.5 [string.conversions] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-13 Last modified: 2008-09-26

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Discussion:

The return clause 21.5 [string.conversions]/paragraph 15 of the new `to_wstring` overloads says:

> Returns: each function returns a `wstring` object holding the character representation of the value of its argument that would be generated by calling `wsprintf(buf, fmt, val)` with a format specifier of `L"%lld"`, `L"%ulld"`, or `L"%f"`, respectively.

Problem is: There does not exist any `wsprintf` function in C99 (I checked the 2nd edition of ISO 9899, and the first and the second corrigenda from 2001-09-01 and 2004-11-15). What probably meant here is the function `swprintf` from `<wchar.h>/<cwchar>`, but this has the non-equivalent declaration:

>     int swprintf(wchar_t * restrict s, size_t n,
>     const wchar_t * restrict format, ...);

therefore the paragraph needs to mention the `size_t` parameter `n`.

Proposed resolution:

Change the current wording of 21.5 [string.conversions]/p. 15 to:

> Returns: e Each function returns a `wstring` object holding the character representation of the value of its argument that would be generated by calling `wsswprintf(buf, bufsz, fmt, val)` with a format specifier `fmt` of `L"%lld"`, `L"%ulld"`, or `L"%f"`, respectively, where `buf` designates an internal character buffer of sufficient size `bufsz`.

[Hint to the editor: The resolution also adds to mention the name of the format specifier "fmt"]

I also would like to remark that the current wording of it's equivalent paragraph 7 should also mention the meaning of `buf` and `fmt`.

Change the current wording of 21.5 [string.conversions]/p. 7 to:

> Returns: e Each function returns a string object holding the character representation of the value of its argument that would be generated by calling `sprintf(buf, fmt, val)` with a format specifier `fmt` of `"%lld"`, `"%ulld"`, or `"%f"`, respectively, where `buf` designates an internal character buffer of sufficient size.

### 775. Tuple indexing should be unsigned?

Section: 20.5.2.5 [tuple.helper] Status: CD1 Submitter: Alisdair Meredith Opened: 2008-01-16 Last modified: 2008-09-26

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Discussion:

The tuple element access API identifies the element in the sequence using signed integers, and then goes on to enforce the requirement that I be >= 0. There is a much easier way to do this - declare I as `unsigned`.

In fact the proposal is to use `std::size_t`, matching the type used in the `tuple_size` API.

A second suggestion is that it is hard to imagine an API that deduces and index at compile time and returns a reference throwing an exception. Add a specific Throws: Nothing paragraph to each element access API.

In addition to `tuple`, update the API applies to `pair` and `array`, and should be updated accordingly.

A third observation is that the return type of the `get` functions for `std::pair` is pseudo-code, but it is not clearly marked as such. There is actually no need for pseudo-code as the return type can be specified precisely with a call to `tuple_element`. This is already done for `std::tuple`, and `std::array` does not have a problem as all elements are of type `T`.

Proposed resolution:

Update header <utility> synopsis in 20.3 [utility]

    // 20.2.3, tuple-like access to pair:
    template <class T> class tuple_size;
    template <intsize_t I, class T> class tuple_element;

    template <class T1, class T2> struct tuple_size<std::pair<T1, T2> >;
    template <class T1, class T2> struct tuple_element<0, std::pair<T1, T2> >;
    template <class T1, class T2> struct tuple_element<1, std::pair<T1, T2> >;

    template<intsize_t I, class T1, class T2>
      Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(std::pair<T1, T2>&);
    template<intsize_t I, class T1, class T2>
      const Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(const std::pair<T1, T2>&);

Update 20.3.4 [pairs] Pairs

    template<intsize_t I, class T1, class T2>
      Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(pair<T1, T2>&);
    template<intsize_t I, class T1, class T2>
      const Ptypename tuple_element<I, std::pair<T1, T2> >::type & get(const pair<T1, T2>&);

24 Return type: If `I == 0` then `P` is `T1`, if `I == 1` then `P` is `T2`, and otherwise the program is ill-formed.

25 Returns: If `I == 0` returns `p.first`, otherwise if `I == 1` returns `p.second`, and otherwise the program is ill-formed.

Throws: Nothing.

Update header <tuple> synopsis in 20.5 [tuple] with a APIs as below:

    template <intsize_t I, class T> class tuple_element; // undefined
    template <intsize_t I, class... Types> class tuple_element<I, tuple<Types...> >;

    // 20.3.1.4, element access:
    template <intsize_t I, class... Types>
      typename tuple_element<I, tuple<Types...> >::type& get(tuple<Types...>&);
    template <intsize_t I, class ... types>
      typename tuple_element<I, tuple<Types...> >::type const& get(const tuple<Types...>&);

Update 20.5.2.5 [tuple.helper] Tuple helper classes

    template <intsize_t I, class... Types>
    class tuple_element<I, tuple<Types...> > {
    public:
      typedef TI type;
    };

1 Requires: `0 <= I and I < sizeof...(Types)`. The program is ill-formed if `I` is out of bounds.

2 Type: `TI` is the type of the `I`th element of `Types`, where indexing is zero-based.

Update 20.5.2.6 [tuple.elem] Element access

    template <intsize_t I, class... types >
    typename tuple_element<I, tuple<Types...> >::type& get(tuple<Types...>& t);

1 Requires: `0 <= I and I < sizeof...(Types)`. The program is ill-formed if `I` is out of bounds.

2 Returns: A reference to the `I`th element of `t`, where indexing is zero-based.

Throws: Nothing.

    template <intsize_t I, class... types>
    typename tuple_element<I, tuple<Types...> >::type const& get(const tuple<Types...>& t);

3 Requires: `0 <= I and I < sizeof...(Types)`. The program is ill-formed if `I` is out of bounds.

4 Returns: A const reference to the `I`th element of `t`, where indexing is zero-based.

Throws: Nothing.

Update header <array> synopsis in 20.3 [utility]

    template <class T> class tuple_size; // forward declaration
    template <intsize_t I, class T> class tuple_element; // forward declaration
    template <class T, size_t N>
      struct tuple_size<array<T, N> >;
    template <intsize_t I, class T, size_t N>
      struct tuple_element<I, array<T, N> >;
    template <intsize_t I, class T, size_t N>
      T& get(array<T, N>&);
    template <intsize_t I, class T, size_t N>
      const T& get(const array<T, N>&);

Update 23.3.1.7 [array.tuple] Tuple interface to class template array

    tuple_element<size_t I, array<T, N> >::type

3 Requires: `0 <= I < N.` The program is ill-formed if `I` is out of bounds.

4 Value: The type `T`.

    template <intsize_t I, class T, size_t N> T& get(array<T, N>& a);

5 Requires: `0 <= I < N`. The program is ill-formed if `I` is out of bounds.

Returns: A reference to the `I`th element of `a`, where indexing is zero-based.

Throws: Nothing.

    template <intsize_t I, class T, size_t N> const T& get(const array<T, N>& a);

6 Requires: `0 <= I < N`. The program is ill-formed if `I` is out of bounds.

7 Returns: A const reference to the `I`th element of `a`, where indexing is zero-based.

Throws: Nothing.

[ Bellevue: Note also that the phrase "The program is ill-formed if I is out of bounds" in the requires clauses are probably unnecessary, and could be removed at the editor's discretion. Also std:: qualification for pair is also unnecessary. ]

### 776. Undescribed assign function of std::array

Section: 23.3.1 [array] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-20 Last modified: 2008-09-26

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Discussion:

The class template array synopsis in 23.3.1 [array]/3 declares a member function

>     void assign(const T& u);

which's semantic is no-where described. Since this signature is not part of the container requirements, such a semantic cannot be derived by those.

I found only one reference to this function in the issue list, 588 where the question is raised:

> what's the effect of calling `assign(T&)` on a zero-sized array?

which does not answer the basic question of this issue.

If this function shall be part of the `std::array`, it's probable semantic should correspond to that of `boost::array`, but of course such wording must be added.

Proposed resolution:

Just after the section 23.3.1.4 [array.data] add the following new section:

23.2.1.5 array::fill [array.fill]

>     void fill(const T& u);

> 1: Effects: `fill_n(begin(), N, u)`

[N.B: I wonder, why class `array` does not have a "modifiers" section. If it had, then `assign` would naturally belong to it]

Change the synopsis in 23.3.1 [array]/3:

>     template <class T, size_t N>
>     struct array {
>       ...
>       void assign fill(const T& u);
>       ...

[ Bellevue: ]

> Suggest substituting "fill" instead of "assign".

> Set state to Review given substitution of "fill" for "assign".

### 777. Atomics Library Issue

Section: 29.6 [atomics.types.operations] Status: CD1 Submitter: Lawrence Crowl Opened: 2008-01-21 Last modified: 2008-09-26

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Discussion:

The load functions are defined as

>     C atomic_load(volatile A* object);
>     C atomic_load_explicit(volatile A* object, memory_order);
>     C A::load(memory_order order = memory_order_seq_cst) volatile;

which prevents their use in `const` contexts.

[ post Bellevue Peter adds: ]

> Issue 777 suggests making `atomic_load` operate on `const` objects. There is a subtle point here. Atomic loads do not generally write to the object, except potentially for the `memory_order_seq_cst` constraint. Depending on the architecture, a dummy write with the same value may be required to be issued by the atomic load to maintain sequential consistency. This, in turn, may make the following code:

> >     const atomic_int x{};

> >     int main()
> >     {
> >       x.load();
> >     }

> dump core under a straightforward implementation that puts const objects in a read-only section.

> There are ways to sidestep the problem, but it needs to be considered.

> The tradeoff is between making the data member of the atomic types mutable and requiring the user to explicitly mark atomic members as mutable, as is already the case with mutexes.

Proposed resolution:

Add the `const` qualifier to `*object` and `*this`.

>     C atomic_load(const volatile A* object);
>     C atomic_load_explicit(const volatile A* object, memory_order);
>     C A::load(memory_order order = memory_order_seq_cst) const volatile;

### 778. std::bitset does not have any constructor taking a string literal

Section: 20.3.7.1 [bitset.cons] Status: CD1 Submitter: Thorsten Ottosen Opened: 2008-01-24 Last modified: 2008-09-26

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Duplicate of: 116

Discussion:

A small issue with `std::bitset`: it does not have any constructor taking a string literal, which is clumsy and looks like an oversigt when we tried to enable uniform use of `string` and `const char*` in the library.

Suggestion: Add

>     explicit bitset( const char* str );

to std::bitset.

Proposed resolution:

Add to synopsis in 20.3.7 [template.bitset]

>     explicit bitset( const char* str );

Add to synopsis in 20.3.7.1 [bitset.cons]

>     explicit bitset( const char* str );

> Effects: Constructs a `bitset` as if `bitset(string(str))`.

### 779. Resolution of #283 incomplete

Section: 25.3.8 [alg.remove] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-25 Last modified: 2008-09-26

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Discussion:

The resolution of 283 did not resolve similar necessary changes for algorithm `remove_copy[_if]`, which seems to be an oversight.

Proposed resolution:

In 25.3.8 [alg.remove]/p.6, replace the N2461 requires clause with:

> Requires: Type `T` is `EqualityComparable` (31). The ranges `[first,last)` and `[result,result + (last - first))` shall not overlap. The expression `*result = *first` shall be valid.

### 781. `std::complex` should add missing C99 functions

Section: 26.4.7 [complex.value.ops] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-26 Last modified: 2009-03-21

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Discussion:

A comparision of the N2461 header `<complex>` synopsis ([complex.syn]) with the C99 standard (ISO 9899, 2nd edition and the two corrigenda) show some complex functions that are missing in C++. These are:

1. 7.3.9.4: (required elements of the C99 library)
   The `cproj` functions
2. 7.26.1: (optional elements of the C99 library)

       cerf    cerfc    cexp2
       cexpm1  clog10   clog1p
       clog2   clgamma  ctgamma

I propose that at least the required `cproj` overloads are provided as equivalent C++ functions. This addition is easy to do in one sentence (delegation to C99 function).

Please note also that the current entry `polar` in 26.4.9 [cmplx.over]/1 should be removed from the mentioned overload list. It does not make sense to require that a function already expecting scalar arguments should cast these arguments into corresponding `complex<T>` arguments, which are not accepted by this function.

Proposed resolution:

In 26.4.1 [complex.syn] add just between the declaration of `conj` and `fabs`:

>     template<class T> complex<T> conj(const complex<T>&);
>     template<class T> complex<T> proj(const complex<T>&);
>     template<class T> complex<T> fabs(const complex<T>&);

In 26.4.7 [complex.value.ops] just after p.6 (return clause of `conj`) add:

>     template<class T> complex<T> proj(const complex<T>& x);

> > Effects: Behaves the same as C99 function `cproj`, defined in subclause 7.3.9.4."

In 26.4.9 [cmplx.over]/1, add one further entry `proj` to the overload list.

> The following function templates shall have additional overloads:

> >     arg           norm
> >     conj          polar proj
> >     imag          real

### 782. Extended `seed_seq` constructor is useless

Section: 26.5.7.1 [rand.util.seedseq] Status: CD1 Submitter: Daniel Krügler Opened: 2008-01-27 Last modified: 2009-05-01

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Discussion:

Part of the resolution of n2423, issue 8 was the proposal to extend the `seed_seq` constructor accepting an input range as follows (which is now part of N2461):

>     template<class InputIterator,
>     size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits>
>     seed_seq(InputIterator begin, InputIterator end);

First, the expression `iterator_traits<InputIterator>::value_type` is invalid due to missing `typename` keyword, which is easy to fix.

Second (and worse), while the language now supports default template arguments of function templates, this customization point via the second `size_t` template parameter is of no advantage, because `u` can never be deduced, and worse - because it is a constructor function template - it can also never be explicitly provided (14.9.1 [temp.arg.explicit]/7).

The question arises, which advantages result from a compile-time knowledge of `u` versus a run time knowledge? If run time knowledge suffices, this parameter should be provided as normal function default argument [Resolution marked (A)], if compile-time knowledge is important, this could be done via a tagging template or more user-friendly via a standardized helper generator function (`make_seed_seq`), which allows this [Resolution marked (B)].

[ Bellevue: ]

> Fermilab does not have a strong opinion. Would prefer to go with solution A. Bill agrees that solution A is a lot simpler and does the job.

> Proposed Resolution: Accept Solution A.

Issue 803 claims to make this issue moot.

Proposed resolution:

1. In 26.5.7.1 [rand.util.seedseq]/2, class `seed_seq` synopsis replace:

   >     class seed_seq
   >     {
   >     public:
   >        ...
   >        template<class InputIterator,
   >           size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits>
   >               seed_seq(InputIterator begin, InputIterator end,
   >               size_t u = numeric_limits<typename iterator_traits<InputIterator>::value_type>::digits);
   >        ...
   >     };

   and do a similar replacement in the member description between p.3 and p.4.

2. In 26.5.7.1 [rand.util.seedseq]/2, class `seed_seq` synopsis and in the member description between p.3 and p.4 replace:

   >     template<class InputIterator,
   >       size_t u = numeric_limits<iterator_traits<InputIterator>::value_type>::digits>
   >           seed_seq(InputIterator begin, InputIterator end);
   >     template<class InputIterator, size_t u>
   >     seed_seq(InputIterator begin, InputIterator end, implementation-defined s);

   In 26.5.1 [rand.synopsis], header `<random>` synopsis, immediately after the class `seed_seq` declaration and in 26.5.7.1 [rand.util.seedseq]/2, immediately after the class `seed_seq` definition add:

   >     template<size_t u, class InputIterator>
   >       seed_seq make_seed_seq(InputIterator begin, InputIterator end);

   In 26.5.7.1 [rand.util.seedseq], just before p.5 insert two paragraphs:

   > The first constructor behaves as if it would provide an integral constant expression `u` of type `size_t` of value `numeric_limits<typename iterator_traits<InputIterator>::value_type>::digits`.

   > The second constructor uses an implementation-defined mechanism to provide an integral constant expression `u` of type `size_t` and is called by the function `make_seed_seq`.

   In 26.5.7.1 [rand.util.seedseq], just after the last paragraph add:

   >     template<size_t u, class InputIterator>
   >        seed_seq make_seed_seq(InputIterator begin, InputIterator end);

   > > where `u` is used to construct an object `s` of implementation-defined type.

   > > Returns: `seed_seq(begin, end, s)`;

### 783. `thread::id` reuse

Section: 30.3.1.1 [thread.thread.id] Status: CD1 Submitter: Hans Boehm Opened: 2008-02-01 Last modified: 2008-09-26

View all other issues in [thread.thread.id].

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Discussion:

The current working paper (N2497, integrated just before Bellevue) is not completely clear whether a given `thread::id` value may be reused once a thread has exited and has been joined or detached. Posix allows thread ids (`pthread_t` values) to be reused in this case. Although it is not completely clear whether this originally was the right decision, it is clearly the established practice, and we believe it was always the intent of the C++ threads API to follow Posix and allow this. Howard Hinnant's example implementation implicitly relies on allowing reuse of ids, since it uses Posix thread ids directly.

It is important to be clear on this point, since it the reuse of thread ids often requires extra care in client code, which would not be necessary if thread ids were unique across all time. For example, a hash table indexed by thread id may have to be careful not to associate data values from an old thread with a new one that happens to reuse the id. Simply removing the old entry after joining a thread may not be sufficient, if it creates a visible window between the join and removal during which a new thread with the same id could have been created and added to the table.

[ post Bellevue Peter adds: ]

> There is a real issue with `thread::id` reuse, but I urge the LWG to reconsider fixing this by disallowing reuse, rather than explicitly allowing it. Dealing with thread id reuse is an incredibly painful exercise that would just force the world to reimplement a non-conflicting `thread::id` over and over.

> In addition, it would be nice if a `thread::id` could be manipulated atomically in a lock-free manner, as motivated by the recursive lock example:

> http://www.decadentplace.org.uk/pipermail/cpp-threads/2006-August/001091.html

Proposed resolution:

Add a sentence to 30.3.1.1 [thread.thread.id]/p1:

> An object of type `thread::id` provides a unique identifier for each thread of execution and a single distinct value for all thread objects that do not represent a thread of execution ([thread.threads.class]). Each thread of execution has a `thread::id` that is not equal to the `thread::id` of other threads of execution and that is not equal to the `thread::id` of `std::thread` objects that do not represent threads of execution. The library may reuse the value of a `thread::id` of a terminated thread that can no longer be joined.

### 787. complexity of `binary_search`

Section: 25.4.3.4 [binary.search] Status: CD1 Submitter: Daniel Krügler Opened: 2007-09-08 Last modified: 2008-09-26

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Discussion:

In 25.4.3.4 [binary.search]/3 the complexity of `binary_search` is described as

> At most `log(last - first) + 2` comparisons.

This should be precised and brought in line with the nomenclature used for `lower_bound`, `upper_bound`, and `equal_range`.

All existing libraries I'm aware of, delegate to `lower_bound` (+ one further comparison). Since issue 384 has now WP status, the resolution of #787 should be brought in-line with 384 by changing the `+ 2` to `+ O(1)`.

[ Sophia Antipolis: ]

> Alisdair prefers to apply an upper bound instead of O(1), but that would require fixing for `lower_bound`, `upper_bound` etc. as well. If he really cares about it, he'll send an issue to Howard.

Proposed resolution:

Change 25.4.3.4 [binary.search]/3

> Complexity: At most `log2(last - first) + 2 O(1)` comparisons.

### 788. ambiguity in [istream.iterator]

Section: 24.6.1 [istream.iterator] Status: WP Submitter: Martin Sebor Opened: 2008-02-06 Last modified: 2009-10-26

View all other issues in [istream.iterator].

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Discussion:

Addresses UK 287

> It is not clear what the initial state of an `istream_iterator` should be. Is _value_ initialized by reading the stream, or default/value initialized? If it is initialized by reading the stream, what happens if the initialization is deferred until first dereference, when ideally the iterator value should have been that of an end-of-stream iterator which is not safely dereferencable?

> Recommendation: Specify _value_ is initialized by reading the stream, or the iterator takes on the end-of-stream value if the stream is empty.

The description of how an istream_iterator object becomes an end-of-stream iterator is a) ambiguous and b) out of date WRT issue 468:

> `istream_iterator` reads (using `operator>>`) successive elements from the input stream for which it was constructed. After it is constructed, and every time `++` is used, the iterator reads and stores a value of `T`. If the end of stream is reached (`operator void*()` on the stream returns `false`), the iterator becomes equal to the end-of-stream iterator value. The constructor with no arguments `istream_iterator()` always constructs an end of stream input iterator object, which is the only legitimate iterator to be used for the end condition. The result of `operator*` on an end of stream is not defined. For any other iterator value a `const T&` is returned. The result of `operator->` on an end of stream is not defined. For any other iterator value a `const T*` is returned. It is impossible to store things into istream iterators. The main peculiarity of the istream iterators is the fact that `++` operators are not equality preserving, that is, `i == j` does not guarantee at all that `++i == ++j`. Every time `++` is used a new value is read.

`istream::operator void*()` returns null if `istream::fail()` is `true`, otherwise non-null. `istream::fail()` returns `true` if `failbit` or `badbit` is set in `rdstate()`. Reaching the end of stream doesn't necessarily imply that `failbit` or `badbit` is set (e.g., after extracting an `int` from `stringstream("123")` the stream object will have reached the end of stream but `fail()` is `false` and `operator void*()` will return a non-null value).

Also I would prefer to be explicit about calling `fail()` here (there is no `operator void*()` anymore.)

[ Summit: ]

> Moved from Ready to Open for the purposes of using this issue to address NB UK 287. Martin to handle.

[ 2009-07 Frankfurt: ]

> This improves the wording.

> Move to Ready.

Proposed resolution:

Change 24.6.1 [istream.iterator]/1:

> `istream_iterator` reads (using `operator>>`) successive elements from the input stream for which it was constructed. After it is constructed, and every time `++` is used, the iterator reads and stores a value of `T`. If the end of stream is reached the iterator fails to read and store a value of `T` (`operator void*() fail()` on the stream returns `false true`), the iterator becomes equal to the end-of-stream iterator value. The constructor with no arguments `istream_iterator()` always constructs an end of stream input iterator object, which is the only legitimate iterator to be used for the end condition. The result of `operator*` on an end of stream is not defined. For any other iterator value a `const T&` is returned. The result of `operator->` on an end of stream is not defined. For any other iterator value a `const T*` is returned. It is impossible to store things into istream iterators. The main peculiarity of the istream iterators is the fact that `++` operators are not equality preserving, that is, `i == j` does not guarantee at all that `++i == ++j`. Every time `++` is used a new value is read.

### 789. `xor_combine_engine(result_type)` should be explicit

Section: X [rand.adapt.xor] Status: CD1 Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2008-09-26

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Discussion:

`xor_combine_engine(result_type)` should be `explicit`. (Obvious oversight.)

[ Bellevue: ]

> Non-controversial. Bill is right, but Fermilab believes that this is easy to use badly and hard to use right, and so it should be removed entirely. Got into TR1 by well defined route, do we have permission to remove stuff? Should probably check with Jens, as it is believed he is the originator. Broad consensus that this is not a robust engine adapter.

Proposed resolution:

Remove xor_combine_engine from synopsis of 26.5.1 [rand.synopsis].

Remove X [rand.adapt.xor] `xor_combine_engine`.

### 792. `piecewise_constant_distribution` is undefined for a range with just one endpoint

Section: 26.5.8.5.2 [rand.dist.samp.pconst] Status: CD1 Submitter: P.J. Plauger Opened: 2008-02-09 Last modified: 2008-09-26

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Discussion:

`piecewise_constant_distribution` is undefined for a range with just one endpoint. (Probably should be the same as an empty range.)

Proposed resolution:

Change 26.5.8.5.2 [rand.dist.samp.pconst] paragraph 3b:

> b) If `firstB == lastB` or the sequence `w` has the length zero,

### 798. Refactoring of binders lead to interface breakage

Section: D.9 [depr.lib.binders] Status: CD1 Submitter: Daniel Krügler Opened: 2008-02-14 Last modified: 2008-09-26

View all other issues in [depr.lib.binders].

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Discussion:

N2521 and its earlier predecessors have moved the old binders from [lib.binders] to D.9 [depr.lib.binders] thereby introducing some renaming of the template parameter names (`Operation -> Fn`). During this renaming process the protected data member `op` was also renamed to `fn`, which seems as an unnecessary interface breakage to me - even if this user access point is probably rarely used.

Proposed resolution:

Change D.9.1 [depr.lib.binder.1st]:

>     template <class Fn>
>     class binder1st
>       : public unary_function<typename Fn::second_argument_type,
>                               typename Fn::result_type> {
>     protected:
>       Fn fn op;
>       typename Fn::first_argument_type value;
>     public:
>       binder1st(const Fn& x,
>                 const typename Fn::first_argument_type& y);
>       typename Fn::result_type
>         operator()(const typename Fn::second_argument_type& x) const;
>       typename Fn::result_type
>         operator()(typename Fn::second_argument_type& x) const;
>     };

> > -1- The constructor initializes `fn` `op` with `x` and `value` with `y`.

> > -2- `operator()` returns `fnop(value,x)`.

Change D.9.3 [depr.lib.binder.2nd]:

>     template <class Fn>
>     class binder2nd
>       : public unary_function<typename Fn::first_argument_type,
>                               typename Fn::result_type> {
>     protected:
>       Fn fn op;
>       typename Fn::second_argument_type value;
>     public:
>       binder2nd(const Fn& x,
>                 const typename Fn::second_argument_type& y);
>       typename Fn::result_type
>         operator()(const typename Fn::first_argument_type& x) const;
>       typename Fn::result_type
>         operator()(typename Fn::first_argument_type& x) const;
>     };

> > -1- The constructor initializes `fn` `op` with `x` and `value` with `y`.

> > -2- `operator()` returns `fnop(value,x)`.

### 804. Some problems with classes `error_code`/`error_condition`

Section: 19.5 [syserr] Status: CD1 Submitter: Daniel Krügler Opened: 2008-02-24 Last modified: 2008-09-26

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Discussion:

1. 19.5.2.1 [syserr.errcode.overview]/1, class `error_code` and 19.5.3.1 [syserr.errcondition.overview]/, class `error_condition` synopses declare an expository data member `cat_`:

   >     const error_category& cat_; // exposition only

   which is used to define the semantics of several members. The decision to use a member of reference type lead to several problems:

   1. The classes are not `(Copy)Assignable`, which is probably not the intent.
   2. The post conditions of all modifiers from 19.5.2.3 [syserr.errcode.modifiers] and 19.5.3.3 [syserr.errcondition.modifiers], resp., cannot be fulfilled.

   The simple fix would be to replace the reference by a pointer member.

2. I would like to give the editorial remark that in both classes the constrained `operator=` overload (template with `ErrorCodeEnum` argument) makes in invalid usage of `std::enable_if`: By using the default value for the second `enable_if` parameter the return type would be defined to be `void&` even in otherwise valid circumstances - this return type must be explicitly provided (In `error_condition` the first declaration uses an explicit value, but of wrong type).
3. The member function `message` throws clauses ( 19.5.1.2 [syserr.errcat.virtuals]/10, 19.5.2.4 [syserr.errcode.observers]/8, and 19.5.3.4 [syserr.errcondition.observers]/6) guarantee "throws nothing", although they return a `std::string` by value, which might throw in out-of-memory conditions (see related issue 771).

[ Sophia Antipolis: ]

> Part A: NAD (editorial), cleared by the resolution of issue 832.

> Part B: Technically correct, save for typo. Rendered moot by the concept proposal (N2620) NAD (editorial).

> Part C: We agree; this is consistent with the resolution of issue 721.

> Howard: please ping Beman, asking him to clear away parts A and B from the wording in the proposed resolution, so it is clear to the editor what needs to be applied to the working paper.

> Beman provided updated wording. Since issue 832 is not going forward, the provided wording includes resolution of part A.

Proposed resolution:

Resolution of part A:

> Change 19.5.2.1 [syserr.errcode.overview] Class error_code overview synopsis as indicated:

> >     private:
> >       int val_;                    // exposition only
> >       const error_category&* cat_; // exposition only

> Change 19.5.2.2 [syserr.errcode.constructors] Class error_code constructors as indicated:

> >     error_code();

> > > Effects: Constructs an object of type `error_code`.

> > > Postconditions: `val_ == 0` and `cat_ == &system_category`.

> > > Throws: Nothing.

> >     error_code(int val, const error_category& cat);

> > > Effects: Constructs an object of type `error_code`.

> > > Postconditions: `val_ == val` and `cat_ == &cat`.

> > > Throws: Nothing.

> Change 19.5.2.3 [syserr.errcode.modifiers] Class error_code modifiers as indicated:

> >     void assign(int val, const error_category& cat);

> > > Postconditions: `val_ == val` and `cat_ == &cat`.

> > > Throws: Nothing.

> Change 19.5.2.4 [syserr.errcode.observers] Class error_code observers as indicated:

> > const error_category& category() const;

> > > Returns: `*cat_`.

> > > Throws: Nothing.

> Change 19.5.3.1 [syserr.errcondition.overview] Class error_condition overview synopsis as indicated:

> >     private:
> >       int val_;                    // exposition only
> >       const error_category&* cat_; // exposition only

> Change 19.5.3.2 [syserr.errcondition.constructors] Class error_condition constructors as indicated:

> [ (If the proposed resolution of issue 805 has already been applied, the name `posix_category` will have been changed to `generic_category`. That has no effect on this resolution.) ]

> >     error_condition();

> > > Effects: Constructs an object of type `error_condition`.

> > > Postconditions: `val_ == 0` and `cat_ == &posix_category`.

> > > Throws: Nothing.

> >     error_condition(int val, const error_category& cat);

> > > Effects: Constructs an object of type `error_condition`.

> > > Postconditions: `val_ == val` and `cat_ == &cat`.

> > > Throws: Nothing.

> Change 19.5.3.3 [syserr.errcondition.modifiers] Class error_condition modifiers as indicated:

> > void assign(int val, const error_category& cat);

> > > Postconditions: `val_ == val` and `cat_ == &cat`.

> > > Throws: Nothing.

> Change 19.5.3.4 [syserr.errcondition.observers] Class error_condition observers as indicated:

> > const error_category& category() const;

> > > Returns: `*cat_`.

> > > Throws: Nothing.

Resolution of part C:

> In 19.5.1.2 [syserr.errcat.virtuals], remove the throws clause p. 10.

> >     virtual string message(int ev) const = 0;

> > > Returns: A string that describes the error condition denoted by `ev`.

> > > Throws: Nothing.

> In 19.5.2.4 [syserr.errcode.observers], remove the throws clause p. 8.

> >     string message() const;

> > > Returns: `category().message(value())`.

> > > Throws: Nothing.

> In 19.5.3.4 [syserr.errcondition.observers], remove the throws clause p. 6.

> >     string message() const;

> > > Returns: `category().message(value())`.

> > > Throws: Nothing.

### 805. `posix_error::posix_errno` concerns

Section: 19.5 [syserr] Status: CD1 Submitter: Jens Maurer Opened: 2008-02-24 Last modified: 2008-09-26

View all other issues in [syserr].

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Discussion:

19.5 [syserr]

>     namespace posix_error {
>       enum posix_errno {
>         address_family_not_supported, // EAFNOSUPPORT
>         ...

should rather use the new scoped-enum facility (7.2 [dcl.enum]), which would avoid the necessity for a new `posix_error` namespace, if I understand correctly.

[ Further discussion: ]

> See N2347, Strongly Typed Enums, since renamed Scoped Enums.

> Alberto Ganesh Barbati also raised this issue in private email, and also proposed the scoped-enum solution.

> Nick Stoughton asked in Bellevue that `posix_error` and `posix_errno` not be used as names. The LWG agreed.

> The wording for the Proposed resolution was provided by Beman Dawes.

Proposed resolution:

Change System error support 19.5 [syserr] as indicated:

>     namespace posix_error {
>       enum posix_errno class errc {
>         address_family_not_supported, // EAFNOSUPPORT
>         ...
>         wrong_protocol_type, // EPROTOTYPE
>       };
>     } // namespace posix_error

>     template <> struct is_error_condition_enum<posix_error::posix_errno errc>
>       : public true_type {}

>     namespace posix_error {
>       error_code make_error_code(posix_errno errc e);
>       error_condition make_error_condition(posix_errno errc e);
>     } // namespace posix_error

Change System error support 19.5 [syserr] :

> The `is_error_code_enum` and `is_error_condition_enum` templates may be specialized for user-defined types to indicate that such a type is eligible for class `error_code` and class `error_condition` automatic conversions, respectively.

Change System error support 19.5 [syserr] and its subsections:

> - remove all occurrences of `posix_error::`
> - change all instances of `posix_errno` to `errc`
> - change all instances of `posix_category` to `generic_category`
> - change all instances of `get_posix_category` to `get_generic_category`

Change Error category objects 19.5.1.5 [syserr.errcat.objects], paragraph 2:

> Remarks: The object's `default_error_condition` and equivalent virtual functions shall behave as specified for the class `error_category`. The object's name virtual function shall return a pointer to the string "POSIX" "generic".

Change 19.5.2.5 [syserr.errcode.nonmembers] Class `error_code` non-member functions as indicated:

>     error_code make_error_code(posix_errno errc e);

> > Returns: `error_code(static_cast<int>(e), posixgeneric_category)`.

Change 19.5.3.5 [syserr.errcondition.nonmembers] Class `error_condition` non-member functions as indicated:

>     error_condition make_error_condition(posix_errno errc e);

> > Returns: `error_condition(static_cast<int>(e), posixgeneric_category)`.

Rationale:

Names Considered
`portable` | Too non-specific. Did not wish to reserve such a common word in namespace std. Not quite the right meaning, either.
`portable_error` | Too long. Explicit qualification is always required for scoped enums, so a short name is desirable. Not quite the right meaning, either. May be misleading because `*_error` in the std lib is usually an exception class name.
`std_error` | Fairly short, yet explicit. But in fully qualified names like `std::std_error::not_enough_memory`, the std_ would be unfortunate. Not quite the right meaning, either. May be misleading because `*_error` in the std lib is usually an exception class name.
`generic` | Short enough. The category could be `generic_category`. Fully qualified names like `std::generic::not_enough_memory` read well. Reserving in namespace std seems dicey.
`generic_error` | Longish. The category could be `generic_category`. Fully qualified names like `std::generic_error::not_enough_memory` read well. Misleading because `*_error` in the std lib is usually an exception class name.
`generic_err` | A bit less longish. The category could be `generic_category`. Fully qualified names like `std::generic_err::not_enough_memory` read well.
`gen_err` | Shorter still. The category could be `generic_category`. Fully qualified names like `std::gen_err::not_enough_memory` read well.
`generr` | Shorter still. The category could be `generic_category`. Fully qualified names like `std::generr::not_enough_memory` read well.
`error` | Shorter still. The category could be `generic_category`. Fully qualified names like `std::error::not_enough_memory` read well. Do we want to use this general a name?
`err` | Shorter still. The category could be `generic_category`. Fully qualified names like `std::err::not_enough_memory` read well. Although alone it looks odd as a name, given the existing `errno` and `namespace std` names, it seems fairly intuitive. Problem: `err` is used throughout the standard library as an argument name and in examples as a variable name; it seems too confusing to add yet another use of the name.
`errc` | Short enough. The "c" stands for "constant". The category could be `generic_category`. Fully qualified names like `std::errc::not_enough_memory` read well. Although alone it looks odd as a name, given the existing `errno` and `namespace std` names, it seems fairly intuitive. There are no uses of `errc` in the current C++ standard.

### 806. `unique_ptr::reset` effects incorrect, too permissive

Section: 20.8.14.2.5 [unique.ptr.single.modifiers] Status: CD1 Submitter: Peter Dimov Opened: 2008-03-13 Last modified: 2008-09-26

View all other issues in [unique.ptr.single.modifiers].

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Discussion:

`void unique_ptr::reset(T* p = 0)` is currently specified as:

> Effects: If `p == get()` there are no effects. Otherwise `get_deleter()(get())`.

There are two problems with this. One, if `get() == 0` and `p != 0`, the deleter is called with a NULL pointer, and this is probably not what's intended (the destructor avoids calling the deleter with 0.)

Two, the special check for `get() == p` is generally not needed and such a situation usually indicates an error in the client code, which is being masked. As a data point, `boost::shared_ptr` was changed to assert on such self-resets in 2001 and there were no complaints.

One might think that self-resets are necessary for operator= to work; it's specified to perform

>     reset( u.release() );

and the self-assignment

>     p = move(p);

might appear to result in a self-reset. But it doesn't; the `release()` is performed first, zeroing the stored pointer. In other words, `p.reset( q.release() )` works even when `p` and `q` are the same `unique_ptr`, and there is no need to special-case `p.reset( q.get() )` to work in a similar scenario, as it definitely doesn't when `p` and `q` are separate.

Proposed resolution:

Change 20.8.14.2.5 [unique.ptr.single.modifiers]:

>     void reset(T* p = 0);

> > -4- Effects: If `p == get() == 0` there are no effects. Otherwise `get_deleter()(get())`.

Change 20.8.14.3.3 [unique.ptr.runtime.modifiers]:

>     void reset(T* p = 0);

> > ...

> > -2- Effects: If `p == get() == 0` there are no effects. Otherwise `get_deleter()(get())`.

### 807. `tuple` construction should not fail unless its element's construction fails

Section: 20.5.2.1 [tuple.cnstr] Status: CD1 Submitter: Howard Hinnant Opened: 2008-03-13 Last modified: 2008-09-26

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Discussion:

527 Added a throws clause to `bind` constructors. I believe the same throws clause should be added to `tuple` except it ought to take into account move constructors as well.

Proposed resolution:

Add to 20.5.2.1 [tuple.cnstr]:

> For each `tuple` constructor and assignment operator, an exception is thrown only if the construction or assignment of one of the types in `Types` throws an exception.

### 808. [forward] incorrect redundant specification

Section: 20.3.3 [forward] Status: CD1 Submitter: Jens Maurer Opened: 2008-03-13 Last modified: 2008-09-26

View all other issues in [forward].

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Discussion:

p4 (forward) says:

> Return type: If `T` is an lvalue-reference type, an lvalue; otherwise, an rvalue.

First of all, lvalue-ness and rvalue-ness are properties of an expression, not of a type (see 3.10 [basic.lval]). Thus, the phrasing "Return type" is wrong. Second, the phrase says exactly what the core language wording says for folding references in 14.4.1 [temp.arg.type]/p4 and for function return values in 5.2.2 [expr.call]/p10. (If we feel the wording should be retained, it should at most be a note with cross-references to those sections.)

The prose after the example talks about "forwarding as an `int&` (an lvalue)" etc. In my opinion, this is a category error: "`int&`" is a type, "lvalue" is a property of an expression, orthogonal to its type. (Btw, expressions cannot have reference type, ever.)

Similar with move:

> Return type: an rvalue.

is just wrong and also redundant.

Proposed resolution:

Change 20.3.3 [forward] as indicated:

>     template <class T> T&& forward(typename identity<T>::type&& t);

> > ...

> > Return type: If `T` is an lvalue-reference type, an lvalue; otherwise, an rvalue.

> > ...

> > -7- In the first call to `factory`, `A1` is deduced as `int`, so 2 is forwarded to `A`'s constructor as an `int&&` (an rvalue). In the second call to factory, `A1` is deduced as `int&`, so `i` is forwarded to `A`'s constructor as an `int&` (an lvalue). In both cases, `A2` is deduced as double, so 1.414 is forwarded to `A`'s constructor as `double&&` (an rvalue).

>     template <class T> typename remove_reference<T>::type&& move(T&& t);

> > ...

> > Return type: an rvalue.

### 809. std::swap should be overloaded for array types

Section: 25.3.3 [alg.swap] Status: CD1 Submitter: Niels Dekker Opened: 2008-02-28 Last modified: 2008-09-26

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Discussion:

For the sake of generic programming, the header `<algorithm>` should provide an overload of `std::swap` for array types:

    template<class T, size_t N> void swap(T (&a)[N], T (&b)[N]);

It became apparent to me that this overload is missing, when I considered how to write a swap function for a generic wrapper class template. (Actually I was thinking of Boost's value_initialized.) Please look at the following template, `W`, and suppose that is intended to be a very generic wrapper:

    template<class T> class W {
    public:
       T data;
    };

Clearly `W<T>` is CopyConstructible and CopyAssignable, and therefore Swappable, whenever `T` is CopyConstructible and CopyAssignable. Moreover, `W<T>` is also Swappable when `T` is an array type whose element type is CopyConstructible and CopyAssignable. Still it is recommended to add a custom swap function template to such a class template, for the sake of efficiency and exception safety. (E.g., Scott Meyers, Effective C++, Third Edition, item 25: Consider support for a non-throwing swap.) This function template is typically written as follows:

    template<class T> void swap(W<T>& x, W<T>& y) {
      using std::swap;
      swap(x.data, y.data);
    }

Unfortunately, this will introduce an undesirable inconsistency, when `T` is an array. For instance, `W<std::string[8]>` is Swappable, but the current Standard does not allow calling the custom swap function that was especially written for `W`!

    W<std::string[8]> w1, w2;  // Two objects of a Swappable type.
    std::swap(w1, w2);  // Well-defined, but inefficient.
    using std::swap;
    swap(w1, w2);  // Ill-formed, just because ADL finds W's swap function!!!

`W`'s `swap` function would try to call `std::swap` for an array, `std::string[8]`, which is not supported by the Standard Library. This issue is easily solved by providing an overload of `std::swap` for array types. This swap function should be implemented in terms of swapping the elements of the arrays, so that it would be non-throwing for arrays whose element types have a non-throwing swap.

Note that such an overload of `std::swap` should also support multi-dimensional arrays. Fortunately that isn't really an issue, because it would do so automatically, by means of recursion.

For your information, there was a discussion on this issue at comp.lang.c++.moderated: [Standard Library] Shouldn't std::swap be overloaded for C-style arrays?

Proposed resolution:

Add an extra condition to the definition of Swappable requirements [swappable] in 20.2.1 [utility.arg.requirements]:

> - `T` is `Swappable` if `T` is an array type whose element type is `Swappable`.

Add the following to 25.3.3 [alg.swap]:

>     template<class T, size_t N> void swap(T (&a)[N], T (&b)[N]);

> > Requires: Type `T` shall be `Swappable`.

> > Effects: `swap_ranges(a, a + N, b);`

### 810. Missing traits dependencies in operational semantics of extended manipulators

Section: 27.7.4 [ext.manip] Status: WP Submitter: Daniel Krügler Opened: 2008-03-01 Last modified: 2009-07-18

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Discussion:

The recent draft (as well as the original proposal n2072) uses an operational semantic for `get_money` ([ext.manip]/4) and `put_money` ([ext.manip]/6), which uses

>     istreambuf_iterator<charT>

and

>     ostreambuf_iterator<charT>

resp, instead of the iterator instances, with explicitly provided traits argument (The operational semantic defined by `f` is also traits dependent). This is an obvious oversight because both `*stream_buf` c'tors expect a `basic_streambuf<charT,traits>` as argument.

The same problem occurs within the `get_time` and `put_time` semantic where additional to the problem we have an editorial issue in `get_time` (`streambuf_iterator` instead of `istreambuf_iterator`).

[ Batavia (2009-05): ]

> This appears to be an issue of presentation.

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

In 27.7.4 [ext.manip]/4 within function `f` replace the first line

>     template <class charT, class traits, class moneyT>
>     void f(basic_ios<charT, traits>& str, moneyT& mon, bool intl) {
>        typedef istreambuf_iterator<charT, traits> Iter;
>        ...

In 27.7.4 [ext.manip]/5 remove the first template `charT` parameter:

>     template <class charT, class moneyT> unspecified put_money(const moneyT& mon, bool intl = false);

In 27.7.4 [ext.manip]/6 within function `f` replace the first line

>     template <class charT, class traits, class moneyT>
>     void f(basic_ios<charT, traits>& str, const moneyT& mon, bool intl) {
>       typedef ostreambuf_iterator<charT, traits> Iter;
>       ...

In 27.7.4 [ext.manip]/8 within function `f` replace the first line

>     template <class charT, class traits>
>     void f(basic_ios<charT, traits>& str, struct tm *tmb, const charT *fmt) {
>       typedef istreambuf_iterator<charT, traits> Iter;
>       ...

In 27.7.4 [ext.manip]/10 within function `f` replace the first line

>     template <class charT, class traits>
>     void f(basic_ios<charT, traits>& str, const struct tm *tmb, const charT *fmt) {
>       typedef ostreambuf_iterator<charT, traits> Iter;
>       ...

In 27.7 [iostream.format], Header `<iomanip>` synopsis change:

>     template <class charT, class moneyT> T8 put_money(const moneyT& mon, bool intl = false);

### 813. "empty" undefined for `shared_ptr`

Section: 20.8.15.2 [util.smartptr.shared] Status: CD1 Submitter: Matt Austern Opened: 2008-02-26 Last modified: 2008-09-26

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Discussion:

Several places in 20.8.15.2 [util.smartptr.shared] refer to an "empty" `shared_ptr`. However, that term is nowhere defined. The closest thing we have to a definition is that the default constructor creates an empty `shared_ptr` and that a copy of a default-constructed `shared_ptr` is empty. Are any other `shared_ptr`s empty? For example, is `shared_ptr((T*) 0)` empty? What are the properties of an empty `shared_ptr`? We should either clarify this term or stop using it.

One reason it's not good enough to leave this term up to the reader's intuition is that, in light of N2351 and issue 711, most readers' intuitive understanding is likely to be wrong. Intuitively one might expect that an empty `shared_ptr` is one that doesn't store a pointer, but, whatever the definition is, that isn't it.

[ Peter adds: ]

> Or, what is an "empty" `shared_ptr`?

> - Are any other `shared_ptrs` empty?

>   Yes. Whether a given `shared_ptr` instance is empty or not is (*) completely specified by the last mutating operation on that instance. Give me an example and I'll tell you whether the `shared_ptr` is empty or not.

>   > (*) If it isn't, this is a legitimate defect.

> - For example, is `shared_ptr((T*) 0)` empty?

>   No. If it were empty, it would have a `use_count()` of 0, whereas it is specified to have an `use_count()` of 1.

> - What are the properties of an empty `shared_ptr`?

>   The properties of an empty `shared_ptr` can be derived from the specification. One example is that its destructor is a no-op. Another is that its `use_count()` returns 0. I can enumerate the full list if you really like.

> - We should either clarify this term or stop using it.

>   I don't agree with the imperative tone

>   A clarification would be either a no-op - if it doesn't contradict the existing wording - or a big mistake if it does.

>   I agree that a clarification that is formally a no-op may add value.

> - However, that term is nowhere defined.

>   Terms can be useful without a definition. Consider the following simplistic example. We have a type `X` with the following operations defined:

>   >     X x;
>   >     X x2(x);
>   >     X f(X x);
>   >     X g(X x1, X x2);

>   A default-constructed value is green.
>   A copy has the same color as the original.
>   `f(x)` returns a red value if the argument is green, a green value otherwise.
>   `g(x1,x2)` returns a green value if the arguments are of the same color, a red value otherwise.

>   Given these definitions, you can determine the color of every instance of type `X`, even if you have absolutely no idea what green and red mean.

>   Green and red are "nowhere defined" and completely defined at the same time.

> Alisdair's wording is fine.

Proposed resolution:

Append the following sentance to 20.8.15.2 [util.smartptr.shared]

> The `shared_ptr` class template stores a pointer, usually obtained via `new`. `shared_ptr` implements semantics of shared ownership; the last remaining owner of the pointer is responsible for destroying the object, or otherwise releasing the resources associated with the stored pointer. A `shared_ptr` object that does not own a pointer is said to be empty.

### 814. `vector<bool>::swap(reference, reference)` not defined

Section: 23.3.7 [vector.bool] Status: WP Submitter: Alisdair Meredith Opened: 2008-03-17 Last modified: 2009-07-18

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Discussion:

`vector<bool>::swap(reference, reference)` has no definition.

[ San Francisco: ]

> Move to Open. Alisdair to provide a resolution.

[ Post Summit Daniel provided wording. ]

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Just after 23.3.7 [vector.bool]/5 add the following prototype and description:

> static void swap(reference x, reference y);

> > -6- Effects: Exchanges the contents of `x` and `y` as-if by:

> > >     bool b = x;
> > >     x = y;
> > >     y = b;

### 818. wording for memory ordering

Section: 29.3 [atomics.order] Status: CD1 Submitter: Jens Maurer Opened: 2008-03-22 Last modified: 2008-09-26

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Discussion:

29.3 [atomics.order] p1 says in the table that

> Element | Meaning
> --- | ---
> `memory_order_acq_rel` | the operation has both acquire and release semantics

To my naked eye, that seems to imply that even an atomic read has both acquire and release semantics.

Then, p1 says in the table:

> Element | Meaning
> --- | ---
> `memory_order_seq_cst` | the operation has both acquire and release semantics, and, in addition, has sequentially-consistent operation ordering

So that seems to be "the same thing" as `memory_order_acq_rel`, with additional constraints.

I'm then reading p2, where it says:

> The `memory_order_seq_cst` operations that load a value are acquire operations on the affected locations. The `memory_order_seq_cst` operations that store a value are release operations on the affected locations.

That seems to imply that atomic reads only have acquire semantics. If that is intended, does this also apply to `memory_order_acq_rel` and the individual load/store operations as well?

Also, the table in p1 contains phrases with "thus" that seem to indicate consequences of normative wording in 1.10 [intro.multithread]. That shouldn't be in normative text, for the fear of redundant or inconsistent specification with the other normative text.

Double-check 29.6 [atomics.types.operations] that each operation clearly says whether it's a load or a store operation, or both. (It could be clearer, IMO. Solution not in current proposed resolution.)

29.3 [atomics.order] p2: What's a "consistent execution"? It's not defined in 1.10 [intro.multithread], it's just used in notes there.

And why does 29.6 [atomics.types.operations] p9 for "load" say:

> Requires: The order argument shall not be `memory_order_acquire` nor `memory_order_acq_rel`.

(Since this is exactly the same restriction as for "store", it seems to be a typo.)

And then: 29.6 [atomics.types.operations] p12:

> These operations are read-modify-write operations in the sense of the "synchronizes with" definition (1.10 [intro.multithread]), so both such an operation and the evaluation that produced the input value synchronize with any evaluation that reads the updated value.

This is redundant with 1.10 [intro.multithread], see above for the reasoning.

[ San Francisco: ]

> Boehm: "I don't think that this changes anything terribly substantive, but it improves the text."

> Note that "Rephrase the table in as [sic] follows..." should read "Replace the table in [atomics.order] with the following...."

> The proposed resolution needs more work. Crowl volunteered to address all of the atomics issues in one paper.

> This issue is addressed in N2783.

Proposed resolution:

edit 29.3 [atomics.order], paragraph 1 as follows.

> The enumeration `memory_order` specifies the detailed regular (non-atomic) memory synchronization order as defined in Clause 1.7 section 1.10 and may provide for operation ordering. Its enumerated values and their meanings are as follows:

> > For `memory_order_relaxed`,
> >   no operation orders memory.
> > For `memory_order_release`, `memory_order_acq_rel`, and `memory_order_seq_cst`,
> >   a store operation performs a release operation on the affected memory location.
> > For `memory_order_consume`,
> >   a load operation performs a consume operation on the affected memory location.
> > For `memory_order_acquire`, `memory_order_acq_rel`, and `memory_order_seq_cst`,
> >   a load operation performs an acquire operation on the affected memory location.

remove table 136 in 29.3 [atomics.order].

> Table 136 — memory_order effects
> Element | Meaning
> --- | ---
> `memory_order_relaxed` | the operation does not order memory
> `memory_order_release` | the operation performs a release operation on the affected memory location, thus making regular memory writes visible to other threads through the atomic variable to which it is applied
> `memory_order_acquire` | the operation performs an acquire operation on the affected memory location, thus making regular memory writes in other threads released through the atomic variable to which it is applied visible to the current thread
> `memory_order_consume` | the operation performs a consume operation on the affected memory location, thus making regular memory writes in other threads released through the atomic variable to which it is applied visible to the regular memory reads that are dependencies of this consume operation.
> `memory_order_acq_rel` | the operation has both acquire and release semantics
> `memory_order_seq_cst` | the operation has both acquire and release semantics, and, in addition, has sequentially-consistent operation ordering

edit 29.3 [atomics.order], paragraph 2 as follows.

> The `memory_order_seq_cst` operations that load a value are acquire operations on the affected locations. The `memory_order_seq_cst` operations that store a value are release operations on the affected locations. In addition, in a consistent execution, there There must be is a single total order S on all `memory_order_seq_cst` operations, consistent with the happens before order and modification orders for all affected locations, such that each `memory_order_seq_cst` operation observes either the last preceding modification according to this order S, or the result of an operation that is not `memory_order_seq_cst`. [Note: Although it is not explicitly required that S include locks, it can always be extended to an order that does include lock and unlock operations, since the ordering between those is already included in the happens before ordering. —end note]

### 820. `current_exception()`'s interaction with throwing copy ctors

Section: 18.8.5 [propagation] Status: CD1 Submitter: Stephan T. Lavavej Opened: 2008-03-26 Last modified: 2008-09-26

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Discussion:

As of N2521, the Working Paper appears to be silent about what `current_exception()` should do if it tries to copy the currently handled exception and its copy constructor throws. 18.8.5 [propagation]/7 says "If the function needs to allocate memory and the attempt fails, it returns an `exception_ptr` object that refers to an instance of `bad_alloc`.", but doesn't say anything about what should happen if memory allocation succeeds but the actual copying fails.

I see three alternatives: (1) return an `exception_ptr` object that refers to an instance of some fixed exception type, (2) return an `exception_ptr` object that refers to an instance of the copy ctor's thrown exception (but if that has a throwing copy ctor, an infinite loop can occur), or (3) call `terminate()`.

I believe that `terminate()` is the most reasonable course of action, but before we go implement that, I wanted to raise this issue.

[ Peter's summary: ]

> The current practice is to not have throwing copy constructors in exception classes, because this can lead to `terminate()` as described in 15.5.1 [except.terminate]. Thus calling `terminate()` in this situation seems consistent and does not introduce any new problems.

> However, the resolution of core issue 475 may relax this requirement:

> > The CWG agreed with the position that `std::uncaught_exception()` should return `false` during the copy to the exception object and that `std::terminate()` should not be called if that constructor exits with an exception.

> Since throwing copy constructors will no longer call `terminate()`, option (3) doesn't seem reasonable as it is deemed too drastic a response in a recoverable situation.

> Option (2) cannot be adopted by itself, because a potential infinite recursion will need to be terminated by one of the other options.

Proposed resolution:

Add the following paragraph after 18.8.5 [propagation]/7:

> Returns (continued): If the attempt to copy the current exception object throws an exception, the function returns an `exception_ptr` that refers to the thrown exception or, if this is not possible, to an instance of `bad_exception`.

> [Note: The copy constructor of the thrown exception may also fail, so the implementation is allowed to substitute a `bad_exception` to avoid infinite recursion. -- end note.]

Rationale:

[ San Francisco: ]

> Pete: there may be an implied assumption in the proposed wording that current_exception() copies the existing exception object; the implementation may not actually do that.

> Pete will make the required editorial tweaks to rectify this.

### 821. Minor cleanup : `unique_ptr`

Section: 20.8.14.3.3 [unique.ptr.runtime.modifiers] Status: WP Submitter: Alisdair Meredith Opened: 2008-03-30 Last modified: 2009-03-09

View all issues with WP status.

Discussion:

Reading resolution of LWG issue 673 I noticed the following:

>     void reset(T* pointer p = 0 pointer());

> -1- Requires: Does not accept pointer types which are convertible to `T*` `pointer` (diagnostic required). [Note: One implementation technique is to create a private templated overload. -- end note]

This could be cleaned up by mandating the overload as a public deleted function. In addition, we should probably overload `reset` on `nullptr_t` to be a stronger match than the deleted overload. Words...

Proposed resolution:

Add to class template definition in 20.8.14.3 [unique.ptr.runtime]

>     // modifiers
>     pointer release();
>     void reset(pointer p = pointer());
>     void reset( nullptr_t );
>     template< typename U > void reset( U ) = delete;
>     void swap(unique_ptr&& u);

Update 20.8.14.3.3 [unique.ptr.runtime.modifiers]

>     void reset(pointer p = pointer());
>     void reset(nullptr_t);

> -1- Requires: Does not accept pointer types which are convertible to `pointer` (diagnostic required). [Note: One implementation technique is to create a private templated overload. -- end note]

> Effects: If `get() == nullptr` there are no effects. Otherwise `get_deleter()(get())`.

> ...

[ Note this wording incorporates resolutions for 806 (New) and 673 (Ready). ]

### 822. Object with explicit copy constructor no longer `CopyConstructible`

Section: 20.2.1 [utility.arg.requirements] Status: WP Submitter: James Kanze Opened: 2008-04-01 Last modified: 2009-10-26

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Discussion:

I just noticed that the following program is legal in C++03, but is forbidden in the current draft:

>     #include <vector>
>     #include <iostream>

>     class Toto
>     {
>     public:
>         Toto() {}
>         explicit Toto( Toto const& ) {}
>     } ;

>     int
>     main()
>     {
>         std::vector< Toto > v( 10 ) ;
>         return 0 ;
>     }

Is this change intentional? (And if so, what is the justification? I wouldn't call such code good, but I don't see any reason to break it unless we get something else in return.)

[ San Francisco: ]

> The subgroup that looked at this felt this was a good change, but it may already be handled by incoming concepts (we're not sure).

[ Post Summit: ]

> Alisdair: Proposed resolution kinda funky as these tables no longer exist. Move from direct init to copy init. Clarify with Doug, recommends NAD.

> Walter: Suggest NAD via introduction of concepts.

> Recommend close as NAD.

[ 2009-07 Frankfurt: ]

> Need to look at again without concepts.

[ 2009-07 Frankfurt: ]

> Move to Ready with original proposed resolution.

> [Howard: Original proposed resolution restored.]

Proposed resolution:

In 20.2.1 [utility.arg.requirements] change Table 33: `MoveConstructible` requirements [moveconstructible]:

> expression | post-condition
> --- | ---
> `T t(rv) = rv` | `t` is equivalent to the value of `rv` before the construction
> ...

In 20.2.1 [utility.arg.requirements] change Table 34: `CopyConstructible` requirements [copyconstructible]:

> expression | post-condition
> --- | ---
> `T t(u) = u` | the value of `u` is unchanged and is equivalent to `t`
> ...

### 824. rvalue ref issue with `basic_string` inserter

Section: 21.4.8.9 [string.io] Status: CD1 Submitter: Alisdair Meredith Opened: 2008-04-10 Last modified: 2008-09-26

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Discussion:

In the current working paper, the `<string>` header synopsis at the end of 21.3 [string.classes] lists a single `operator<<` overload for `basic_string`.

>     template<class charT, class traits, class Allocator>
>      basic_ostream<charT, traits>&
>        operator<<(basic_ostream<charT, traits>&& os,
>                   const basic_string<charT,traits,Allocator>& str);

The definition in 21.4.8.9 [string.io] lists two:

>     template<class charT, class traits, class Allocator>
>      basic_ostream<charT, traits>&
>        operator<<(basic_ostream<charT, traits>& os,
>                   const basic_string<charT,traits,Allocator>& str);

>     template<class charT, class traits, class Allocator>
>      basic_ostream<charT, traits>&
>        operator<<(basic_ostream<charT, traits>&& os,
>                   const basic_string<charT,traits,Allocator>& str);

I believe the synopsis in 21.3 [string.classes] is correct, and the first of the two signatures in 21.4.8.9 [string.io] should be deleted.

Proposed resolution:

Delete the first of the two signatures in 21.4.8.9 [string.io]:

>     template<class charT, class traits, class Allocator>
>      basic_ostream<charT, traits>&
>        operator<<(basic_ostream<charT, traits>& os,
>                   const basic_string<charT,traits,Allocator>& str);

>     template<class charT, class traits, class Allocator>
>      basic_ostream<charT, traits>&
>        operator<<(basic_ostream<charT, traits>&& os,
>                   const basic_string<charT,traits,Allocator>& str);

### 829. current_exception wording unclear about exception type

Section: 18.8.5 [propagation] Status: CD1 Submitter: Beman Dawes Opened: 2008-04-20 Last modified: 2008-09-26

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Discussion:

Consider this code:

>     exception_ptr xp;

>     try {do_something(); }

>     catch (const runtime_error& ) {xp = current_exception();}

>     ...

>     rethrow_exception(xp);

Say `do_something()` throws an exception object of type `range_error`. What is the type of the exception object thrown by `rethrow_exception(xp)` above? It must have a type of `range_error`; if it were of type `runtime_error` it still isn't possible to propagate an exception and the exception_ptr/current_exception/rethrow_exception machinery serves no useful purpose.

Unfortunately, the current wording does not explicitly say that. Different people read the current wording and come to different conclusions. While it may be possible to deduce the correct type from the current wording, it would be much clearer to come right out and explicitly say what the type of the referred to exception is.

[ Peter adds: ]

> I don't like the proposed resolution of 829. The normative text is unambiguous that the `exception_ptr` refers to the currently handled exception. This term has a standard meaning, see 15.3 [except.handle]/8; this is the exception that `throw;` would rethrow, see 15.1 [except.throw]/7.

> A better way to address this is to simply add the non-normative example in question as a clarification. The term currently handled exception should be italicized and cross-referenced. A [Note: the currently handled exception is the exception that a throw expression without an operand (15.1 [except.throw]/7) would rethrow. --end note] is also an option.

Proposed resolution:

After 18.8.5 [propagation] , paragraph 7, add the indicated text:

>     exception_ptr current_exception();

> > Returns: `exception_ptr` object that refers to the currently handled exception (15.3 [except.handle]) or a copy of the currently handled exception, or a null `exception_ptr` object if no exception is being handled. If the function needs to allocate memory and the attempt fails, it returns an `exception_ptr` object that refers to an instance of `bad_alloc`. It is unspecified whether the return values of two successive calls to `current_exception` refer to the same exception object. [Note: that is, it is unspecified whether `current_exception` creates a new copy each time it is called. -- end note]

> > Throws: nothing.

### 838. can an end-of-stream iterator become a non-end-of-stream one?

Section: 24.6.1 [istream.iterator] Status: WP Submitter: Martin Sebor Opened: 2008-05-17 Last modified: 2009-10-26

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Discussion:

From message c++std-lib-20003...

The description of `istream_iterator` in 24.6.1 [istream.iterator], p1 specifies that objects of the class become the end-of-stream (EOS) iterators under the following condition (see also issue 788 another problem with this paragraph):

> If the end of stream is reached (`operator void*()` on the stream returns `false`), the iterator becomes equal to the end-of-stream iterator value.

One possible implementation approach that has been used in practice is for the iterator to set its `in_stream` pointer to 0 when it reaches the end of the stream, just like the default ctor does on initialization. The problem with this approach is that the Effects clause for `operator++()` says the iterator unconditionally extracts the next value from the stream by evaluating `*in_stream >> value`, without checking for `(in_stream == 0)`.

Conformance to the requirement outlined in the Effects clause can easily be verified in programs by setting `eofbit` or `failbit` in `exceptions()` of the associated stream and attempting to iterate past the end of the stream: each past-the-end access should trigger an exception. This suggests that some other, more elaborate technique might be intended.

Another approach, one that allows `operator++()` to attempt to extract the value even for EOS iterators (just as long as `in_stream` is non-0) is for the iterator to maintain a flag indicating whether it has reached the end of the stream. This technique would satisfy the presumed requirement implied by the Effects clause mentioned above, but it isn't supported by the exposition-only members of the class (no such flag is shown). This approach is also found in existing practice.

The inconsistency between existing implementations raises the question of whether the intent of the specification is that a non-EOS iterator that has reached the EOS become a non-EOS one again after the stream's `eofbit` flag has been cleared? That is, are the assertions in the program below expected to pass?

>        sstream strm ("1 ");
>        istream_iterator eos;
>        istream_iterator it (strm);
>        int i;
>        i = *it++
>        assert (it == eos);
>        strm.clear ();
>        strm << "2 3 ";
>        assert (it != eos);
>        i = *++it;
>        assert (3 == i);

Or is it intended that once an iterator becomes EOS it stays EOS until the end of its lifetime?

[ San Francisco: ]

> We like the direction of the proposed resolution. We're not sure about the wording, and we need more time to reflect on it,

> Move to Open. Detlef to rewrite the proposed resolution in such a way that no reference is made to exposition only members of `istream_iterator`.

[ 2009-07 Frankfurt: ]

> Move to Ready.

Proposed resolution:

The discussion of this issue on the reflector suggests that the intent of the standard is for an `istreambuf_iterator` that has reached the EOS to remain in the EOS state until the end of its lifetime. Implementations that permit EOS iterators to return to a non-EOS state may only do so as an extension, and only as a result of calling `istream_iterator` member functions on EOS iterators whose behavior is in this case undefined.

To this end we propose to change 24.6.1 [istream.iterator], p1, as follows:

> The result of operator-> on an end-of-stream is not defined. For any other iterator value a `const T*` is returned. Invoking `operator++()` on an end-of-stream iterator is undefined. It is impossible to store things into istream iterators...

Add pre/postconditions to the member function descriptions of `istream_iterator` like so:

>     istream_iterator();

> Effects: Constructs the end-of-stream iterator.
> Postcondition: `in_stream == 0`.

>     istream_iterator(istream_type &s);

> Effects: Initializes `in_stream` with &s. value may be initialized during construction or the first time it is referenced.
> Postcondition: `in_stream == &s`.

>     istream_iterator(const istream_iterator &x);

> Effects: Constructs a copy of `x`.
> Postcondition: `in_stream == x.in_stream`.

>     istream_iterator& operator++();

> Requires: `in_stream != 0`.
> Effects: `*in_stream >> value`.

>     istream_iterator& operator++(int);

> Requires: `in_stream != 0`.
> Effects:

> >     istream_iterator tmp (*this);
> >     *in_stream >> value;
> >     return tmp;

### 842. ConstructibleAsElement and bit containers

Section: 23.2 [container.requirements], 23.3.7 [vector.bool], 20.3.7 [template.bitset] Status: CD1 Submitter: Howard Hinnant Opened: 2008-06-03 Last modified: 2008-09-26

View other active issues in [container.requirements].

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Discussion:

23.2 [container.requirements]/p3 says:

> Objects stored in these components shall be constructed using `construct_element` (20.6.9). For each operation that inserts an element of type `T` into a container (`insert`, `push_back`, `push_front`, `emplace`, etc.) with arguments `args... T` shall be `ConstructibleAsElement`, as described in table 88. [Note: If the component is instantiated with a scoped allocator of type `A` (i.e., an allocator for which `is_scoped_allocator<A>::value` is `true`), then `construct_element` may pass an inner allocator argument to `T`'s constructor. -- end note]

However `vector<bool, A>` (23.3.7 [vector.bool]) and `bitset<N>` (20.3.7 [template.bitset]) store bits, not `bool`s, and `bitset<N>` does not even have an allocator. But these containers are governed by this clause. Clearly this is not implementable.

Proposed resolution:

Change 23.2 [container.requirements]/p3:

> Objects stored in these components shall be constructed using `construct_element` (20.6.9), unless otherwise specified. For each operation that inserts an element of type `T` into a container (`insert`, `push_back`, `push_front`, `emplace`, etc.) with arguments `args... T` shall be `ConstructibleAsElement`, as described in table 88. [Note: If the component is instantiated with a scoped allocator of type `A` (i.e., an allocator for which `is_scoped_allocator<A>::value` is `true`), then `construct_element` may pass an inner allocator argument to `T`'s constructor. -- end note]

Change 23.3.7 [vector.bool]/p2:

> Unless described below, all operations have the same requirements and semantics as the primary `vector` template, except that operations dealing with the `bool` value type map to bit values in the container storage, and `construct_element` (23.2 [container.requirements]) is not used to construct these values.

Move 20.3.7 [template.bitset] to clause 20.

### 843. Reference Closure

Section: X [func.referenceclosure.cons] Status: CD1 Submitter: Lawrence Crowl Opened: 2008-06-02 Last modified: 2008-09-26

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Discussion:

The `std::reference_closure` type has a deleted copy assignment operator under the theory that references cannot be assigned, and hence the assignment of its reference member must necessarily be ill-formed.

However, other types, notably `std::reference_wrapper` and `std::function` provide for the "copying of references", and thus the current definition of `std::reference_closure` seems unnecessarily restrictive. In particular, it should be possible to write generic functions using both `std::function` and `std::reference_closure`, but this generality is much harder when one such type does not support assignment.

The definition of `reference_closure` does not necessarily imply direct implementation via reference types. Indeed, the `reference_closure` is best implemented via a frame pointer, for which there is no standard type.

The semantics of assignment are effectively obtained by use of the default destructor and default copy assignment operator via

>     x.~reference_closure(); new (x) reference_closure(y);

So the copy assignment operator generates no significant real burden to the implementation.

Proposed resolution:

In [func.referenceclosure] Class template reference_closure, replace the `=delete` in the copy assignment operator in the synopsis with `=default`.

>     template<class R , class... ArgTypes >
>       class reference_closure<R (ArgTypes...)> {
>       public:
>          ...
>          reference_closure& operator=(const reference_closure&) = delete default;
>          ...

In X [func.referenceclosure.cons] Construct, copy, destroy, add the member function description

>     reference_closure& operator=(const reference_closure& f)

> > Postcondition: `*this` is a copy of `f`.

> > Returns: `*this`.

### 844. `complex pow` return type is ambiguous

Section: 26.4.9 [cmplx.over] Status: CD1 Submitter: Howard Hinnant Opened: 2008-06-03 Last modified: 2009-03-21

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Discussion:

The current working draft is in an inconsistent state.

26.4.8 [complex.transcendentals] says that:

> `pow(complex<float>(), int())` returns a `complex<float>`.

26.4.9 [cmplx.over] says that:

> `pow(complex<float>(), int())` returns a `complex<double>`.

[ Sophia Antipolis: ]

> Since `int` promotes to `double`, and C99 doesn't have an `int`-based overload for `pow`, the C99 result is `complex<double>`, see also C99 7.22, see also library issue 550.

> Special note: ask P.J. Plauger.

> > Looks fine.

Proposed resolution:

Strike this `pow` overload in 26.4.1 [complex.syn] and in 26.4.8 [complex.transcendentals]:

>     template<class T> complex<T> pow(const complex<T>& x, int y);

### 845. atomics cannot support aggregate initialization

Section: 29.5 [atomics.types] Status: CD1 Submitter: Alisdair Meredith Opened: 2008-06-03 Last modified: 2008-09-26

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Discussion:

The atomic classes (and class templates) are required to support aggregate initialization (29.5.1 [atomics.types.integral]p2 / 29.5.2 [atomics.types.address]p1) yet also have user declared constructors, so cannot be aggregates.

This problem might be solved with the introduction of the proposed initialization syntax at Antipolis, but the wording above should be altered. Either strike the sentence as redundant with new syntax, or refer to 'brace initialization'.

[ Jens adds: ]

> Note that

> >     atomic_itype a1 = { 5 };

> would be aggregate-initialization syntax (now coming under the disguise of brace initialization), but would be ill-formed, because the corresponding constructor for atomic_itype is explicit. This works, though:

> >     atomic_itype a2 { 6 };

[ San Francisco: ]

> The preferred approach to resolving this is to remove the explicit specifiers from the atomic integral type constructors.

> Lawrence will provide wording.

> This issue is addressed in N2783.

Proposed resolution:

within the synopsis in 29.5.1 [atomics.types.integral] edit as follows.

>     ....
>     typedef struct atomic_bool {
>     ....
>       constexpr explicit atomic_bool(bool);
>     ....
>     typedef struct atomic_itype {
>     ....
>       constexpr explicit atomic_itype(integral);
>     ....

edit 29.5.1 [atomics.types.integral] paragraph 2 as follows.

> The atomic integral types shall have standard layout. They shall each have a trivial default constructor, a constexpr explicit value constructor, a deleted copy constructor, a deleted copy assignment operator, and a trivial destructor. They shall each support aggregate initialization syntax.

within the synopsis of 29.5.2 [atomics.types.address] edit as follows.

>     ....
>     typedef struct atomic_address {
>     ....
>       constexpr explicit atomic_address(void*);
>     ....

edit 29.5.2 [atomics.types.address] paragraph 1 as follows.

> The type `atomic_address` shall have standard layout. It shall have a trivial default constructor, a constexpr explicit value constructor, a deleted copy constructor, a deleted copy assignment operator, and a trivial destructor. It shall support aggregate initialization syntax.

within the synopsis of 29.5.3 [atomics.types.generic] edit as follows.

>     ....
>     template <class T> struct atomic {
>     ....
>       constexpr explicit atomic(T);
>     ....
>     template <> struct atomic<integral> : atomic_itype {
>     ....
>       constexpr explicit atomic(integral);
>     ....
>     template <> struct atomic<T*> : atomic_address {
>     ....
>       constexpr explicit atomic(T*);
>     ....

edit 29.5.3 [atomics.types.generic] paragraph 2 as follows.

> Specializations of the `atomic` template shall have a deleted copy constructor, a deleted copy assignment operator, and a constexpr explicit value constructor.

### 846. No definition for constructor

Section: 29.5 [atomics.types] Status: CD1 Submitter: Alisdair Meredith Opened: 2008-06-03 Last modified: 2008-09-26

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Discussion:

The atomic classes and class templates (29.5.1 [atomics.types.integral] / 29.5.2 [atomics.types.address]) have a constexpr constructor taking a value of the appropriate type for that atomic. However, neither clause provides semantics or a definition for this constructor. I'm not sure if the initialization is implied by use of constexpr keyword (which restricts the form of a constructor) but even if that is the case, I think it is worth spelling out explicitly as the inference would be far too subtle in that case.

[ San Francisco: ]

> Lawrence will provide wording.

> This issue is addressed in N2783.

Proposed resolution:

before the description of ...`is_lock_free`, that is before 29.6 [atomics.types.operations] paragraph 4, add the following description.

>     constexpr A::A(C desired);

> Effects:
>   Initializes the object with the value `desired`. [Note: Construction is not atomic. —end note]

### 847. string exception safety guarantees

Section: 21.4.1 [string.require] Status: WP Submitter: Hervé Brönnimann Opened: 2008-06-05 Last modified: 2009-10-26

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Discussion:

In March, on comp.lang.c++.moderated, I asked what were the string exception safety guarantees are, because I cannot see *any* in the working paper, and any implementation I know offers the strong exception safety guarantee (string unchanged if a member throws exception). The closest the current draft comes to offering any guarantees is 21.4 [basic.string], para 3:

> The class template `basic_string` conforms to the requirements for a Sequence Container (23.1.1), for a Reversible Container (23.1), and for an Allocator-aware container (91). The iterators supported by `basic_string` are random access iterators (24.1.5).

However, the chapter 23 only says, on the topic of exceptions: 23.2 [container.requirements], para 10:

> Unless otherwise specified (see 23.2.2.3 and 23.2.6.4) all container types defined in this clause meet the following additional requirements:

> - if an exception is thrown by...

I take it as saying that this paragraph has *no* implication on `std::basic_string`, as `basic_string` isn't defined in Clause 23 and this paragraph does not define a *requirement* of Sequence nor Reversible Container, just of the models defined in Clause 23. In addition, LWG Issue 718 proposes to remove 23.2 [container.requirements], para 3.

Finally, the fact that no operation on Traits should throw exceptions has no bearing, except to suggest (since the only other throws should be allocation, `out_of_range`, or `length_error`) that the strong exception guarantee can be achieved.

The reaction in that group by Niels Dekker, Martin Sebor, and Bo Persson, was all that this would be worth an LWG issue.

A related issue is that `erase()` does not throw. This should be stated somewhere (and again, I don't think that the 23.2 [container.requirements], para 1 applies here).

[ San Francisco: ]

> Implementors will study this to confirm that it is actually possible.

[ Daniel adds 2009-02-14: ]

> The proposed resolution of paper N2815 interacts with this issue (the paper does not refer to this issue).

[ 2009-07 Frankfurt: ]

> Move to Ready.

Proposed resolution:

Add a blanket statement in 21.4.1 [string.require]:

> - if any member function or operator of `basic_string<charT, traits, Allocator>` throws, that function or operator has no effect.

> - no `erase()` or `pop_back()` function throws.

As far as I can tell, this is achieved by any implementation. If I made a mistake and it is not possible to offer this guarantee, then either state all the functions for which this is possible (certainly at least `operator+=`, `append`, `assign`, and `insert`), or add paragraphs to Effects clauses wherever appropriate.

### 848. missing `std::hash` specializations for `std::bitset/std::vector<bool>`

Section: 20.7.16 [unord.hash] Status: CD1 Submitter: Thorsten Ottosen Opened: 2008-06-05 Last modified: 2008-09-26

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Discussion:

In the current working draft, `std::hash<T>` is specialized for builtin types and a few other types. Bitsets seems like one that is missing from the list, not because it cannot not be done by the user, but because it is hard or impossible to write an efficient implementation that works on 32bit/64bit chunks at a time. For example, `std::bitset` is too much encapsulated in this respect.

Proposed resolution:

Add the following to the synopsis in 20.7 [function.objects]/2:

>     template<class Allocator> struct hash<std::vector<bool,Allocator>>;
>     template<size_t N> struct hash<std::bitset<N>>;

Modify the last sentence of 20.7.16 [unord.hash]/1 to end with:

> ... and `std::string`, `std::u16string`, `std::u32string`, `std::wstring`, `std::error_code`, `std::thread::id`, `std::bitset`, `and std::vector<bool>`.

### 850. Should `shrink_to_fit` apply to `std::deque`?

Section: 23.3.2.2 [deque.capacity] Status: CD1 Submitter: Niels Dekker Opened: 2008-06-05 Last modified: 2008-09-26

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Discussion:

Issue 755 added a `shrink_to_fit` function to `std::vector` and `std::string`. It did not yet deal with `std::deque`, because of the fundamental difference between `std::deque` and the other two container types. The need for `std::deque` may seem less evident, because one might think that for this container, the overhead is a small map, and some number of blocks that's bounded by a small constant.

The container overhead can in fact be arbitrarily large (i.e. is not necessarily O(N) where N is the number of elements currently held by the `deque`). As Bill Plauger noted in a reflector message, unless the map of block pointers is shrunk, it must hold at least maxN/B pointers where maxN is the maximum of N over the lifetime of the `deque` since its creation. This is independent of how the map is implemented (`vector`-like circular buffer and all), and maxN bears no relation to N, the number of elements it currently holds.

Hervé Brönnimann reports a situation where a `deque` of requests grew very large due to some temporary backup (the front request hanging), and the map of the `deque` grew quite large before getting back to normal. Just to put some color on it, assuming a `deque` with 1K pointer elements in steady regime, that held, at some point in its lifetime, maxN=10M pointers, with one block holding 128 elements, the spine must be at least (maxN / 128), in that case 100K. In that case, shrink-to-fit would allow to reuse about 100K which would otherwise never be reclaimed in the lifetime of the `deque`.

An added bonus would be that it *allows* implementations to hang on to empty blocks at the end (but does not care if they do or not). A `shrink_to_fit` would take care of both shrinks, and guarantee that at most O(B) space is used in addition to the storage to hold the N elements and the N/B block pointers.

Proposed resolution:

To Class template deque 23.3.2 [deque] synopsis, add:

>     void shrink_to_fit();

To deque capacity 23.3.2.2 [deque.capacity], add:

>     void shrink_to_fit();

> > Remarks: `shrink_to_fit` is a non-binding request to reduce memory use. [Note: The request is non-binding to allow latitude for implementation-specific optimizations. -- end note]

### 852. unordered containers `begin(n)` mistakenly `const`

Section: 23.5 [unord] Status: CD1 Submitter: Robert Klarer Opened: 2008-06-12 Last modified: 2008-09-26

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Discussion:

In 3 of the four unordered containers the local `begin` member is mistakenly declared `const`:

>     local_iterator begin(size_type n) const;

Proposed resolution:

Change the synopsis in 23.5.1 [unord.map], 23.5.2 [unord.multimap], and 23.5.4 [unord.multiset]:

>     local_iterator begin(size_type n) const;

### 853. `to_string` needs updating with `zero` and `one`

Section: 20.3.7 [template.bitset] Status: WP Submitter: Howard Hinnant Opened: 2008-06-18 Last modified: 2009-07-18

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Discussion:

Issue 396 adds defaulted arguments to the `to_string` member, but neglects to update the three newer `to_string` overloads.

[ post San Francisco: ]

> Daniel found problems with the wording and provided fixes. Moved from Ready to Review.

[ Post Summit: ]

> Alisdair: suggest to not repeat the default arguments in B, C, D (definition of to_string members)

> Walter: This is not really a definition.

> Consensus: Add note to the editor: Please apply editor's judgement whether default arguments should be repeated for B, C, D changes.

> Recommend Tentatively Ready.

[ 2009-05-09: See alternative solution in issue 1113. ]

Proposed resolution:

1. replace in 20.3.7 [template.bitset]/1 (class `bitset`)

   >     template <class charT, class traits>
   >       basic_string<charT, traits, allocator<charT> >
   >       to_string(charT zero = charT('0'), charT one = charT('1')) const;
   >     template <class charT>
   >       basic_string<charT, char_traits<charT>, allocator<charT> >
   >       to_string(charT zero = charT('0'), charT one = charT('1')) const;
   >     basic_string<char, char_traits<char>, allocator<char> >
   >       to_string(char zero = '0', char one = '1') const;

2. replace in 20.3.7.2 [bitset.members]/37

   >     template <class charT, class traits>
   >       basic_string<charT, traits, allocator<charT> >
   >       to_string(charT zero = charT('0'), charT one = charT('1')) const;

   > > 37 Returns: `to_string<charT, traits, allocator<charT> >(zero, one)`.

3. replace in 20.3.7.2 [bitset.members]/38

   >     template <class charT>
   >       basic_string<charT, char_traits<charT>, allocator<charT> >
   >       to_string(charT zero = charT('0'), charT one = charT('1')) const;

   > > 38 Returns: `to_string<charT, char_traits<charT>, allocator<charT> >(zero, one)`.

4. replace in 20.3.7.2 [bitset.members]/39

   >     basic_string<char, char_traits<char>, allocator<char> >
   >       to_string(char zero = '0', char one = '1') const;

   > > 39 Returns: `to_string<char, char_traits<char>, allocator<char> >(zero, one)`.

### 856. Removal of `aligned_union`

Section: 20.6.7 [meta.trans.other] Status: CD1 Submitter: Jens Maurer Opened: 2008-06-12 Last modified: 2008-09-26

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Discussion:

With the arrival of extended unions (N2544), there is no known use of `aligned_union` that couldn't be handled by the "extended unions" core-language facility.

Proposed resolution:

Remove the following signature from 20.6.2 [meta.type.synop]:

>     template <std::size_t Len, class... Types> struct aligned_union;

Remove the second row from table 51 in 20.6.7 [meta.trans.other], starting with:

>     template <std::size_t Len,
>     class... Types>
>     struct aligned_union;

### 857. `condition_variable::time_wait` return `bool` error prone

Section: 30.5.1 [thread.condition.condvar] Status: WP Submitter: Beman Dawes Opened: 2008-06-13 Last modified: 2009-10-26

View other active issues in [thread.condition.condvar].

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Discussion:

The meaning of the `bool` returned by `condition_variable::timed_wait` is so obscure that even the class' designer can't deduce it correctly. Several people have independently stumbled on this issue.

It might be simpler to change the return type to a scoped enum:

>     enum class timeout { not_reached, reached };

That's the same cost as returning a `bool`, but not subject to mistakes. Your example below would be:

>     if (cv.wait_until(lk, time_limit) == timeout::reached )
>       throw time_out();

[ Beman to supply exact wording. ]

[ San Francisco: ]

> There is concern that the enumeration names are just as confusing, if not more so, as the bool. You might have awoken because of a signal or a spurious wakeup, for example.

> Group feels that this is a defect that needs fixing.

> Group prefers returning an enum over a void return.

> Howard to provide wording.

[ 2009-06-14 Beman provided wording. ]

[ 2009-07 Frankfurt: ]

> Move to Ready.

Proposed resolution:

Change Condition variables 30.5 [thread.condition], Header condition_variable synopsis, as indicated:

>     namespace std {
>       class condition_variable;
>       class condition_variable_any;

>       enum class cv_status { no_timeout, timeout };
>     }

Change Class condition_variable 30.5.1 [thread.condition.condvar] as indicated:

>     class condition_variable {
>     public:
>       ...
>       template <class Clock, class Duration>
>         bool cv_status wait_until(unique_lock<mutex>& lock,
>                         const chrono::time_point<Clock, Duration>& abs_time);
>       template <class Clock, class Duration, class Predicate>
>         bool wait_until(unique_lock<mutex>& lock,
>                         const chrono::time_point<Clock, Duration>& abs_time,
>                         Predicate pred);

>       template <class Rep, class Period>
>         bool cv_status wait_for(unique_lock<mutex>& lock,
>                       const chrono::duration<Rep, Period>& rel_time);
>       template <class Rep, class Period, class Predicate>
>         bool wait_for(unique_lock<mutex>& lock,
>                       const chrono::duration<Rep, Period>& rel_time,
>                       Predicate pred);
>       ...
>     };

>     ...

>     template <class Clock, class Duration>
>       bool cv_status wait_until(unique_lock<mutex>& lock,
>                       const chrono::time_point<Clock, Duration>& abs_time);

> > -15- Precondition: `lock` is locked by the calling thread, and either

> > - no other thread is waiting on this `condition_variable` object or
> > - `lock.mutex()` returns the same value for each of the `lock` arguments supplied by all concurrently waiting threads (via `wait`, `wait_for` or `wait_until`.).

> > -16- Effects:

> > - Atomically calls `lock.unlock()` and blocks on `*this`.
> > - When unblocked, calls `lock.lock()` (possibly blocking on the lock) and returns.
> > - The function will unblock when signaled by a call to `notify_one()`, a call to `notify_all()`, by the current time exceeding `abs_time` if `Clock::now() >= abs_time`, or spuriously.
> > - If the function exits via an exception, `lock.unlock()` shall be called prior to exiting the function scope.

> > -17- Postcondition: `lock` is locked by the calling thread.

> > -18- Returns: `Clock::now() < abs_time` `cv_status::timeout` if the function unblocked because `abs_time` was reached, otherwise `cv_status::no_timeout`.

> > -19- Throws: `std::system_error` when the effects or postcondition cannot be achieved.

> > -20- Error conditions:

> > - `operation_not_permitted` — if the thread does not own the lock.
> > - equivalent error condition from `lock.lock()` or `lock.unlock()`.

>     template <class Rep, class Period>
>       bool cv_status wait_for(unique_lock<mutex>& lock,
>                     const chrono::duration<Rep, Period>& rel_time);

> > -21- Effects Returns:

> > >     wait_until(lock, chrono::monotonic_clock::now() + rel_time)

> > -22- Returns: `false` if the call is returning because the time duration specified by `rel_time` has elapsed, otherwise `true`.

> > [ This part of the wording may conflict with 859 in detail, but does not do so in spirit. If both issues are accepted, there is a logical merge. ]

>     template <class Clock, class Duration, class Predicate>
>       bool wait_until(unique_lock<mutex>& lock,
>                       const chrono::time_point<Clock, Duration>& abs_time,
>                       Predicate pred);

> > -23- Effects:

> > >     while (!pred())
> > >       if (!wait_until(lock, abs_time) == cv_status::timeout)
> > >         return pred();
> > >     return true;

> > -24- Returns: `pred()`.

> > -25- [Note: The returned value indicates whether the predicate evaluates to `true` regardless of whether the timeout was triggered. — end note].

Change Class condition_variable_any 30.5.2 [thread.condition.condvarany] as indicated:

>     class condition_variable_any {
>     public:
>       ...
>       template <class Lock, class Clock, class Duration>
>         bool cv_status wait_until(Lock& lock,
>                         const chrono::time_point<Clock, Duration>& abs_time);
>       template <class Lock, class Clock, class Duration, class Predicate>
>         bool wait_until(Lock& lock,
>                         const chrono::time_point<Clock, Duration>& abs_time,
>                         Predicate pred);

>       template <class Lock, class Rep, class Period>
>         bool cv_status wait_for(Lock& lock,
>                       const chrono::duration<Rep, Period>& rel_time);
>       template <class Lock, class Rep, class Period, class Predicate>
>         bool wait_for(Lock& lock,
>                       const chrono::duration<Rep, Period>& rel_time,
>                       Predicate pred);
>       ...
>     };

>     ...

>     template <class Lock, class Clock, class Duration>
>       bool cv_status wait_until(Lock& lock,
>                       const chrono::time_point<Clock, Duration>& abs_time);

> > -13- Effects:

> > - Atomically calls `lock.unlock()` and blocks on `*this`.
> > - When unblocked, calls `lock.lock()` (possibly blocking on the lock) and returns.
> > - The function will unblock when signaled by a call to `notify_one()`, a call to `notify_all()`, by the current time exceeding `abs_time` if `Clock::now() >= abs_time`, or spuriously.
> > - If the function exits via an exception, `lock.unlock()` shall be called prior to exiting the function scope.

> > -14- Postcondition: `lock` is locked by the calling thread.

> > -15- Returns: `Clock::now() < abs_time` `cv_status::timeout` if the function unblocked because `abs_time` was reached, otherwise `cv_status::no_timeout`.

> > -16- Throws: `std::system_error` when the effects or postcondition cannot be achieved.

> > -17- Error conditions:

> > - equivalent error condition from `lock.lock()` or `lock.unlock()`.

>     template <class Lock, class Rep, class Period>
>       bool cv_status wait_for(Lock& lock,
>                     const chrono::duration<Rep, Period>& rel_time);

> > -18- Effects Returns:

> > >     wait_until(lock, chrono::monotonic_clock::now() + rel_time)

> > -19- Returns: `false` if the call is returning because the time duration specified by `rel_time` has elapsed, otherwise `true`.

> > [ This part of the wording may conflict with 859 in detail, but does not do so in spirit. If both issues are accepted, there is a logical merge. ]

>     template <class Lock, class Clock, class Duration, class Predicate>
>       bool wait_until(Lock& lock,
>                       const chrono::time_point<Clock, Duration>& rel_time abs_time,
>                       Predicate pred);

> > -20- Effects:

> > >     while (!pred())
> > >       if (!wait_until(lock, abs_time) == cv_status::timeout)
> > >         return pred();
> > >     return true;

> > -21- Returns: `pred()`.

> > -22- [Note: The returned value indicates whether the predicate evaluates to `true` regardless of whether the timeout was triggered. — end note].

### 858. Wording for Minimal Support for Garbage Collection

Section: 20.8.15.6 [util.dynamic.safety] Status: CD1 Submitter: Pete Becker Opened: 2008-06-21 Last modified: 2008-09-26

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Discussion:

The first sentence of the Effects clause for `undeclare_reachable` seems to be missing some words. I can't parse

> ... for all non-null `p` referencing the argument is no longer declared reachable...

I take it the intent is that `undeclare_reachable` should be called only when there has been a corresponding call to `declare_reachable`. In particular, although the wording seems to allow it, I assume that code shouldn't call `declare_reachable` once then call `undeclare_reachable` twice.

I don't know what "shall be live" in the Requires clause means.

In the final Note for `undeclare_reachable`, what does "cannot be deallocated" mean? Is this different from "will not be able to collect"?

For the wording on nesting of `declare_reachable` and `undeclare_reachable`, the words for locking and unlocking recursive mutexes probably are a good model.

[ San Francisco: ]

> Nick: what does "shall be live" mean?

> Hans: I can provide an appropriate cross-reference to the Project Editor to clarify the intent.

Proposed resolution:

In 20.8.15.6 [util.dynamic.safety] (N2670, Minimal Support for Garbage Collection)

Add at the beginning, before paragraph 39

> A complete object is declared reachable while the number of calls to `declare_reachable` with an argument referencing the object exceeds the number of `undeclare_reachable` calls with pointers to the same complete object.

Change paragraph 42 (Requires clause for `undeclare_reachable`)

> If `p` is not null, `declare_reachable(p)` was previously called the complete object referenced by `p` shall have been previously declared reachable, and shall be live (3.8 [basic.life]) from the time of the call until the last `undeclare_reachable(p)` call on the object.

Change the first sentence in paragraph 44 (Effects clause for `undeclare_reachable`):

> Effects: Once the number of calls to `undeclare_reachable(p)` equals the number of calls to `declare_reachable(p)` for all non-null `p` referencing the argument is no longer declared reachable. When this happens, pointers to the object referenced by p may not be subsequently dereferenced. After a call to `undeclare_reachable(p)`, if `p` is not null and the object `q` referenced by `p` is no longer declared reachable, then dereferencing any pointer to `q` that is not safely derived results in undefined behavior. ...

Change the final note:

[Note: It is expected that calls to `declare_reachable(p)` will consume a small amount of memory, in addition to that occupied by the referenced object, until the matching call to `undeclare_reachable(p)` is encountered. In addition, the referenced object cannot be deallocated during this period, and garbage collecting implementations will not be able to collect the object while it is declared reachable. Long running programs should arrange that calls for short-lived objects are matched. --end note]

### 859. Monotonic Clock is Conditionally Supported?

Section: 30.5 [thread.condition] Status: WP Submitter: Pete Becker Opened: 2008-06-23 Last modified: 2009-10-26

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Discussion:

Related to 958, 959.

N2661 says that there is a class named `monotonic_clock`. It also says that this name may be a synonym for `system_clock`, and that it's conditionally supported. So the actual requirement is that it can be monotonic or not, and you can tell by looking at `is_monotonic`, or it might not exist at all (since it's conditionally supported). Okay, maybe too much flexibility, but so be it.

A problem comes up in the threading specification, where several variants of `wait_for` explicitly use `monotonic_clock::now()`. What is the meaning of an effects clause that says

>     wait_until(lock, chrono::monotonic_clock::now() + rel_time)

when `monotonic_clock` is not required to exist?

[ San Francisco: ]

> Nick: maybe instead of saying that chrono::monotonic_clock is conditionally supported, we could say that it's always there, but not necessarily supported..

> Beman: I'd prefer a typedef that identifies the best clock to use for wait_for locks.

> Tom: combine the two concepts; create a duration clock type, but keep the is_monotonic test.

> Howard: if we create a duration_clock type, is it a typedef or an entirely true type?

> There was broad preference for a typedef.

> Move to Open. Howard to provide wording to add a typedef for duration_clock and to replace all uses of monotonic_clock in function calls and signatures with duration_clock.

[ Howard notes post-San Francisco: ]

> After further thought I do not believe that creating a `duration_clock typedef` is the best way to proceed. An implementation may not need to use a `time_point` to implement the `wait_for` functions.

> For example, on POSIX systems `sleep_for` can be implemented in terms of `nanosleep` which takes only a duration in terms of nanoseconds. The current working paper does not describe `sleep_for` in terms of `sleep_until`. And paragraph 2 of 30.2.4 [thread.req.timing] has the words strongly encouraging implementations to use monotonic clocks for `sleep_for`:

> > 2 The member functions whose names end in `_for` take an argument that specifies a relative time. Implementations should use a monotonic clock to measure time for these functions.

> I believe the approach taken in describing the effects of `sleep_for` and `try_lock_for` is also appropriate for `wait_for`. I.e. these are not described in terms of their `_until` variants.

[ 2009-07 Frankfurt: ]

> Beman will send some suggested wording changes to Howard.

> Move to Ready.

[ 2009-07-21 Beman added the requested wording changes to 962. ]

Proposed resolution:

Change 30.5.1 [thread.condition.condvar], p21-22:

>     template <class Rep, class Period>
>       bool wait_for(unique_lock<mutex>& lock,
>                     const chrono::duration<Rep, Period>& rel_time);

> > Precondition: `lock` is locked by the calling thread, and either

> > - no other thread is waiting on this `condition_variable` object or
> > - `lock.mutex()` returns the same value for each of the `lock` arguments supplied by all concurrently waiting threads (via `wait`, `wait_for` or `wait_until`).

> > 21 Effects:

> > >     wait_until(lock, chrono::monotonic_clock::now() + rel_time)

> > - Atomically calls `lock.unlock()` and blocks on `*this`.
> > - When unblocked, calls `lock.lock()` (possibly blocking on the lock) and returns.
> > - The function will unblock when signaled by a call to `notify_one()`, a call to `notify_all()`, by the elapsed time `rel_time` passing (30.2.4 [thread.req.timing]), or spuriously.
> > - If the function exits via an exception, `lock.unlock()` shall be called prior to exiting the function scope.

> > Postcondition: `lock` is locked by the calling thread.

> > 22 Returns: `false` if the call is returning because the time duration specified by `rel_time` has elapsed, otherwise `true`.

> > [ This part of the wording may conflict with 857 in detail, but does not do so in spirit. If both issues are accepted, there is a logical merge. ]

> > Throws: `std::system_error` when the effects or postcondition cannot be achieved.

> > Error conditions:

> > - `operation_not_permitted` -- if the thread does not own the lock.
> > - equivalent error condition from `lock.lock()` or `lock.unlock()`.

Change 30.5.1 [thread.condition.condvar], p26-p29:

>     template <class Rep, class Period, class Predicate>
>       bool wait_for(unique_lock<mutex>& lock,
>                     const chrono::duration<Rep, Period>& rel_time,
>                     Predicate pred);

> > Precondition: `lock` is locked by the calling thread, and either

> > - no other thread is waiting on this `condition_variable` object or
> > - `lock.mutex()` returns the same value for each of the `lock` arguments supplied by all concurrently waiting threads (via `wait`, `wait_for` or `wait_until`).

> > 26 Effects:

> > >     wait_until(lock, chrono::monotonic_clock::now() + rel_time, std::move(pred))

> > > - Executes a loop: Within the loop the function first evaluates `pred()` and exits the loop if the result of `pred()` is `true`.
> > > - Atomically calls `lock.unlock()` and blocks on `*this`.
> > > - When unblocked, calls `lock.lock()` (possibly blocking on the lock).
> > > - The function will unblock when signaled by a call to `notify_one()`, a call to `notify_all()`, by the elapsed time `rel_time` passing (30.1.4 [thread.req.timing]), or spuriously.
> > > - If the function exits via an exception, `lock.unlock()` shall be called prior to exiting the function scope.
> > > - The loop terminates when `pred()` returns `true` or when the time duration specified by `rel_time` has elapsed.

> > 27 [Note: There is no blocking if `pred()` is initially `true`, even if the timeout has already expired. -- end note]

> > Postcondition: `lock` is locked by the calling thread.

> > 28 Returns: `pred()`

> > 29 [Note: The returned value indicates whether the predicate evaluates to `true` regardless of whether the timeout was triggered. -- end note]

> > Throws: `std::system_error` when the effects or postcondition cannot be achieved.

> > Error conditions:

> > - `operation_not_permitted` -- if the thread does not own the lock.
> > - equivalent error condition from `lock.lock()` or `lock.unlock()`.

Change 30.5.2 [thread.condition.condvarany], p18-19:

>     template <class Lock, class Rep, class Period>
>       bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time);

> > 18 Effects:

> > >     wait_until(lock, chrono::monotonic_clock::now() + rel_time)

> > - Atomically calls `lock.unlock()` and blocks on `*this`.
> > - When unblocked, calls `lock.lock()` (possibly blocking on the lock) and returns.
> > - The function will unblock when signaled by a call to `notify_one()`, a call to `notify_all()`, by the elapsed time `rel_time` passing (30.2.4 [thread.req.timing]), or spuriously.
> > - If the function exits via an exception, `lock.unlock()` shall be called prior to exiting the function scope.

> > Postcondition: `lock` is locked by the calling thread.

> > 19 Returns: `false` if the call is returning because the time duration specified by `rel_time` has elapsed, otherwise `true`.

> > Throws: `std::system_error` when the returned value, effects, or postcondition cannot be achieved.

> > Error conditions:

> > - equivalent error condition from `lock.lock()` or `lock.unlock()`.

Change 30.5.2 [thread.condition.condvarany], p23-p26:

>     template <class Lock, class Rep, class Period, class Predicate>
>       bool wait_for(Lock& lock, const chrono::duration<Rep, Period>& rel_time, Predicate pred);

> > Precondition: `lock` is locked by the calling thread, and either

> > - no other thread is waiting on this `condition_variable` object or
> > - `lock.mutex()` returns the same value for each of the `lock` arguments supplied by all concurrently waiting threads (via `wait`, `wait_for` or `wait_until`).

> > 23 Effects:

> > >     wait_until(lock, chrono::monotonic_clock::now() + rel_time, std::move(pred))

> > > - Executes a loop: Within the loop the function first evaluates `pred()` and exits the loop if the result of `pred()` is `true`.
> > > - Atomically calls `lock.unlock()` and blocks on `*this`.
> > > - When unblocked, calls `lock.lock()` (possibly blocking on the lock).
> > > - The function will unblock when signaled by a call to `notify_one()`, a call to `notify_all()`, by the elapsed time `rel_time` passing (30.1.4 [thread.req.timing]), or spuriously.
> > > - If the function exits via an exception, `lock.unlock()` shall be called prior to exiting the function scope.
> > > - The loop terminates when `pred()` returns `true` or when the time duration specified by `rel_time` has elapsed.

> > 24 [Note: There is no blocking if `pred()` is initially `true`, even if the timeout has already expired. -- end note]

> > Postcondition: `lock` is locked by the calling thread.

> > 25 Returns: `pred()`

> > 26 [Note: The returned value indicates whether the predicate evaluates to `true` regardless of whether the timeout was triggered. -- end note]

> > Throws: `std::system_error` when the effects or postcondition cannot be achieved.

> > Error conditions:

> > - `operation_not_permitted` -- if the thread does not own the lock.
> > - equivalent error condition from `lock.lock()` or `lock.unlock()`.

### 866. Qualification of placement new-expressions

Section: 20.8.13 [specialized.algorithms], 20.8.15.2.6 [util.smartptr.shared.create] Status: WP Submitter: Alberto Ganesh Barbati Opened: 2008-07-14 Last modified: 2009-03-09

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Discussion:

LWG issue 402 replaced "`new`" with "`::new`" in the placement new-expression in 20.8.8.1 [allocator.members]. I believe the rationale given in 402 applies also to the following other contexts:

- in 20.8.13 [specialized.algorithms], all four algorithms `unitialized_copy`, `unitialized_copy_n`, `unitialized_fill` and `unitialized_fill_n` use the unqualified placement new-expression in some variation of the form:

  >     new  (static_cast<void*>(&*result)) typename  iterator_traits<ForwardIterator>::value_type(*first);

- in 20.8.15.2.6 [util.smartptr.shared.create] there is a reference to the unqualified placement new-expression:

  >     new  (pv)  T(std::forward<Args>(args)...),

I suggest to add qualification in all those places. As far as I know, these are all the remaining places in the whole library that explicitly use a placement new-expression. Should other uses come out, they should be qualified as well.

As an aside, a qualified placement new-expression does not need additional requirements to be compiled in a constrained context. By adding qualification, the `HasPlacementNew` concept introduced recently in N2677 (Foundational Concepts) would no longer be needed by library and should therefore be removed.

[ San Francisco: ]

> Detlef: If we move this to Ready, it's likely that we'll forget about the side comment about the `HasPlacementNew` concept.

[ post San Francisco: ]

> Daniel: `HasPlacementNew` has been removed from N2774 (Foundational Concepts).

Proposed resolution:

Replace "`new`" with "`::new`" in:

- 20.8.13.2 [uninitialized.copy], paragraphs 1 and 3
- 20.8.13.3 [uninitialized.fill] paragraph 1
- 20.8.13.4 [uninitialized.fill.n] paragraph 1
- 20.8.15.2.6 [util.smartptr.shared.create] once in paragraph 1 and twice in paragraph 2.

### 869. Bucket (local) iterators and iterating past end

Section: 23.2.5 [unord.req] Status: WP Submitter: Sohail Somani Opened: 2008-07-22 Last modified: 2009-07-18

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Discussion:

Is there any language in the current draft specifying the behaviour of the following snippet?

>     unordered_set<int> s;
>     unordered_set<int>::local_iterator it = s.end(0);

>     // Iterate past end - the unspecified part
>     it++;

I don't think there is anything about `s.end(n)` being considered an iterator for the past-the-end value though (I think) it should be.

[ San Francisco: ]

> We believe that this is not a substantive change, but the proposed change to the wording is clearer than what we have now.

[ Post Summit: ]

> Recommend Tentatively Ready.

Proposed resolution:

Change Table 97 "Unordered associative container requirements" in 23.2.5 [unord.req]:

> Table 97: Unordered associative container requirements
> expression | return type | assertion/note pre/post-condition | complexity
> --- | --- | --- | ---
> `b.begin(n)` | `local_iterator` `const_local_iterator` for const `b`. | Pre: n shall be in the range [0,b.bucket_count()). Note: [b.begin(n), b.end(n)) is a valid range containing all of the elements in the nth bucket. `b.begin(n)` returns an iterator referring to the first element in the bucket. If the bucket is empty, then `b.begin(n) == b.end(n)`. | Constant
> `b.end(n)` | `local_iterator` `const_local_iterator` for const `b`. | Pre: n shall be in the range `[0, b.bucket_count())`. `b.end(n)` returns an iterator which is the past-the-end value for the bucket. | Constant

### 876. `basic_string` access operations should give stronger guarantees

Section: 21.4 [basic.string] Status: WP Submitter: Daniel Krügler Opened: 2008-08-22 Last modified: 2009-10-26

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Discussion:

During the Sophia Antipolis meeting it was decided to split-off some parts of the n2647 ("Concurrency modifications for `basic_string`") proposal into a separate issue, because these weren't actually concurrency-related. The here proposed changes refer to the recent update document n2668 and attempt to take advantage of the stricter structural requirements.

Indeed there exists some leeway for more guarantees that would be very useful for programmers, especially if interaction with transactionary or exception-unaware C API code is important. This would also allow compilers to take advantage of more performance optimizations, because more functions can have throw() specifications. This proposal uses the form of "Throws: Nothing" clauses to reach the same effect, because there already exists a different issue in progress to clean-up the current existing "schizophrenia" of the standard in this regard.

Due to earlier support for copy-on-write, we find the following unnecessary limitations for C++0x:

1. Missing no-throw guarantees: `data()` and `c_str()` simply return a pointer to their guts, which is a non-failure operation. This should be spelled out. It is also noteworthy to mention that the same guarantees should also be given by the size query functions, because the combination of pointer to content and the length is typically needed during interaction with low-level API.
2. Missing complexity guarantees: `data()` and `c_str()` simply return a pointer to their guts, which is guaranteed O(1). This should be spelled out.
3. Missing reading access to the terminating character: Only the const overload of `operator[]` allows reading access to the terminator char. For more intuitive usage of strings, reading access to this position should be extended to the non-const case. In contrast to C++03 this reading access should now be homogeneously an lvalue access.

The proposed resolution is split into a main part (A) and a secondary part (B) (earlier called "Adjunct Adjunct Proposal"). (B) extends (A) by also making access to index position size() of the at() overloads a no-throw operation. This was separated, because this part is theoretically observable in specifically designed test programs.

[ San Francisco: ]

> We oppose part 1 of the issue but hope to address `size()` in issue 877.

> We do not support part B. 4 of the issue because of the breaking API change.

> We support part A. 2 of the issue.

> On support part A. 3 of the issue:

> > Pete's broader comment: now that we know that basic_string will be a block of contiguous memory, we should just rewrite its specification with that in mind. The expression of the specification will be simpler and probably more correct as a result.

[ 2009-07 Frankfurt ]

> Move proposed resolution A to Ready.

> [ Howard: Commented out part B. ]

Proposed resolution:

1. 1. In 21.4.4 [string.capacity], just after p. 1 add a new paragraph:

      > Throws: Nothing.

   2. In 21.4.5 [string.access] replace p. 1 by the following 4 paragraghs:

      > Requires: `pos ≤ size()`.

      > Returns: If `pos < size()`, returns `*(begin() + pos)`. Otherwise, returns a reference to a `charT()` that shall not be modified.

      > Throws: Nothing.

      > Complexity: Constant time.

   3. In 21.4.7.1 [string.accessors] replace the now common returns clause of `c_str()` and `data()` by the following three paragraphs:

      > Returns: A pointer `p` such that `p+i == &operator[](i)` for each `i` in `[0, size()]`.

      > Throws: Nothing.

      > Complexity: Constant time.

### 878. `forward_list` preconditions

Section: 23.3.3 [forwardlist] Status: WP Submitter: Martin Sebor Opened: 2008-08-23 Last modified: 2009-07-18

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Discussion:

`forward_list` member functions that take a `forward_list::iterator` (denoted `position` in the function signatures) argument have the following precondition:

> Requires: `position` is dereferenceable or equal to `before_begin()`.

I believe what's actually intended is this:

> Requires: `position` is in the range [`before_begin()`, `end()`).

That is, when it's dereferenceable, `position` must point into `*this`, not just any `forward_list` object.

[ San Francisco: ]

> Robert suggested alternate proposed wording which had large support.

[ Post Summit: ]

> Walter: "position is before_begin() or a dereferenceable": add "is" after the "or"

> With that minor update, Recommend Tentatively Ready.

Proposed resolution:

Change the Requires clauses [forwardlist] , p21, p24, p26, p29, and, 23.3.3.5 [forwardlist.ops], p39, p43, p47 as follows:

> Requires: `position` is `before_begin()` or is a dereferenceable iterator in the range `[begin(), end())` or equal to `before_begin()`. ...

### 881. shared_ptr conversion issue

Section: 20.8.15.2.1 [util.smartptr.shared.const] Status: WP Submitter: Peter Dimov Opened: 2008-08-30 Last modified: 2009-10-26

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Discussion:

We've changed `shared_ptr<Y>` to not convert to `shared_ptr<T>` when `Y*` doesn't convert to `T*` by resolving issue 687. This only fixed the converting copy constructor though. N2351 later added move support, and the converting move constructor is not constrained.

[ San Francisco: ]

> We might be able to move this to NAD, Editorial once shared_ptr is conceptualized, but we want to revisit this issue to make sure.

[ 2009-07 Frankfurt ]

> Moved to Ready.

> This issue now represents the favored format for specifying constrained templates.

Proposed resolution:

We need to change the Requires clause of the move constructor:

>     shared_ptr(shared_ptr&& r);
>     template<class Y> shared_ptr(shared_ptr<Y>&& r);

> > Requires Remarks: For the second constructor `Y*` shall be convertible to `T*`. The second constructor shall not participate in overload resolution unless `Y*` is convertible to `T*`.

in order to actually make the example in 687 compile (it now resolves to the move constructor).

### 882. `duration` non-member arithmetic requirements

Section: 20.9.3.5 [time.duration.nonmember] Status: CD1 Submitter: Howard Hinnant Opened: 2008-09-08 Last modified: 2008-09-26

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Discussion:

N2661 specified the following requirements for the non-member `duration` arithmetic:

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator*(const duration<Rep1, Period>& d, const Rep2& s);

> > Requires: Let `CR` represent the `common_type` of `Rep1` and `Rep2`. Both `Rep1` and `Rep2` shall be implicitly convertible to CR, diagnostic required.

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator*(const Rep1& s, const duration<Rep2, Period>& d);

> > Requires: Let `CR` represent the `common_type` of `Rep1` and `Rep2`. Both `Rep1` and `Rep2` shall be implicitly convertible to `CR`, diagnostic required.

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator/(const duration<Rep1, Period>& d, const Rep2& s);

> > Requires: Let `CR` represent the `common_type` of `Rep1` and `Rep2`. Both `Rep1` and `Rep2` shall be implicitly convertible to `CR`, and `Rep2` shall not be an instantiation of `duration`, diagnostic required.

During transcription into the working paper, the requirements clauses on these three functions was changed to:

> Requires: `CR(Rep1, Rep2)` shall exist. Diagnostic required.

This is a non editorial change with respect to N2661 as user written representations which are used in `duration` need not be implicitly convertible to or from arithmetic types in order to interoperate with `duration`s based on arithmetic types. An explicit conversion will do fine for most expressions as long as there exists a `common_type` specialization relating the user written representation and the arithmetic type. For example:

>     class saturate
>     {
>     public:
>       explicit saturate(long long i);
>       ...
>     };

>     namespace std {

>     template <>
>     struct common_type<saturate, long long>
>     {
>         typedef saturate type;
>     };

>     template <>
>     struct common_type<long long, saturate>
>     {
>         typedef saturate type;
>     };

>     }  // std

>     millisecond ms(3);  // integral-based duration
>     duration<saturate, milli> my_ms = ms;  // ok, even with explicit conversions
>     my_ms = my_ms + ms;                    // ok, even with explicit conversions

However, when dealing with multiplication of a duration and its representation, implicit convertibility is required between the rhs and the lhs's representation for the member `*=` operator:

>     template <class Rep, class Period = ratio<1>>
>     class duration {
>     public:
>        ...
>        duration& operator*=(const rep& rhs);
>        ...
>     };
>     ...
>     ms *= 2;               // ok, 2 is implicitly convertible to long long
>     my_ms *= saturate(2);  // ok, rhs is lhs's representation
>     my_ms *= 2;            // error, 2 is not implicitly convertible to saturate

The last line does not (and should not) compile. And we want non-member multiplication to have the same behavior as member arithmetic:

>     my_ms = my_ms * saturate(2);  // ok, rhs is lhs's representation
>     my_ms = my_ms * 2;            // should be error, 2 is not implicitly convertible to saturate

The requirements clauses of N2661 make the last line an error as expected. However the latest working draft at this time (N2723) allows the last line to compile.

All that being said, there does appear to be an error in these requirements clauses as specified by N2661.

> Requires: ... Both `Rep1` and `Rep2` shall be implicitly convertible to CR, diagnostic required.

It is not necessary for both `Rep`s to be implicitly convertible to the `CR`. It is only necessary for the rhs `Rep` to be implicitly convertible to the `CR`. The `Rep` within the `duration` should be allowed to only be explicitly convertible to the `CR`. The explicit-conversion-requirement is covered under 20.9.3.7 [time.duration.cast].

Proposed resolution:

Change the requirements clauses under 20.9.3.5 [time.duration.nonmember]:

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator*(const duration<Rep1, Period>& d, const Rep2& s);

> > Requires: `CR(Rep1, Rep2)` shall exist. `Rep2` shall be implicitly convertible to `CR(Rep1, Rep2)`. Diagnostic required.

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator*(const Rep1& s, const duration<Rep2, Period>& d);

> > Requires d behavior: `CR(Rep1, Rep2)` shall exist. `Rep1` shall be implicitly convertible to `CR(Rep1, Rep2)`. Diagnostic required.

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator/(const duration<Rep1, Period>& d, const Rep2& s);

> > Requires: `CR(Rep1, Rep2)` shall exist `Rep2` shall be implicitly convertible to `CR(Rep1, Rep2)` and `Rep2` shall not be an instantiation of `duration`. Diagnostic required.

### 883. swap circular definition

Section: 23 [containers] Status: WP Submitter: Alisdair Meredith Opened: 2008-09-10 Last modified: 2009-10-26

View other active issues in [containers].

View all other issues in [containers].

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Discussion:

Note in particular that Table 90 "Container Requirements" gives semantics of `a.swap(b)` as `swap(a,b)`, yet for all containers we define `swap(a,b)` to call `a.swap(b)` - a circular definition.

[ San Francisco: ]

> Robert to propose a resolution along the lines of "Postcondition: "a = b, b = a" This will be a little tricky for the hash containers, since they don't have `operator==`.

[ Post Summit Anthony Williams provided proposed wording. ]

[ 2009-07 Frankfurt ]

> Moved to Ready with minor edits (which have been made).

Proposed resolution:

In table 80 in section 23.2.1 [container.requirements.general], replace the postcondition of `a.swap(b)` with the following:

> Table 80 -- Container requirements
> Expression | Return type | Operational semantics | Assertion/note pre-/post-conidtion | Complexity
> --- | --- | --- | --- | ---
> ... | ... | ... | ... | ...
> `a.swap(b);` | `void` |  | `swap(a,b)` Exchange the contents of `a` and `b`. | (Note A)

Remove the reference to swap from the paragraph following the table.

> Notes: the algorithms `swap()`, `equal()` and `lexicographical_compare()` are defined in Clause 25. ...

### 886. tuple construction

Section: 20.5.2.1 [tuple.cnstr] Status: WP Submitter: Alisdair Meredith Opened: 2008-09-15 Last modified: 2009-10-26

View all other issues in [tuple.cnstr].

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Discussion:

20.5.2.1 [tuple.cnstr]:

> Effects: Default initializes each element.

Could be clarified to state each "non-trivial" element. Otherwise we have a conflict with Core deinfition of default initialization - trivial types do not get initialized (rather than initialization having no effect)

I'm going to punt on this one, because it's not an issue that's related to concepts. I suggest bringing it to Howard's attention on the reflector.

[ San Francisco: ]

> Text in draft doesn't mean anything, changing to "non-trivial" makes it meaningful.

> We prefer "value initializes". Present implementations use value-initialization. Users who don't want value initialization have alternatives.

> Request resolution text from Alisdair.

> This issue relates to Issue 868 default construction and value-initialization.

[ 2009-05-04 Alisdair provided wording and adds: ]

> Note: This IS a change of semantic from TR1, although one the room agreed with during the discussion. To preserve TR1 semantics, this would have been worded:

> >     requires DefaultConstructible<Types>... tuple();

> > > -2- Effects: Default-initializes each non-trivial element.

[ 2009-07 Frankfurt ]

> Move to Ready.

Proposed resolution:

Change p2 in Construction 20.5.2.1 [tuple.cnstr]:

>     requires DefaultConstructible<Types>... tuple();

> > -2- Effects: Default Value-initializes each element.

### 888. this_thread::yield too strong

Section: 30.3.2 [thread.thread.this] Status: WP Submitter: Lawrence Crowl Opened: 2008-09-15 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

I never thought I'd say this, but `this_thread::yield` seems to be too strong in specification. The issue is that some systems distinguish between yielding to another thread in the same process and yielding to another process. Given that the C++ standard only talks about a single program, one can infer that the specification allows yielding only to another thread within the same program. Posix has no facility for that behavior. Can you please file an issue to weaken the wording. Perhaps "Offers the operating system the opportunity to reschedule."

[ Post Summit: ]

> Recommend move to Tentatively Ready.

Proposed resolution:

Change 30.3.2 [thread.thread.this]/3:

>     void this_thread::yield();

> > Effects: Offers the operating system implementation the opportunity to reschedule. another thread.

### 890. Improving `<system_error>` initialization

Section: 19.5.1 [syserr.errcat] Status: WP Submitter: Beman Dawes Opened: 2008-09-14 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

The `static const error_category` objects `generic_category` and `system_category` in header `<system_error>` are currently declared:

>     const error_category& get_generic_category();
>     const error_category& get_system_category();

>     static const error_category& generic_category = get_generic_category();
>     static const error_category& system_category = get_system_category();

This formulation has several problems:

- Implementation details are exposed, since initialization is specified in the interface. This over-constrains implementations without offsetting user benefits. The form of initialization specified may be less than maximally efficient on some platforms.
- Use of the objects is more expensive in terms of number of machine level instructions. See Implementation experience below.
- Depending on the compiler, some cost may be incurred by each translation unit that includes the header, even if the objects are not used. This is a common scenario in user code, since the header is included by other standard library headers. It should be mentioned that at least one compilers is able to optimize this cost away, however.

IO streams uses a somewhat different formulation for iostream_category, but still suffer much the same problems.

The original plan was to eliminate these problems by applying the C++0x `constexpr` feature. See LWG issue 832. However, that approach turned out to be unimplementable, since it would require a `constexpr` object of a class with virtual functions, and that is not allowed by the core language.

The proposed resolution was developed as an alternative. It mitigates the above problems by removing initialization from the visible interface, allowing implementations flexibility.

Implementation experience:

Prototype implementations of the current WP interface and proposed resolution interface were tested with recent Codegear, GCC, Intel, and Microsoft compilers on Windows. The code generated by the Microsoft compiler was studied at length; the WP and proposal versions generated very similar code. For both versions the compiler did make use of static initialization; apparently the compiler applied an implicit `constexpr` where useful, even in cases where `constexpr` would not be permitted by the language!

Acknowledgements:

Martin Sebor, Chris Kohlhoff, and John Lakos provided useful ideas and comments on initialization issues.

[ San Francisco: ]

> Martin: prefers not to create more file-scope static objects, and would like to see `get_*` functions instead.

[Pre-Summit:]

> Beman: The proposed resolution has been reworked to remove the file-scope static objects, per Martin's suggestions. The `get_` prefix has been eliminated from the function names as no longer necessary and to conform with standard library naming practice.

[ Post Summit: ]

> Agreement that this is wise and essential, text provided works and has been implemented. Seems to be widespread consensus. Move to Tentative Ready.

Proposed resolution:

Change 17.6.4.13 [value.error.codes] Value of error codes as indicated:

> Certain functions in the C++ standard library report errors via a `std::error_code` (19.4.2.2) object. That object's `category()` member shall return a reference to `std::system_category```()`` for errors originating from the operating system, or a reference to an implementation-defined error_category object for errors originating elsewhere. The implementation shall define the possible values of value() for each of these error categories. [Example: For operating systems that are based on POSIX, implementations are encouraged to define the `std::system_category```()`` values as identical to the POSIX `errno` values, with additional values as defined by the operating system's documentation. Implementations for operating systems that are not based on POSIX are encouraged to define values identical to the operating system's values. For errors that do not originate from the operating system, the implementation may provide enums for the associated values --end example]

Change 19.5.1.1 [syserr.errcat.overview] Class `error_category` overview `error_category` synopsis as indicated:

>     const error_category& get_generic_category();
>     const error_category& get_system_category();

>     static storage-class-specifier const error_category& generic_category = get_generic_category();
>     static storage-class-specifier const error_category& system_category = get_system_category();

Change 19.5.1.5 [syserr.errcat.objects] Error category objects as indicated:

>     const error_category& get_generic_category();

> > Returns: A reference to an object of a type derived from class `error_category`.

> > Remarks: The object's `default_error_condition` and `equivalent` virtual functions shall behave as specified for the class `error_category`. The object's `name` virtual function shall return a pointer to the string `"GENERIC"`.

>     const error_category& get_system_category();

> > Returns: A reference to an object of a type derived from class `error_category`.

> > Remarks: The object's `equivalent` virtual functions shall behave as specified for class `error_category`. The object's `name` virtual function shall return a pointer to the string `"system"`. The object's `default_error_condition` virtual function shall behave as follows:

> > > If the argument `ev` corresponds to a POSIX `errno` value `posv`, the function shall return `error_condition(posv, generic_category())`. Otherwise, the function shall return `error_condition(ev, system_category())`. What constitutes correspondence for any given operating system is unspecified. [Note: The number of potential system error codes is large and unbounded, and some may not correspond to any POSIX `errno` value. Thus implementations are given latitude in determining correspondence. -- end note]

Change 19.5.2.2 [syserr.errcode.constructors] Class error_code constructors as indicated:

>     error_code();

> > Effects: Constructs an object of type error_code.

> > Postconditions: `val_ == 0` and `cat_ == &system_category``()`.

Change 19.5.2.3 [syserr.errcode.modifiers] Class error_code modifiers as indicated:

>     void clear();

> > Postconditions: `value() == 0` and `category() == system_category``()`.

Change 19.5.2.5 [syserr.errcode.nonmembers] Class error_code non-member functions as indicated:

>     error_code make_error_code(errc e);

> > Returns: `error_code(static_cast<int>(e), generic_category``()``)`.

Change 19.5.3.2 [syserr.errcondition.constructors] Class error_condition constructors as indicated:

>     error_condition();

> > Effects: Constructs an object of type `error_condition`.

> > Postconditions: `val_ == 0` and `cat_ == &generic_category``()`.

Change 19.5.3.3 [syserr.errcondition.modifiers] Class error_condition modifiers as indicated:

>     void clear();

> > Postconditions: `value() == 0` and `category() == generic_category``()`.

Change 19.5.3.5 [syserr.errcondition.nonmembers] Class error_condition non-member functions as indicated:

>     error_condition make_error_condition(errc e);

> > Returns: `error_condition(static_cast<int>(e), generic_category())`.

Change 27.5 [iostreams.base] Iostreams base classes, Header <ios> synopsis as indicated:

>     concept_map ErrorCodeEnum<io_errc> { };
>     error_code make_error_code(io_errc e);
>     error_condition make_error_condition(io_errc e);
>     storage-class-specifier const error_category& iostream_category();

Change 27.5.2.1.1 [ios::failure] Class ios_base::failure, paragraph 2 as indicated:

> When throwing ios_base::failure exceptions, implementations should provide values of ec that identify the specific reason for the failure. [ Note: Errors arising from the operating system would typically be reported as `system_category``()` errors with an error value of the error number reported by the operating system. Errors arising from within the stream library would typically be reported as `error_code(io_errc::stream, iostream_category())`. --end note ]

Change 27.5.5.5 [error.reporting] Error reporting as indicated:

>     error_code make_error_code(io_errc e);

> > Returns: `error_code(static_cast<int>(e), iostream_category`()`)`.

>     error_condition make_error_condition(io_errc e);

> > Returns: `error_condition(static_cast<int>(e), iostream_category`()`)`.

>     storage-class-specifier const error_category& iostream_category();

> > The implementation shall initialize iostream_category. Its storage-class-specifier may be static or extern. It is unspecified whether initialization is static or dynamic (3.6.2). If initialization is dynamic, it shall occur before completion of the dynamic initialization of the first translation unit dynamically initialized that includes header <system_error>.

> > Returns: A reference to an object of a type derived from class `error_category`.

> > Remarks: The object's default_error_condition and equivalent virtual functions shall behave as specified for the class error_category. The object's name virtual function shall return a pointer to the string "iostream".

### 894. longjmp and destructors

Section: 18.10 [support.runtime] Status: WP Submitter: Lawrence Crowl, Alisdair Meredith Opened: 2008-09-17 Last modified: 2009-03-09

View all other issues in [support.runtime].

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Discussion:

The interaction between `longjmp` and exceptions seems unnecessarily restrictive and not in keeping with existing practice.

Proposed resolution:

Edit paragraph 4 of 18.10 [support.runtime] as follows:

> The function signature `longjmp(jmp_buf jbuf, int val)` has more restricted behavior in this International Standard. A `setjmp/longjmp` call pair has undefined behavior if replacing the `setjmp` and `longjmp` by `catch` and `throw` would destroy invoke any non-trivial destructors for any automatic objects.

### 898. Small contradiction in n2723 to forward to committee

Section: 23.3.3.5 [forwardlist.ops] Status: WP Submitter: Arch Robison Opened: 2008-09-08 Last modified: 2009-07-18

View all other issues in [forwardlist.ops].

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Discussion:

I ran across a small contradiction in working draft n2723.

> 23.3.3 [forwardlist]p2: A `forward_list` satisfies all of the requirements of a container (table 90), except that the `size()` member function is not provided.

> 23.3.3.5 [forwardlist.ops]p57: Complexity: At most `size() + x.size() - 1` comparisons.

Presumably 23.3.3.5 [forwardlist.ops]p57 needs to be rephrased to not use `size()`, or note that it is used there only for sake of notational convenience.

[ 2009-03-29 Beman provided proposed wording. ]

[ Batavia (2009-05): ]

> We agree with the proposed resolution.

> Move to Tentatively Ready.

Proposed resolution:

Change 23.3.3.5 [forwardlist.ops], forward_list operations, paragraph 19, merge complexity as indicated:

> Complexity: At most `size() + x.size() distance(begin(), end()) + distance(x.begin(), x.end()) - 1` comparisons.

### 899. Adjusting `shared_ptr` for `nullptr_t`

Section: 20.8.15.2.2 [util.smartptr.shared.dest] Status: WP Submitter: Peter Dimov Opened: 2008-09-18 Last modified: 2009-07-18

View all other issues in [util.smartptr.shared.dest].

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Discussion:

James Dennett, message c++std-lib-22442:

> The wording below addresses one case of this, but opening an issue to address the need to sanity check uses of the term "pointer" in 20.8.15.2 [util.smartptr.shared] would be a good thing.

There's one more reference, in `~shared_ptr;` we can apply your suggested change to it, too. That is:

Change 20.8.15.2.2 [util.smartptr.shared.dest]/1 second bullet from:

> Otherwise, if *this owns a pointer p and a deleter d, d(p) is called.

to:

> Otherwise, if *this owns an object p and a deleter d, d(p) is called.

[ Post Summit: ]

> Recommend Review.

[ Batavia (2009-05): ]

> Peter Dimov notes the analogous change has already been made to "the new nullptr_t taking constructors in 20.8.15.2.1 [util.smartptr.shared.const] p9-13."

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 20.8.15.2.2 [util.smartptr.shared.dest]/1 second bullet:

> - ...
> - Otherwise, if `*this` owns a pointer an object `p` and a deleter `d`, `d(p)` is called.

### 904. result_of argument types

Section: 20.7.4 [func.ret] Status: WP Submitter: Jonathan Wakely Opened: 2008-09-10 Last modified: 2009-07-18

View all other issues in [func.ret].

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Discussion:

The WP and TR1 have the same text regarding the argument types of a `result_of` expression:

> The values `ti` are lvalues when the corresponding type `Ti` is a reference type, and rvalues otherwise.

I read this to mean that this compiles:

>     typedef int (*func)(int&);
>     result_of<func(int&&)>::type i = 0;

even though this doesn't:

>     int f(int&);
>     f( std::move(0) );

Should the text be updated to say "when `Ti` is an lvalue-reference type" or am I missing something?

I later came up with this self-contained example which won't compile, but I think it should:

>     struct X {
>       void operator()(int&);
>       int operator()(int&&);
>     } x;

>     std::result_of< X(int&&) >::type i = x(std::move(0));

[ Post Summit: ]

> Recommend Tentatively Ready.

Proposed resolution:

Change 20.7.4 [func.ret], p1:

> ... The values `ti` are lvalues when the corresponding type `Ti` is an lvalue-reference type, and rvalues otherwise.

### 907. Bitset's immutable element retrieval is inconsistently defined

Section: 20.3.7.2 [bitset.members] Status: WP Submitter: Daniel Krügler Opened: 2008-09-26 Last modified: 2009-07-18

View all other issues in [bitset.members].

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Discussion:

The current standard 14882::2003(E) as well as the current draft N2723 have in common a contradiction of the operational semantics of member function test 20.3.7.2 [bitset.members]/56-58 and the immutable member `operator[]` overload 20.3.7.2 [bitset.members]/64-66 (all references are defined in terms of N2723):

1.     bool test(size_t pos) const;

   > Requires: `pos` is valid

   > Throws: `out_of_range` if `pos` does not correspond to a valid bit position.

   > Returns: `true` if the bit at position `pos` in `*this` has the value one.

2.     constexpr bool operator[](size_t pos) const;

   > Requires: `pos` shall be valid.

   > Throws: nothing.

   > Returns: `test(pos)`.

Three interpretations:

1. The `operator[]` overload is indeed allowed to throw an exception (via `test()`, if `pos` corresponds to an invalid bit position) which does not leave the call frame. In this case this function cannot be a `constexpr` function, because `test()` is not, due to 5.19 [expr.const]/2, last bullet.
2. The intend was not to throw an exception in `test` in case of an invalid bit position. There is only little evidence for this interpretation.
3. The intend was that `operator[]` should not throw any exception, but that `test` has the contract to do so, if the provided bit position is invalid.

The problem became worse, because issue 720 recently voted into WP argued that member `test` logically must be a `constexpr` function, because it was used to define the semantics of another `constexpr` function (the `operator[]` overload).

Three alternatives are proposed, corresponding to the three bullets (A), (B), and (C), the author suggests to follow proposal (C).

Proposed alternatives:

1. Remove the `constexpr` specifier in front of `operator[]` overload and undo that of member `test` (assuming 720 is accepted) in both the class declaration 20.3.7 [template.bitset]/1 and in the member description before 20.3.7.2 [bitset.members]/56 and before /64 to read:

   >     constexpr bool test(size_t pos) const;
   >     ..
   >     constexpr bool operator[](size_t pos) const;

   Change the throws clause of p. 65 to read:

   > Throws: nothing `out_of_range` if `pos` does not correspond to a valid bit position.

2. Replace the throws clause p. 57 to read:

   > Throws: `out_of_range` if `pos` does not correspond to a valid bit position nothing.

3. Undo the addition of the `constexpr` specifier to the `test` member function in both class declaration 20.3.7 [template.bitset]/1 and in the member description before 20.3.7.2 [bitset.members]/56, assuming that 720 was applied.

   >     constexpr bool test(size_t pos) const;

   Change the returns clause p. 66 to read:

   > Returns: `test(pos)` `true` if the bit at position `pos` in `*this` has the value one, otherwise `false`.

[ Post Summit: ]

> Lawrence: proposed resolutions A, B, C are mutually exclusive.

> Recommend Review with option C.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

3. Undo the addition of the `constexpr` specifier to the `test` member function in both class declaration 20.3.7 [template.bitset]/1 and in the member description before 20.3.7.2 [bitset.members]/56, assuming that 720 was applied.

   >     constexpr bool test(size_t pos) const;

   Change the returns clause p. 66 to read:

   > Returns: `test(pos)` `true` if the bit at position `pos` in `*this` has the value one, otherwise `false`.

### 909. `regex_token_iterator` should use `initializer_list`

Section: 28.12.2 [re.tokiter] Status: WP Submitter: Daniel Krügler Opened: 2008-09-26 Last modified: 2009-07-18

View all other issues in [re.tokiter].

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Discussion:

Addresses UK 319

Construction of a `regex_token_iterator` (28.12.2 [re.tokiter]/6+) usually requires the provision of a sequence of integer values, which can currently be done via a `std::vector<int>` or a C array of `int`. Since the introduction of `initializer_list` in the standard it seems much more reasonable to provide a corresponding constructor that accepts an `initializer_list<int>` instead. This could be done as a pure addition or one could even consider replacement. The author suggests the replacement strategy (A), but provides an alternative additive proposal (B) as a fall-back, because of the handiness of this range type:

[ Batavia (2009-05): ]

> We strongly recommend alternative B of the proposed resolution in order that existing code not be broken. With that understanding, move to Tentatively Ready.

Original proposed wording:

1. 1. In 28.12.2 [re.tokiter]/6 and the list 28.12.2.1 [re.tokiter.cnstr]/10-11 change the constructor declaration:

      >     template <std::size_t N>
      >     regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
      >                          const regex_type& re,
      >                          const int (&submatches)[N] initializer_list<int> submatches,
      >                          regex_constants::match_flag_type m =
      >                            regex_constants::match_default);

   2. In 28.12.2.1 [re.tokiter.cnstr]/12 change the last sentence

      > The third constructor initializes the member `subs` to hold a copy of the sequence of integer values pointed to by the iterator range `[&submatches.begin(), &submatches.end() + N)`.

2. 1. In 28.12.2 [re.tokiter]/6 and the list 28.12.2.1 [re.tokiter.cnstr]/10-11 insert the following constructor declaration between the already existing ones accepting a `std::vector` and a C array of `int`, resp.:

      >     regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
      >                          const regex_type& re,
      >                          initializer_list<int> submatches,
      >                          regex_constants::match_flag_type m =
      >                            regex_constants::match_default);

   2. In 28.12.2.1 [re.tokiter.cnstr]/12 change the last sentence

      > The third and fourth constructor initializes the member `subs` to hold a copy of the sequence of integer values pointed to by the iterator range `[&submatches,&submatches + N)` and `[submatches.begin(),submatches.end())`, respectively.

Proposed resolution:

2. 1. In 28.12.2 [re.tokiter]/6 and the list 28.12.2.1 [re.tokiter.cnstr]/10-11 insert the following constructor declaration between the already existing ones accepting a `std::vector` and a C array of `int`, resp.:

      >     regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
      >                          const regex_type& re,
      >                          initializer_list<int> submatches,
      >                          regex_constants::match_flag_type m =
      >                            regex_constants::match_default);

   2. In 28.12.2.1 [re.tokiter.cnstr]/12 change the last sentence

      > The third and fourth constructor initializes the member `subs` to hold a copy of the sequence of integer values pointed to by the iterator range `[&submatches,&submatches + N)` and `[submatches.begin(),submatches.end())`, respectively.

### 922. [func.bind.place] Number of placeholders

Section: B [implimits] Status: WP Submitter: Sohail Somani Opened: 2008-10-11 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

Addresses DE 24

With respect to the section 20.7.11.1.4 [func.bind.place]:

TR1 dropped some suggested implementation quantities for the number of placeholders. The purpose of this defect is to put these back for C++0x.

[ Post Summit: ]

> see DE 24

> Recommend applying the proposed resolution from DE 24, with that Tentatively Ready.

Original proposed resolution:

Add 20.7.11.1.4 [func.bind.place]/2:

> While the exact number of placeholders (`_M`) is implementation defined, this number shall be at least 10.

Proposed resolution:

Add to B [implimits]:

- Number of placeholders (20.7.11.1.4 [func.bind.place]) [10].

### 925. `shared_ptr`'s explicit conversion from `unique_ptr`

Section: 20.8.15.2.1 [util.smartptr.shared.const] Status: WP Submitter: Rodolfo Lima Opened: 2008-10-12 Last modified: 2009-07-18

View all other issues in [util.smartptr.shared.const].

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Discussion:

The current working draft (N2798), section 20.8.15.2.1 [util.smartptr.shared.const] declares `shared_ptr`'s constructor that takes a rvalue reference to `unique_ptr` and `auto_ptr` as being explicit, affecting several valid smart pointer use cases that would take advantage of this conversion being implicit, for example:

>     class A;
>     std::unique_ptr<A> create();
>     void process(std::shared_ptr<A> obj);

>     int main()
>     {
>        process(create());                  // use case #1
>        std::unique_ptr<A> uobj = create();
>        process(std::move(uobj));           // use case #2
>        return 0;
>     }

If `unique_ptr` to `shared_ptr` conversions are explicit, the above lines should be written:

>     process(std::shared_ptr<A>(create()));        // use case #1
>     process(std::shared_ptr<A>(std::move(uobj))); // use case #2

The extra cast required doesn't seems to give any benefits to the user, nor protects him of any unintended conversions, this being the raison d'etre of explicit constructors.

It seems that this constructor was made explicit to mimic the conversion from `auto_ptr` in pre-rvalue reference days, which accepts both lvalue and rvalue references. Although this decision was valid back then, C++0x allows the user to express in a clear and non verbose manner when he wants move semantics to be employed, be it implicitly (use case 1) or explicitly (use case 2).

[ Batavia (2009-05): ]

> Howard and Alisdair like the motivating use cases and the proposed resolution.

> Move to Tentatively Ready.

Proposed resolution:

In both 20.8.15.2 [util.smartptr.shared] paragraph 1 and 20.8.15.2.1 [util.smartptr.shared.const] change:

>     template <class Y> explicit shared_ptr(auto_ptr<Y> &&r);
>     template <class Y, class D> explicit shared_ptr(unique_ptr<Y, D> &&r);

### 931. type trait `extent<T, I>`

Section: 20.6.4.3 [meta.unary.prop] Status: WP Submitter: Yechezkel Mett Opened: 2008-11-04 Last modified: 2009-07-18

View other active issues in [meta.unary.prop].

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Discussion:

The draft (N2798) says in 20.6.4.3 [meta.unary.prop] Table 44:

> Table 44 -- Type property queries
> Template | Value
> --- | ---
> `template <class T, unsigned I = 0> struct extent;` | If `T` is not an array type (8.3.4), or if it has rank less than `I`, or if `I` is 0 and `T` has type "array of unknown bound of `U`", then 0; otherwise, the size of the `I`'th dimension of `T`

Firstly it isn't clear from the wording if `I` is 0-based or 1-based ("the `I`'th dimension" sort of implies 1-based). From the following example it is clear that the intent is 0-based, in which case it should say "or if it has rank less than or equal to `I`".

Sanity check:

The example says `assert((extent<int[2], 1>::value) == 0);`

Here the rank is 1 and `I` is 1, but the desired result is 0.

[ Post Summit: ]

> Do not use "size" or "value", use "bound". Also, move the cross-reference to 8.3.4 to just after "bound".

> Recommend Tentatively Ready.

Proposed resolution:

In Table 44 of 20.6.4.3 [meta.unary.prop], third row, column "Value", change the cell content:

> Table 44 -- Type property queries
> Template | Value
> --- | ---
> `template <class T, unsigned I = 0> struct extent;` | If `T` is not an array type (8.3.4), or if it has rank less than or equal to `I`, or if `I` is 0 and `T` has type "array of unknown bound of `U`", then 0; otherwise, the size bound (8.3.4) of the `I`'th dimension of `T`, where indexing of `I` is zero-based.

[ Wording supplied by Daniel. ]

### 934. `duration` is missing `operator%`

Section: 20.9.3 [time.duration] Status: WP Submitter: Terry Golubiewski Opened: 2008-11-30 Last modified: 2009-10-26

View other active issues in [time.duration].

View all other issues in [time.duration].

View all issues with WP status.

Discussion:

Addresses US 81

`duration` is missing `operator%`. This operator is convenient for computing where in a time frame a given `duration` lies. A motivating example is converting a `duration` into a "broken-down" time duration such as hours::minutes::seconds:

>     class ClockTime
>     {
>         typedef std::chrono::hours hours;
>         typedef std::chrono::minutes minutes;
>         typedef std::chrono::seconds seconds;
>     public:
>         hours hours_;
>         minutes minutes_;
>         seconds seconds_;

>         template <class Rep, class Period>
>           explicit ClockTime(const std::chrono::duration<Rep, Period>& d)
>             : hours_  (std::chrono::duration_cast<hours>  (d)),
>               minutes_(std::chrono::duration_cast<minutes>(d % hours(1))),
>               seconds_(std::chrono::duration_cast<seconds>(d % minutes(1)))
>               {}
>     };

[ Summit: ]

> Agree except that there is a typo in the proposed resolution. The member operators should be operator%=.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

[ 2009-07 Frankfurt ]

> Moved from Tentatively Ready to Open only because the wording needs to be improved for enable_if type constraining, possibly following Robert's formula.

[ 2009-07 Frankfurt: ]

> Howard to open a separate issue (1177) to handle the removal of member functions from overload sets, provide wording, and possibly demonstrate how this can be implemented using enable_if (see 947).

> Move to Ready.

Proposed resolution:

Add to the synopsis in 20.9 [time]:

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator%(const duration<Rep1, Period>& d, const Rep2& s);
>     template <class Rep1, class Period1, class Rep2, class Period2>
>       typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type
>       operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);

Add to the synopsis of `duration` in 20.9.3 [time.duration]:

>     template <class Rep, class Period = ratio<1>>
>     class duration {
>     public:
>       ...
>       duration& operator%=(const rep& rhs);
>       duration& operator%=(const duration& d);
>       ...
>     };

Add to 20.9.3.3 [time.duration.arithmetic]:

>     duration& operator%=(const rep& rhs);

> > Effects: `rep_ %= rhs`.

> > Returns: `*this`.

>     duration& operator%=(const duration& d);

> > Effects: `rep_ %= d.count()`.

> > Returns: `*this`.

Add to 20.9.3.5 [time.duration.nonmember]:

>     template <class Rep1, class Period, class Rep2>
>       duration<typename common_type<Rep1, Rep2>::type, Period>
>       operator%(const duration<Rep1, Period>& d, const Rep2& s);

> > Requires: `Rep2` shall be implicitly convertible to `CR(Rep1, Rep2)` and `Rep2` shall not be an instantiation of `duration`. Diagnostic required.

> > Returns: `duration<CR, Period>(d) %= s`.

>     template <class Rep1, class Period1, class Rep2, class Period2>
>       typename common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type
>       operator%(const duration<Rep1, Period1>& lhs, const duration<Rep2, Period2>& rhs);

> > Returns: `common_type<duration<Rep1, Period1>, duration<Rep2, Period2>>::type(lhs) %= rhs`.

### 938. `default_delete<T[]>::operator()` should only accept `T*`

Section: 20.8.14.1.2 [unique.ptr.dltr.dflt1] Status: WP Submitter: Howard Hinnant Opened: 2008-12-07 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

Consider:

>     derived* p = new derived[3];
>     std::default_delete<base[]> d;
>     d(p);  // should fail

Currently the marked line is a run time failure. We can make it a compile time failure by "poisoning" `op(U*)`.

[ Post Summit: ]

> Recommend Review.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Add to 20.8.14.1.2 [unique.ptr.dltr.dflt1]:

>     namespace std {
>       template <class T> struct default_delete<T[]> {
>         void operator()(T*) const;
>       template <class U> void operator()(U*) const = delete;
>     };
>     }

### 943. `ssize_t` undefined

Section: 29.5.2 [atomics.types.address] Status: WP Submitter: Holger Grund Opened: 2008-12-19 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

There is a row in "Table 122 - Atomics for standard typedef types" in 29.5.1 [atomics.types.integral] with `atomic_ssize_t` and `ssize_t`. Unless, I'm missing something `ssize_t` is not defined by the standard.

[ Summit: ]

> Move to review. Proposed resolution: Remove the typedef. Note: ssize_t is a POSIX type.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Remove the row containing `ssize_t` from Table 119 "Atomics for standard typedef types" in 29.5.2 [atomics.types.address].

### 948. `ratio` arithmetic tweak

Section: 20.4.2 [ratio.arithmetic] Status: WP Submitter: Howard Hinnant Opened: 2008-12-26 Last modified: 2009-07-18

View all other issues in [ratio.arithmetic].

View all issues with WP status.

Discussion:

N2800, 20.4.2 [ratio.arithmetic] lacks a paragraph from the proposal N2661:

> ratio arithmetic [ratio.arithmetic]

> ... If the implementation is unable to form the indicated `ratio` due to overflow, a diagnostic shall be issued.

The lack of a diagnostic on compile-time overflow is a significant lack of functionality. This paragraph could be put back into the WP simply editorially. However in forming this issue I realized that we can do better than that. This paragraph should also allow alternative formulations which go to extra lengths to avoid overflow when possible. I.e. we should not mandate overflow when the implementation can avoid it.

For example:

>     template <class R1, class R2> struct ratio_multiply {
>       typedef see below} type;

> > The nested typedef type shall be a synonym for `ratio<T1, T2>` where `T1` has the value `R1::num * R2::num` and `T2` has the value `R1::den * R2::den`.

Consider the case where `intmax_t` is a 64 bit 2's complement signed integer, and we have:

>     typedef std::ratio<0x7FFFFFFFFFFFFFFF, 0x7FFFFFFFFFFFFFF0> R1;
>     typedef std::ratio<8, 7> R2;
>     typedef std::ratio_multiply<R1, R2>::type RT;

According to the present formulation the implementaiton will multiply `0x7FFFFFFFFFFFFFFF * 8` which will result in an overflow and subsequently require a diagnostic.

However if the implementation is first allowed to divde `0x7FFFFFFFFFFFFFFF` by `7` obtaining `0x1249249249249249 / 1` and divide `8` by `0x7FFFFFFFFFFFFFF0` obtaining `1 / 0x0FFFFFFFFFFFFFFE`, then the exact result can then be computed without overflow:

>     [0x7FFFFFFFFFFFFFFF/0x7FFFFFFFFFFFFFF0] * [8/7] = [0x1249249249249249/0x0FFFFFFFFFFFFFFE]

Example implmentation which accomplishes this:

>     template <class R1, class R2>
>     struct ratio_multiply
>     {
>     private:
>         typedef ratio<R1::num, R2::den> _R3;
>         typedef ratio<R2::num, R1::den> _R4;
>     public:
>         typedef ratio<__ll_mul<_R3::num, _R4::num>::value,
>                       __ll_mul<_R3::den, _R4::den>::value> type;
>     };

[ Post Summit: ]

> Recommend Tentatively Ready.

Proposed resolution:

Add a paragraph prior to p1 in 20.4.2 [ratio.arithmetic]:

> Implementations may use other algorithms to compute the indicated ratios to avoid overflow. If overflow occurs, a diagnostic shall be issued.

### 949. `owner_less`

Section: 20.8.15.3.7 [util.smartptr.ownerless] Status: WP Submitter: Thomas Plum Opened: 2008-12-30 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

20.8.15.3.7 [util.smartptr.ownerless] (class template `owner_less`) says that `operator()(x,y)` shall return `x.before(y)`.

However, `shared_ptr` and `weak_ptr` have an `owner_before()` but not a `before()`, and there's no base class to provide a missing `before()`.

Being that the class is named `owner_less` , I'm guessing that "`before()`" should be "`owner_before()`", right?

[ Herve adds: ]

> Agreed with the typo, it should be "shall return `x.owner_before(y)`".

[ Post Summit: ]

> Recommend Tentatively Ready.

Proposed resolution:

Change 20.8.15.3.7 [util.smartptr.ownerless] p2:

> -2- `operator()(x,y)` shall return `x.owner_before(y)`. [Note: ...

### 965. Various threading bugs #15

Section: 30.5.1 [thread.condition.condvar] Status: WP Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2009-07-18

View other active issues in [thread.condition.condvar].

View all other issues in [thread.condition.condvar].

View all issues with WP status.

Discussion:

30.5.1 [thread.condition.condvar]: the constructor for `condition_variable` throws an exception with error code `device_or_resource_busy` "if attempting to initialize a previously-initialized but as of yet undestroyed `condition_variable`." How can this occur?

[ Summit: ]

> Move to review. Proposed resolution: strike the `device_or_resource_busy` error condition from the constructor of `condition_variable`.

> - This is a POSIX error that cannot occur in this interface because the C++ interface does not separate declaration from initialization.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 30.5.1 [thread.condition.condvar] p3:

> - ...
> - `device_or_resource_busy` -- if attempting to initialize a previously-initialized but as of yet undestroyed `condition_variable`.

### 970. addressof overload unneeded

Section: X [object.addressof] Status: Pending WP Submitter: Howard Hinnant Opened: 2009-01-16 Last modified: 2009-09-25

Discussion:

X [object.addressof] specifies:

>     template <ObjectType T> T* addressof(T& r);
>     template <ObjectType T> T* addressof(T&& r);

The two signatures are ambiguous when the argument is an lvalue. The second signature seems not useful: what does it mean to take the address of an rvalue?

[ Post Summit: ]

> Recommend Review.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change X [object.addressof]:

>     template <ObjectType T> T* addressof(T& r);
>     template <ObjectType T> T* addressof(T&& r);

### 975. `is_convertible` cannot be instantiated for non-convertible types

Section: 20.6.5 [meta.rel] Status: WP Submitter: Daniel Krügler Opened: 2009-01-25 Last modified: 2009-07-18

View all other issues in [meta.rel].

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Discussion:

Addresses UK 206

Related to 1114.

The current specification of `std::is_convertible` (reference is draft N2798) is basically defined by 20.6.5 [meta.rel]/4:

> In order to instantiate the template `is_convertible<From, To>`, the following code shall be well formed:

> >     template <class T>
> >       typename add_rvalue_reference<T>::type create();

> >     To test() {
> >       return create<From>();
> >     }

> [Note: This requirement gives well defined results for reference types, void types, array types, and function types. --end note]

The first sentence can be interpreted, that e.g. the expression

>     std::is_convertible<double, int*>::value

is ill-formed because `std::is_convertible<double, int*>` could not be instantiated, or in more general terms: The wording requires that `std::is_convertible<X, Y>` cannot be instantiated for otherwise valid argument types `X` and `Y` if `X` is not convertible to `Y`.

This semantic is both unpractical and in contradiction to what the last type traits paper N2255 proposed:

> If the following `test` function is well formed code `b` is `true`, else it is `false`.

> >     template <class T>
> >       typename add_rvalue_reference<T>::type create();

> >     To test() {
> >       return create<From>();
> >     }

> [Note: This definition gives well defined results for `reference` types, `void` types, array types, and function types. --end note]

[ Post Summit: ]

> Jens: Checking that code is well-formed and then returning true/false sounds like speculative compilation. John Spicer would really dislike this. Please find another wording suggesting speculative compilation.

> Recommend Open.

[ Post Summit, Howard adds: ]

> John finds the following wording clearer:

> > Template | Condition | Comments
> > --- | --- | ---
> > `template <class From, class To> struct is_convertible;` | see below | `From` and `To` shall be complete types, arrays of unknown bound, or (possibly cv-qualified) `void` types.

> > Given the following function prototype:

> > >     template <class T>
> > >       typename add_rvalue_reference<T>::type create();

> > `is_convertible<From, To>::value` shall be `true` if the return expression in the following code would be well-formed, including any implicit conversions to the return type of the function, else `is_convertible<From, To>::value` shall be `false`.

> > >     To test() {
> > >       return create<From>();
> > >     }

Original proposed wording:

In 20.6.5 [meta.rel]/4 change:

> In order to instantiate the template `is_convertible<From, To>`, the following code shall be well formed If the following code is well formed `is_convertible<From, To>::value` is `true`, otherwise `false`:[..]

Revision 2

> In 20.6.5 [meta.rel] change:

> > Template | Condition | Comments
> > --- | --- | ---
> > ... | ... | ...
> > `template <class From, class To> struct is_convertible;` | The code set out below shall be well formed. see below | `From` and `To` shall be complete types, arrays of unknown bound, or (possibly cv-qualified) `void` types.

> > -4- In order to instantiate the template `is_convertible<From, To>`, the following code shall be well formed: Given the following function prototype:

> > >     template <class T>
> > >       typename add_rvalue_reference<T>::type create();

> > `is_convertible<From, To>::value` inherits either directly or indirectly from `true_type` if the return expression in the following code would be well-formed, including any implicit conversions to the return type of the function, else `is_convertible<From, To>::value` inherits either directly or indirectly from `false_type`.

> > >     To test() {
> > >       return create<From>();
> > >     }

> > [Note: This requirement gives well defined results for reference types, void types, array types, and function types. -- end note]

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

In 20.6.5 [meta.rel] change:

> Template | Condition | Comments
> --- | --- | ---
> ... | ... | ...
> `template <class From, class To> struct is_convertible;` | The code set out below shall be well formed. see below | `From` and `To` shall be complete types, arrays of unknown bound, or (possibly cv-qualified) `void` types.

> -4- In order to instantiate the template `is_convertible<From, To>`, the following code shall be well formed: Given the following function prototype:

> >     template <class T>
> >       typename add_rvalue_reference<T>::type create();

> the predicate condition for a template specialization `is_convertible<From, To>` shall be satisfied, if and only if the return expression in the following code would be well-formed, including any implicit conversions to the return type of the function.

> >     To test() {
> >       return create<From>();
> >     }

> [Note: This requirement gives well defined results for reference types, void types, array types, and function types. — end note]

### 981. Unordered container requirements should add `initializer_list` support

Section: 23.2.5 [unord.req] Status: WP Submitter: Daniel Krügler Opened: 2009-02-08 Last modified: 2009-07-18

View other active issues in [unord.req].

View all other issues in [unord.req].

View all issues with WP status.

Discussion:

Refering to N2800 all container requirements tables (including those for associative containers) provide useful member function overloads accepting `std::initializer_list` as argument, the only exception is Table 87. There seems to be no reason for not providing them, because 23.5 [unord] is already `initializer_list`-aware. For the sake of library interface consistency and user-expectations corresponding overloads should be added to the table requirements of unordered containers as well.

[ Batavia (2009-05): ]

> We agree with the proposed resolution.

> Move to Tentatively Ready.

Proposed resolution:

In 23.2.5 [unord.req]/9 insert:

> ... `[q1, q2)` is a valid range in `a`, `il` designates an object of type `initializer_list<value_type>`, `t` is a value of type `X::value_type`, ...

In 23.2.5 [unord.req], Table 87 insert:

> Table 87 - Unordered associative container requirements (in addition to container)
> Expression | Return type | Assertion/note pre-/post-condition | Complexity
> --- | --- | --- | ---
> `X(i, j) X a(i, j)` | `X` | ... | ...
> `X(il)` | `X` | Same as `X(il.begin(), il.end())`. | Same as `X(il.begin(), il.end())`.
> ... | ... | ... | ...
> `a = b` | `X` | ... | ...
> `a = il` | `X&` | `a = X(il); return *this;` | Same as `a = X(il)`.
> ... | ... | ... | ...
> `a.insert(i, j)` | `void` | ... | ...
> `a.insert(il)` | `void` | Same as `a.insert(il.begin(), il.end())`. | Same as `a.insert(il.begin(), il.end())`.

### 982. Wrong complexity for initializer_list assignment in Table 85

Section: 23.2.4 [associative.reqmts] Status: WP Submitter: Daniel Krügler Opened: 2009-02-08 Last modified: 2009-07-18

View other active issues in [associative.reqmts].

View all other issues in [associative.reqmts].

View all issues with WP status.

Discussion:

According to N2800, the associative container requirements table 85 says that assigning an `initializer_list` to such a container is of constant complexity, which is obviously wrong.

[ Batavia (2009-05): ]

> We agree with the proposed resolution.

> Move to Tentatively Ready.

Proposed resolution:

In 23.2.4 [associative.reqmts], Table 85 change:

> Table 85 - Associative container requirements (in addition to container)
> Expression | Return type | Assertion/note pre-/post-condition | Complexity
> --- | --- | --- | ---
> `a = il` | `X&` | `a = X(il); return *this;` | constant Same as `a = X(il)`.

### 984. Does `<cinttypes>` have macro guards?

Section: 27.9.2 [c.files] Status: WP Submitter: Howard Hinnant Opened: 2009-02-12 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

The C standard says about `<inttypes.h>`:

> C++ implementations should define these macros only when `__STDC_FORMAT_MACROS`is defined before `<inttypes.h>` is included.

The C standard has a similar note about `<stdint.h>`. For `<cstdint>` we adopted a "thanks but no thanks" policy and documented that fact in 18.4.1 [cstdint.syn]:

> ... [Note: The macros defined by `<stdint>` are provided unconditionally. In particular, the symbols `__STDC_LIMIT_MACROS` and `__STDC_CONSTANT_MACROS` (mentioned in C99 footnotes 219, 220, and 222) play no role in C++. -- end note]

I recommend we put a similar note in 27.9.2 [c.files] regarding `<cinttypes>`.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Add to 27.9.2 [c.files]:

> Table 112 describes header `<cinttypes>`. [Note: The macros defined by `<cintypes>` are provided unconditionally. In particular, the symbol `__STDC_FORMAT_MACROS` (mentioned in C99 footnote 182) plays no role in C++. -- end note]

### 986. Generic `try_lock` contradiction

Section: 30.4.4 [thread.lock.algorithm] Status: WP Submitter: Chris Fairles Opened: 2009-02-14 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

In 30.4.4 [thread.lock.algorithm], the generic `try_lock` effects (p2) say that a failed `try_lock` is when it either returns `false` or throws an exception. In the event a call to `try_lock` does fail, by either returning `false` or throwing an exception, it states that `unlock` shall be called for all prior arguments. Then the returns clause (p3) goes on to state in a note that after returning, either all locks are locked or none will be. So what happens if multiple locks fail on `try_lock`?

Example:

>     #include <mutex>

>     int main() {
>      std::mutex m0, m1, m2;
>      std::unique_lock<std::mutex> l0(m0, std::defer_lock);
>      std::unique_lock<std::mutex> l1(m1); //throws on try_lock
>      std::unique_lock<std::mutex> l2(m2); //throws on try_lock

>      int result = std::try_lock(l0, l1, l2);

>      assert( !l0.owns_lock() );
>      assert( l1.owns_lock() ); //??
>      assert( l2.owns_lock() ); //??
>     }

The first lock's `try_lock` succeeded but, being a prior argument to a lock whose `try_lock` failed, it gets unlocked as per the effects clause of 30.4.4 [thread.lock.algorithm]. However, 2 locks remain locked in this case but the return clause states that either all arguments shall be locked or none will be. This seems to be a contradiction unless the intent is for implementations to make an effort to unlock not only prior arguments, but the one that failed and those that come after as well. Shouldn't the note only apply to the arguments that were successfully locked?

Further discussion and possible resolutions in c++std-lib-23049.

[ Summit: ]

> Move to review. Agree with proposed resolution.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 30.4.4 [thread.lock.algorithm], p2:

> -2- Effects: Calls `try_lock()` for each argument in order beginning with the first until all arguments have been processed or a call to `try_lock()` fails, either by returning `false` or by throwing an exception. If a call to `try_lock()` fails, `unlock()` shall be called for all prior arguments and there shall be no further calls to `try_lock()`.

Delete the note from 30.4.4 [thread.lock.algorithm], p3

> -3- Returns: -1 if all calls to `try_lock()` returned `true`, otherwise a 0-based index value that indicates the argument for which `try_lock()` returned `false`. [Note: On return, either all arguments will be locked or none will be locked. -- end note]

### 990. `monotonic_clock::is_monotonic` must be `true`

Section: 20.9.5.2 [time.clock.monotonic] Status: WP Submitter: Howard Hinnant Opened: 2009-03-09 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

There is some confusion over what the value of `monotonic_clock::is_monotonic` when `monotonic_clock` is a synonym for `system_clock`. The intent is that if `monotonic_clock` exists, then `monotonic_clock::is_monotonic` is `true`.

[ Batavia (2009-05): ]

> We agree with the proposed resolution.

> Move to Tentatively Ready.

Proposed resolution:

Change 20.9.5.2 [time.clock.monotonic], p1:

> -1- Objects of class `monotonic_clock` represent clocks for which values of `time_point` never decrease as physical time advances. `monotonic_clock` may be a synonym for `system_clock` if and only if `system_clock::is_monotonic` is `true`.

### 991. Response to JP 50

Section: 22.3.3.2.2 [conversions.string] Status: WP Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2009-07-18

View all other issues in [conversions.string].

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Discussion:

Add custom allocator parameter to `wstring_convert`, since we cannot allocate memory for strings from a custom allocator.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 22.3.3.2.2 [conversions.string]:

>     template<class Codecvt, class Elem = wchar_t,
>              class Wide_alloc = std::allocator<Elem>,
>              class Byte_alloc = std::allocator<char> > class wstring_convert {
>       public:
>         typedef std::basic_string<char, char_traits<char>, Byte_alloc> byte_string;
>         typedef std::basic_string<Elem, char_traits<Elem>, Wide_alloc> wide_string;
>          ...

Change 22.3.3.2.2 [conversions.string], p3:

> -3- The class template describes an ob ject that controls conversions between wide string ob jects of class `std::basic_string<Elem, char_traits<Elem>, Wide_alloc>` and byte string objects of class `std::basic_string<char, char_traits<char>, Byte_alloc>` (also known as `std::string`).

### 993. Response to UK 188

Section: 18.5 [support.start.term] Status: WP Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2009-07-18

View all other issues in [support.start.term].

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Discussion:

The function `_Exit` does not appear to be defined in this standard. Should it be added to the table of functions included-by-reference to the C standard?

[ 2009-05-09 Alisdair fixed some minor issues in the wording. ]

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Add to 18.5 [support.start.term] Table 20 (Header `<cstdlib>` synopsis) Functions:

>     _Exit

Add before the description of `abort(void)`:

>     void _Exit [[noreturn]] (int status)

> > The function `_Exit(int status)` has additional behavior in this International Standard:

> > - The program is terminated without executing destructors for objects of automatic, thread, or static storage duration and without calling the functions passed to `atexit()` (3.6.3 [basic.start.term]).

### 994. Response to UK 193

Section: 18.6.2.3 [new.handler] Status: WP Submitter: P.J. Plauger Opened: 2009-03-03 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

`quick_exit` has been added as a new valid way to terminate a program in a well defined way

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 18.6.2.3 [new.handler], p2:

> -2- Required behavior: ...

> - ...
> - call either `abort()` or `exit();` terminate execution of the program without returning to the caller

### 997. Response to UK 163

Section: 17.5.1.4 [structure.specifications] Status: WP Submitter: Thomas Plum Opened: 2009-03-03 Last modified: 2009-07-18

View all other issues in [structure.specifications].

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Discussion:

Many functions are defined as "Effects: Equivalent to a...", which seems to also define the preconditions, effects, etc. But this is not made clear.

After studying the occurrences of "Effects: Equivalent to", I agree with the diagnosis but disagree with the solution. In 21.4.2 [string.cons] we find

> 14 Effects: If `InputIterator` is an integral type, equivalent to `basic_string(static_cast<size_type>(begin), static_cast<value_type>(end), a)`

> 15 Otherwise constructs a string from the values in the range `[begin, end)`, as indicated in the Sequence Requirements table (see 23.1.3).

This would be devishly difficult to re-write with an explicit "Equivalent to:" clause. Instead, I propose the following, which will result in much less editorial re-work.

[ 2009-05-09 Alisdair adds: ]

> This issue is related to 492.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Add a new paragraph after 17.5.1.4 [structure.specifications], p3:

> -3- Descriptions of function semantics contain the following elements (as appropriate):154

> - Requires: the preconditions for calling the function
> - Effects: the actions performed by the function
> - Postconditions: the observable results established by the function
> - Returns: a description of the value(s) returned by the function
> - Throws: any exceptions thrown by the function, and the conditions that would cause the exception
> - Complexity: the time and/or space complexity of the function
> - Remarks: additional semantic constraints on the function
> - Error conditions: the error conditions for error codes reported by the function.
> - Notes: non-normative comments about the function

> Whenever the Effects element specifies that the semantics of some function `F` are Equivalent to some code-sequence, then the various elements are interpreted as follows. If `F`'s semantics specifies a Requires element, then that requirement is logically imposed prior to the equivalent-to semantics. Then, the semantics of the code-sequence are determined by the Requires, Effects, Postconditions, Returns, Throws, Complexity, Remarks, Error Conditions and Notes specified for the (one or more) function invocations contained in the code-sequence. The value returned from `F` is specified by `F`'s Returns element, or if `F` has no Returns element, a non-`void` return from `F` is specified by the Returns elements in code-sequence. If `F`'s semantics contains a Throws (or Postconditions, or Complexity) element, then that supersedes any occurrences of that element in the code-sequence.

### 998. Smart pointer referencing its owner

Section: 20.8.14.2.5 [unique.ptr.single.modifiers] Status: WP Submitter: Pavel Minaev Opened: 2009-02-26 Last modified: 2009-07-18

View all other issues in [unique.ptr.single.modifiers].

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Discussion:

Consider the following (simplified) implementation of `std::auto_ptr<T>::reset()`:

>     void reset(T* newptr = 0) {
>        if (this->ptr && this->ptr != newptr) {
>          delete this->ptr;
>        }
>        this->ptr = newptr;
>     }

Now consider the following code which uses the above implementation:

>     struct foo {
>        std::auto_ptr<foo> ap;
>        foo() : ap(this) {}
>        void reset() { ap.reset(); }
>     };
>     int main() {
>        (new foo)->reset();
>     }

With the above implementation of auto_ptr, this results in U.B. at the point of auto_ptr::reset(). If this isn't obvious yet, let me explain how this goes step by step:

1. `foo::reset()` entered
2. `auto_ptr::reset()` entered
3. `auto_ptr::reset()` tries to delete `foo`
4. `foo::~foo()` entered, tries to destruct its members
5. `auto_ptr::~auto_ptr()` executed - `auto_ptr` is no longer a valid object!
6. `foo::~foo()` left
7. `auto_ptr::reset()` sets its "ptr" field to 0 <- U.B.! `auto_ptr` is not a valid object here already!

[ Thanks to Peter Dimov who recognized the connection to `unique_ptr` and brought this to the attention of the LWG, and helped with the solution. ]

[ Howard adds: ]

> To fix this behavior `reset` must be specified such that deleting the pointer is the last action to be taken within `reset`.

[ Alisdair adds: ]

> The example providing the rationale for LWG 998 is poor, as it relies on broken semantics of having two object believing they are unique owners of a single resource. It should not be surprising that UB results from such code, and I feel no need to go out of our way to support such behaviour.

> If an example is presented that does not imply multiple ownership of a unique resource, I would be much more ready to accept the proposed resolution.

[ Batavia (2009-05): ]

> Howard summarizes:

> > This issue has to do with circular ownership, and affects `auto_ptr`, too (but we don't really care about that). It is intended to spell out the order in which operations must be performed so as to avoid the possibility of undefined behavior in the self-referential case.

> Howard points to message c++std-lib-23175 for another example, requested by Alisdair.

> We agree with the issue and with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 20.8.14.2.5 [unique.ptr.single.modifiers], p5 (Effects clause for `reset`), and p6:

> -5- Effects: If `get() == nullptr` there are no effects. Otherwise `get_deleter()(get())`. Assigns `p` to the stored `pointer`, and then if the old value of the `pointer` is not equal to `nullptr`, calls `get_deleter()(`the old value of the `pointer)`. [Note: The order of these operations is significant because the call to `get_deleter()` may destroy `*this`. -- end note]

> -6- Postconditions: `get() == p`. [Note: The postcondition does not hold if the call to `get_deleter()` destroys `*this` since `this->get()` is no longer a valid expression. -- end note]

### 1004. Response to UK 179

Section: 17.6.3.8 [res.on.functions] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-10-26

View all other issues in [res.on.functions].

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Discussion:

Addresses UK 179

According to the 4th bullet there is a problem if "if any replacement function or handler function or destructor operation throws an exception". There should be no problem throwing exceptions so long as they are caught within the function.

[ Batavia (2009-05): ]

> The phrasing "throws an exception" is commonly used elsewhere to mean "throws or propagates an exception." Move to Open pending a possible more general resolution.

[ 2009-07 Frankfurt: ]

> Replace "propagates" in the proposed resolution with the phrase "exits via" and move to Ready.

Proposed resolution:

Change the 4th bullet of 17.6.3.8 [res.on.functions], p2:

> - if any replacement function or handler function or destructor operation throws exits via an exception, unless specifically allowed in the applicable Required behavior: paragraph.

### 1006. `operator delete` in garbage collected implementation

Section: 18.6.1 [new.delete] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-18

View all other issues in [new.delete].

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Discussion:

Addresses UK 190

It is not entirely clear how the current specification acts in the presence of a garbage collected implementation.

[ Summit: ]

> Agreed.

[ 2009-05-09 Alisdair adds: ]

> Proposed wording is too strict for implementations that do not support garbage collection. Updated wording supplied.

[ Batavia (2009-05): ]

> We recommend advancing this to Tentatively Ready with the understanding that it will not be moved for adoption unless and until the proposed resolution to Core issue #853 is adopted.

Proposed resolution:

(Editorial note: This wording ties into the proposed resolution for Core #853)

Add paragraphs to 18.6.1.1 [new.delete.single]:

>     void operator delete(void* ptr) throw();
>     void operator delete(void* ptr, const std::nothrow_t&) throw();

> [ The second signature deletion above is editorial. ]

> > Requires: If an implementation has strict pointer safety (3.7.4.3 [basic.stc.dynamic.safety]) then `ptr` shall be a safely-derived pointer.

> > -10- ...

>     void operator delete(void* ptr, const std::nothrow_t&) throw();

> > Requires: If an implementation has strict pointer safety (3.7.4.3 [basic.stc.dynamic.safety]) then `ptr` shall be a safely-derived pointer.

> > -15- ...

Add paragraphs to 18.6.1.2 [new.delete.array]:

>     void operator delete[](void* ptr) throw();
>     void operator delete[](void* ptr, const std::nothrow_t&) throw();

> [ The second signature deletion above is editorial. ]

> > Requires: If an implementation has strict pointer safety (3.7.4.3 [basic.stc.dynamic.safety]) then `ptr` shall be a safely-derived pointer.

> > -9- ...

>     void operator delete[](void* ptr, const std::nothrow_t&) throw();

> > Requires: If an implementation has strict pointer safety (3.7.4.3 [basic.stc.dynamic.safety]) then `ptr` shall be a safely-derived pointer.

> > -13- ...

Add paragraphs to 18.6.1.3 [new.delete.placement]:

>     void operator delete(void* ptr, void*) throw();

> > Requires: If an implementation has strict pointer safety (3.7.4.3 [basic.stc.dynamic.safety]) then `ptr` shall be a safely-derived pointer.

> > -7- ...

>     void operator delete[](void* ptr, void*) throw();

> > Requires: If an implementation has strict pointer safety (3.7.4.3 [basic.stc.dynamic.safety]) then `ptr` shall be a safely-derived pointer.

> > -9- ...

### 1012. `reverse_iterator` default ctor should value initialize

Section: 24.5.1.3.1 [reverse.iter.cons] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-10-26

View all issues with WP status.

Discussion:

Addresses UK 277

The default constructor default-initializes current, rather than value-initializes. This means that when Iterator corresponds to a trivial type, the current member is left un-initialized, even when the user explictly requests value intialization! At this point, it is not safe to perform any operations on the reverse_iterator other than assign it a new value or destroy it. Note that this does correspond to the basic definition of a singular iterator.

[ Summit: ]

> Agree with option i.

Related issue: 408

[ Batavia (2009-05): ]

> We believe this should be revisited in conjunction with issue 408, which nearly duplicates this issue. Move to Open.

[ 2009-07 post-Frankfurt: ]

> Change "constructed" to "initialized" in two places in the proposed resolution.

> Move to Tentatively Ready.

[ 2009 Santa Cruz: ]

> Moved to Ready for this meeting.

Proposed resolution:

Change [reverse.iter.con]:

>     reverse_iterator();

> > -1- Effects: Default Value initializes `current`. Iterator operations applied to the resulting iterator have defined behavior if and only if the corresponding operations are defined on a default constructed value initialized iterator of type `Iterator`.

Change 24.5.3.3.1 [move.iter.op.const]:

>     move_iterator();

> > -1- Effects: Constructs a `move_iterator`, default value initializing `current`. Iterator operations applied to the resulting iterator have defined behavior if and only if the corresponding operations are defined on a value initialized iterator of type `Iterator`.

### 1014. Response to UK 317 and JP 74

Section: 28.8.2 [re.regex.construct] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-18

View all other issues in [re.regex.construct].

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Discussion:

Addresses UK 317 and JP 74

UK 317:

> `basic_string` has both a constructor and an assignment operator that accepts an initializer list, `basic_regex` should have the same.

JP 74:

> `basic_regx & operator= (initializer_list<T>);` is not defined.

[ Batavia (2009-05): ]

> UK 317 asks for both assignment and constructor, but the requested constructor is already present in the current Working Paper. We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 28.8 [re.regex]:

>     template <class charT,
>               class traits = regex_traits<charT> >
>     class basic_regex {
>       ...
>       basic_regex& operator=(const charT* ptr);
>       basic_regex& operator=(initializer_list<charT> il);
>       template <class ST, class SA>
>         basic_regex& operator=(const basic_string<charT, ST, SA>& p);
>       ...
>     };

Add in 28.8.2 [re.regex.construct]:

> > -20- ...

>     basic_regex& operator=(initializer_list<charT> il);

> > -21- Effects: returns `assign(il.begin(), il.end());`

### 1019. Response to UK 205

Section: 20.6.3 [meta.help] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-10-26

View all other issues in [meta.help].

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Discussion:

Addresses UK 205

`integral_constant` objects should be usable in integral-constant-expressions. The addition to the language of literal types and the enhanced rules for constant expressions make this possible.

[ Batavia (2009-05): ]

> We agree that the `static` data member ought be declared `constexpr`, but do not see a need for the proposed `operator value_type()`. (A use case would be helpful.) Move to Open.

[ 2009-05-23 Alisdair adds: ]

> The motivating case in my mind is that we can then use `true_type` and `false_type` as integral Boolean expressions, for example inside a `static_assert` declaration. In that sense it is purely a matter of style.

> Note that Boost has applied the non-explicit conversion operator for many years as it has valuable properties for extension into other metaprogramming libraries, such as MPL. If additional rationale is desired I will poll the Boost lists for why this extension was originally applied. I would argue that explicit conversion is more appropriate for 0x though.

[ 2009-07-04 Howard adds: ]

> Here's a use case which demonstrates the syntactic niceness which Alisdair describes:

> >     #define requires(...) class = typename std::enable_if<(__VA_ARGS__)>::type

> >     template <class T, class U,
> >         requires(!is_lvalue_reference<T>() ||
> >                   is_lvalue_reference<T>() && is_lvalue_reference<U>()),
> >         requires(is_same<typename base_type<T>::type,
> >                          typename base_type<U>::type>)>
> >     inline
> >     T&&
> >     forward(U&& t)
> >     {
> >         return static_cast<T&&>(t);
> >     }

[ 2009-07 post-Frankfurt: ]

> Move to Tentatively Ready.

[ 2009 Santa Cruz: ]

> Moved to Ready for this meeting.

Proposed resolution:

Add to the `integral_constant` struct definition in 20.6.3 [meta.help]:

>     template <class T, T v>
>     struct integral_constant {
>       static constexpr T value = v;
>       typedef T value_type;
>       typedef integral_constant<T,v> type;
>       constexpr operator value_type() { return value; }
>     };

### 1021. Response to UK 211

Section: 20.8.14.2.3 [unique.ptr.single.asgn] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-11 Last modified: 2009-07-18

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Discussion:

Addresses UK 211

The `nullptr_t` type was introduced to resolve the null pointer literal problem. It should be used for the assignemnt operator, as with the constructor and elsewhere through the library.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change the synopsis in 20.8.14.2 [unique.ptr.single]:

>     unique_ptr& operator=(unspecified-pointer-type nullptr_t);

Change 20.8.14.2.3 [unique.ptr.single.asgn]:

>     unique_ptr& operator=(unspecified-pointer-type nullptr_t);

> > Assigns from the literal 0 or `NULL`. [Note: The unspecified-pointer-type is often implemented as a pointer to a private data member, avoiding many of the implicit conversion pitfalls. -- end note]

### 1037. Response to UK 232

Section: 23.2.3 [sequence.reqmts] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-18

View other active issues in [sequence.reqmts].

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Discussion:

Addresses UK 232

`match_results` may follow the requirements but is not listed a general purpose library container.

Remove reference to `match_results` against `a[n]` operation.

[ Summit: ]

> Agree. `operator[]` is defined elsewhere.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

In 23.2.3 [sequence.reqmts] Table 84, remove reference to `match_results` in the row describing the `a[n]` operation.

### 1038. Response to UK 233

Section: 23.2.3 [sequence.reqmts] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-18

View other active issues in [sequence.reqmts].

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Discussion:

Addresses UK 233

Table 84 is missing references to several new container types.

[ Summit: ]

> Agree.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

In 23.2.3 [sequence.reqmts] Table 84, Add reference to listed containers to the following rows:

> Table 84 -- Optional sequence container operations
> Expression | Return type | Operational semantics | Container
> --- | --- | --- | ---
> `a.front()` | ... | ... | `vector, list, deque, basic_string, array, forward_list`
> `a.back()` | ... | ... | `vector, list, deque, basic_string, array`
> `a.emplace_front(args)` | ... | ... | `list, deque, forward_list`
> `a.push_front(t)` | ... | ... | `list, deque, forward_list`
> `a.push_front(rv)` | ... | ... | `list, deque, forward_list`
> `a.pop_front()` | ... | ... | `list, deque, forward_list`
> `a[n]` | ... | ... | `vector, deque, basic_string, array`
> `a.at(n)` | ... | ... | `vector, deque, basic_string, array`

### 1039. Response to UK 234

Section: 23.2.3 [sequence.reqmts] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-18

View other active issues in [sequence.reqmts].

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Discussion:

Addresses UK 234

The reference to `iterator` in semantics for `back` should also allow for `const_iterator` when called on a const-qualified container. This would be ugly to specify in the 03 standard, but is quite easy with the addition of `auto` in this new standard.

[ Summit: ]

> Agree.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

In 23.2.3 [sequence.reqmts] Table 84, replace iterator with auto in semantics for back:

> Table 84 -- Optional sequence container operations
> Expression | Return type | Operational semantics | Container
> --- | --- | --- | ---
> `a.back()` | `reference; const_reference` for constant `a` | `{ iterator auto tmp = a.end(); --tmp; return *tmp; }` | `vector, list, deque, basic_string`

### 1040. Response to UK 238

Section: 23.2.4 [associative.reqmts] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-18

View other active issues in [associative.reqmts].

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Discussion:

Addresses UK 238

Leaving it unspecified whether or not `iterator` and `const_iterator` are the same type is dangerous, as user code may or may not violate the One Definition Rule by providing overloads for both types. It is probably too late to specify a single behaviour, but implementors should document what to expect. Observing that problems can be avoided by users restricting themselves to using `const_iterator`, add a note to that effect.

Suggest Change 'unspecified' to 'implementation defined'.

[ Summit: ]

> Agree with issue. Agree with adding the note but not with changing the normative text. We believe the note provides sufficient guidance.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

In 23.2.4 [associative.reqmts] p6, add:

> -6- `iterator` of an associative container meets the requirements of the `BidirectionalIterator` concept. For associative containers where the value type is the same as the key type, both `iterator` and `const_iterator` are constant iterators. It is unspecified whether or not `iterator` and `const_iterator` are the same type. [Note: `iterator` and `const_iterator` have identical semantics in this case, and `iterator` is convertible to `const_iterator`. Users can avoid violating the One Definition Rule by always using `const_iterator` in their function parameter lists -- end note]

### 1044. Response to UK 325

Section: 30.4 [thread.mutex] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-18

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Discussion:

Addresses UK 325

We believe constexpr literal values should be a more natural expression of empty tag types than extern objects as it should improve the compiler's ability to optimize the empty object away completely.

[ Summit: ]

> Move to review. The current specification is a "hack", and the proposed specification is a better "hack".

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change the synopsis in 30.4 [thread.mutex]:

>     struct defer_lock_t {};
>     struct try_to_lock_t {};
>     struct adopt_lock_t {};

>     extern constexpr defer_lock_t defer_lock {};
>     extern constexpr try_to_lock_t try_to_lock {};
>     extern constexpr adopt_lock_t adopt_lock {};

### 1045. Response to UK 326

Section: 30.4.3.2.1 [thread.lock.unique.cons] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-12 Last modified: 2009-07-18

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Discussion:

Addresses UK 326

The precondition that the mutex is not owned by this thread offers introduces the risk of un-necessary undefined behaviour into the program. The only time it matters whether the current thread owns the mutex is in the lock operation, and that will happen subsequent to construction in this case. The lock operation has the identical pre-condition, so there is nothing gained by asserting that precondition earlier and denying the program the right to get into a valid state before calling lock.

[ Summit: ]

> Agree, move to review.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Strike 30.4.3.2.1 [thread.lock.unique.cons] p7:

>     unique_lock(mutex_type& m, defer_lock_t);

> > -7- Precondition: If `mutex_type` is not a recursive mutex the calling thread does not own the mutex.

### 1065. Response to UK 168

Section: 17.6.1.1 [contents] Status: WP Submitter: Howard Hinnant Opened: 2009-03-15 Last modified: 2009-07-18

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Discussion:

Addresses UK 168

We should make it clear (either by note or normatively) that namespace `std` may contain inline namespaces, and that entities specified to be defined in std may in fact be defined in one of these inline namespaces. (If we're going to use them for versioning, eg when TR2 comes along, we're going to need that.)

Replace "namespace std or namespaces nested within namespace std" with "namespace std or namespaces nested within namespace std or inline namespaces nested directly or indirectly within namespace std"

[ Summit: ]

> adopt UK words (some have reservations whether it is correct)

[ 2009-05-09 Alisdair improves the wording. ]

[ Batavia (2009-05): ]

> Bill believes there is strictly speaking no need to say that because no portable test can detect the difference. However he agrees that it doesn't hurt to say this.

> Move to Tentatively Ready.

Proposed resolution:

Change 17.6.1.1 [contents] p2:

> All library entities except macros, `operator new` and `operator delete` are defined within the namespace `std` or namespaces nested within namespace `std`. It is unspecified whether names declared in a specific namespace are declared directly in that namespace, or in an inline namespace inside that namespace. [Footnote: This gives implementers freedom to support multiple configurations of the library.]

### 1066. Response to UK 189 and JP 27

Section: 18 [language.support] Status: WP Submitter: Howard Hinnant Opened: 2009-03-15 Last modified: 2009-07-18

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Discussion:

Addresses UK 189 and JP 27

The addition of the `[[noreturn]]` attribute to the language will be an important aid for static analysis tools.

The following functions should be declared in C++ with the `[[noreturn]]` attribute: `abort` `exit` `quick_exit` `terminate` `unexpected` `rethrow_exception` `throw_with_nested`.

[ Summit: ]

> Agreed.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 18.5 [support.start.term] p3:

> -2- ...

>     void abort [[noreturn]] (void)

> -3- ...

> -6- ...

>     void exit [[noreturn]] (int status)

> -7- ...

> -11- ...

>     void quick_exit [[noreturn]] (int status)

> -12- ...

Change the `<exception>` synopsis in 18.8 [support.exception]:

>     void unexpected [[noreturn]] ();
>     ...
>     void terminate [[noreturn]] ();
>     ...
>     void rethrow_exception [[noreturn]] (exception_ptr p);
>     ...
>     template <class T> void throw_with_nested [[noreturn]] (T&& t); // [[noreturn]]

Change 18.8.2.4 [unexpected]:

>     void unexpected [[noreturn]] ();

Change 18.8.3.3 [terminate]:

>     void terminate [[noreturn]] ();

Change 18.8.5 [propagation]:

>     void rethrow_exception [[noreturn]] (exception_ptr p);

In the synopsis of 18.8.6 [except.nested] and the definition area change:

>     template <class T> void throw_with_nested [[noreturn]] (T&& t); // [[noreturn]]

### 1070. Ambiguous move overloads in function

Section: 20.7.15.2 [func.wrap.func] Status: WP Submitter: Howard Hinnant Opened: 2009-03-19 Last modified: 2009-07-18

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Discussion:

The synopsis in 20.7.15.2 [func.wrap.func] says:

>     template<Returnable R, CopyConstructible... ArgTypes>
>     class function<R(ArgTypes...)>
>     {
>         ...
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes...>
>                 && Convertible<Callable<F, ArgTypes...>::result_type, R>
>           function(F);
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes...>
>                 && Convertible<Callable<F, ArgTypes...>::result_type, R>
>           function(F&&);
>         ...
>         template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F);
>         template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F&&);
>         ...
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes..>
>                 && Convertible<Callable<F, ArgTypes...>::result_type
>           function& operator=(F);
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes...>
>                 && Convertible<Callable<F, ArgTypes...>::result_type, R>
>           function& operator=(F&&);
>         ...
>     };

Each of the 3 pairs above are ambiguous. We need only one of each pair, and we could do it with either one. If we choose the `F&&` version we need to bring `decay` into the definition to get the pass-by-value behavior. In the proposed wording I've gotten lazy and just used the pass-by-value signature.

[ 2009-05-01 Daniel adds: ]

> 1024 modifies the second removed constructor.

[ Batavia (2009-05): ]

> We briefly discussed whether we ought support moveable function objects, but decided that should be a separate issue if someone cares to propose it.

> Move to Tentatively Ready.

Proposed resolution:

Change the synopsis of 20.7.15.2 [func.wrap.func], and remove the associated definitions in 20.7.15.2.1 [func.wrap.func.con]:

>     template<Returnable R, CopyConstructible... ArgTypes>
>     class function<R(ArgTypes...)>
>     {
>         ...
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes...>
>                 && Convertible<Callable<F, ArgTypes...>::result_type, R>
>           function(F);
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes...>
>                 && Convertible<Callable<F, ArgTypes...>::result_type, R>
>           function(F&&);
>         ...
>         template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F);
>         template<class F, Allocator Alloc> function(allocator_arg_t, const Alloc&, F&&);
>         ...
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes..>
>                 && Convertible<Callable<F, ArgTypes...>::result_type
>           function& operator=(F);
>         template<class F>
>           requires CopyConstructible<F> && Callable<F, ArgTypes...>
>                 && Convertible<Callable<F, ArgTypes...>::result_type, R>
>           function& operator=(F&&);
>         ...
>     };

### 1073. Declaration of `allocator_arg` should be `constexpr`

Section: 20.8 [memory] Status: WP Submitter: Alisdair Meredith Opened: 2009-03-19 Last modified: 2009-07-18

View all other issues in [memory].

View all issues with WP status.

Discussion:

Declaration of `allocator_arg` should be `constexpr` to ensure constant initialization.

[ Batavia (2009-05): ]

> We agree with the proposed resolution. Move to Tentatively Ready.

Proposed resolution:

Change 20.8 [memory] p2:

>     // 20.8.1, allocator argument tag
>     struct allocator_arg_t { };
>     constexpr allocator_arg_t allocator_arg = allocator_arg_t();

### 1103. `system_error` constructor postcondition overly strict

Section: 19.5.5.2 [syserr.syserr.members] Status: WP Submitter: Howard Hinnant Opened: 2009-04-25 Last modified: 2009-07-18

View all issues with WP status.

Discussion:

19.5.5.2 [syserr.syserr.members] says:

>     system_error(error_code ec, const string& what_arg);

> > Effects: Constructs an object of class `system_error`.

> > Postconditions: `code() == ec` and `strcmp(runtime_error::what(), what_arg.c_str()) == 0`.

However the intent is for:

>     std::system_error se(std::errc::not_a_directory, "In FooBar");
>     ...
>     se.what();  // returns something along the lines of:
>                 //   "In FooBar: Not a directory"

The way the constructor postconditions are set up now, to achieve both conformance, and the desired intent in the `what()` string, the `system_error` constructor must store "In FooBar" in the base class, and then form the desired output each time `what()` is called. Or alternatively, store "In FooBar" in the base class, and store the desired `what()` string in the derived `system_error`, and override `what()` to return the string in the derived part.

Both of the above implementations seem suboptimal to me. In one I'm computing a new string every time `what()` is called. And since `what()` can't propagate exceptions, the client may get a different string on different calls.

The second solution requires storing two strings instead of one.

What I would like to be able to do is form the desired `what()` string once in the `system_error` constructor, and store that in the base class. Now I'm:

1. Computing the desired `what()` only once.
2. The base class `what()` definition is sufficient and nothrow.
3. I'm not storing multiple strings.

This is smaller code, smaller data, and faster.

`ios_base::failure` has the same issue.

[ Comments about this change received favorable comments from the `system_error` designers. ]

[ Batavia (2009-05): ]

> We agree with the proposed resolution.

> Move to Tentatively Ready.

Proposed resolution:

In 19.5.5.2 [syserr.syserr.members], change the following constructor postconditions:

>     system_error(error_code ec, const string& what_arg);

> > -2- Postconditions: `code() == ec` and `strcmp(runtime_error::what(), what_arg.c_str()) == 0 string(what()).find(what_arg) != string::npos`.

>     system_error(error_code ec, const char* what_arg);

> > -4- Postconditions: `code() == ec` and `strcmp(runtime_error::what(), what_arg) == 0 string(what()).find(what_arg) != string::npos`.

>     system_error(error_code ec);

> > -6- Postconditions: `code() == ec` and `strcmp(runtime_error::what(), ""`.

>     system_error(int ev, const error_category& ecat, const string& what_arg);

> > -8- Postconditions: `code() == error_code(ev, ecat)` and `strcmp(runtime_error::what(), what_arg.c_str()) == 0 string(what()).find(what_arg) != string::npos`.

>     system_error(int ev, const error_category& ecat, const char* what_arg);

> > -10- Postconditions: `code() == error_code(ev, ecat)` and `strcmp(runtime_error::what(), what_arg) == 0 string(what()).find(what_arg) != string::npos`.

>     system_error(int ev, const error_category& ecat);

> > -12- Postconditions: `code() == error_code(ev, ecat)` and `strcmp(runtime_error::what(), "") == 0`.

In 19.5.5.2 [syserr.syserr.members], change the description of `what()`:

>     const char *what() const throw();

> > -14- Returns: An NTBS incorporating `runtime_error::what()` and `code().message()` the arguments supplied in the constructor.

> > [Note: One possible implementation would be: The return NTBS might take the form: `what_arg + ": " + code().message()`

> > >     if (msg.empty()) {
> > >       try {
> > >         string tmp = runtime_error::what();
> > >         if (code()) {
> > >           if (!tmp.empty())
> > >             tmp += ": ";
> > >           tmp += code().message();
> > >         }
> > >         swap(msg, tmp);
> > >       } catch(...) {
> > >         return runtime_error::what();
> > >       }
> > >     return msg.c_str();

> > — end note]

In 27.5.2.1.1 [ios::failure], change the synopsis:

>     namespace std {
>       class ios_base::failure : public system_error {
>       public:
>         explicit failure(const string& msg, const error_code& ec = io_errc::stream);
>         explicit failure(const char* msg, const error_code& ec = io_errc::stream);
>         virtual const char* what() const throw();
>       };
>     }

In 27.5.2.1.1 [ios::failure], change the description of the constructors:

>     explicit failure(const string& msg, , const error_code& ec = io_errc::stream);

> > -3- Effects: Constructs an object of class `failure` by constructing the base class with `msg` and `ec`.

> > -4- Postcondition: `code() == ec` and `strcmp(what(), msg.c_str()) == 0`

>     explicit failure(const char* msg, const error_code& ec = io_errc::stream);

> > -5- Effects: Constructs an object of class `failure` by constructing the base class with `msg` and `ec`.

> > -6- Postcondition: `code() == ec and strcmp(what(), msg) == 0`

In 27.5.2.1.1 [ios::failure], remove `what` (the base class definition need not be repeated here).

>     const char* what() const;

> > -7- Returns: The message `msg` with which the exception was created.

### 1178. Header dependencies

Section: 17.6.4.2 [res.on.headers] Status: WP Submitter: Beman Dawes Opened: 2009-07-18 Last modified: 2009-10-26

View all issues with WP status.

Discussion:

See Frankfurt notes of 1001.

Proposed resolution:

Change 17.6.4.2 [res.on.headers], Headers, paragraph 1, as indicated:

> A C++ header may include other C++ headers.[footnote] A C++ header shall provide the declarations and definitions that appear in its synopsis (3.2 [basic.def.odr]). A C++ header shown in its synopsis as including other C++ headers shall provide the declarations and definitions that appear in the synopses of those other headers.

> [footnote] C++ headers must include a C++ header that contains any needed definition (3.2).