# rc_string_base.h

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    00001 // Reference-counted versatile string base -*- C++ -*-
    00002
    00003 // Copyright (C) 2005, 2006 Free Software Foundation, Inc.
    00004 //
    00005 // This file is part of the GNU ISO C++ Library.  This library is free
    00006 // software; you can redistribute it and/or modify it under the
    00007 // terms of the GNU General Public License as published by the
    00008 // Free Software Foundation; either version 2, or (at your option)
    00009 // any later version.
    00010
    00011 // This library is distributed in the hope that it will be useful,
    00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
    00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    00014 // GNU General Public License for more details.
    00015
    00016 // You should have received a copy of the GNU General Public License along
    00017 // with this library; see the file COPYING.  If not, write to the Free
    00018 // Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
    00019 // USA.
    00020
    00021 // As a special exception, you may use this file as part of a free software
    00022 // library without restriction.  Specifically, if other files instantiate
    00023 // templates or use macros or inline functions from this file, or you compile
    00024 // this file and link it with other files to produce an executable, this
    00025 // file does not by itself cause the resulting executable to be covered by
    00026 // the GNU General Public License.  This exception does not however
    00027 // invalidate any other reasons why the executable file might be covered by
    00028 // the GNU General Public License.
    00029
    00030 /** @file ext/rc_string_base.h
    00031  *  This file is a GNU extension to the Standard C++ Library.
    00032  *  This is an internal header file, included by other library headers.
    00033  *  You should not attempt to use it directly.
    00034  */
    00035
    00036 #ifndef _RC_STRING_BASE_H
    00037 #define _RC_STRING_BASE_H 1
    00038
    00039 #include <ext/atomicity.h>
    00040
    00041 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
    00042
    00043   /**
    00044    *  @if maint
    00045    *  Documentation?  What's that?
    00046    *  Nathan Myers <ncm@cantrip.org>.
    00047    *
    00048    *  A string looks like this:
    00049    *
    00050    *  @code
    00051    *                                        [_Rep]
    00052    *                                        _M_length
    00053    *   [__rc_string_base<char_type>]        _M_capacity
    00054    *   _M_dataplus                          _M_refcount
    00055    *   _M_p ---------------->               unnamed array of char_type
    00056    *  @endcode
    00057    *
    00058    *  Where the _M_p points to the first character in the string, and
    00059    *  you cast it to a pointer-to-_Rep and subtract 1 to get a
    00060    *  pointer to the header.
    00061    *
    00062    *  This approach has the enormous advantage that a string object
    00063    *  requires only one allocation.  All the ugliness is confined
    00064    *  within a single pair of inline functions, which each compile to
    00065    *  a single "add" instruction: _Rep::_M_refdata(), and
    00066    *  __rc_string_base::_M_rep(); and the allocation function which gets a
    00067    *  block of raw bytes and with room enough and constructs a _Rep
    00068    *  object at the front.
    00069    *
    00070    *  The reason you want _M_data pointing to the character array and
    00071    *  not the _Rep is so that the debugger can see the string
    00072    *  contents. (Probably we should add a non-inline member to get
    00073    *  the _Rep for the debugger to use, so users can check the actual
    00074    *  string length.)
    00075    *
    00076    *  Note that the _Rep object is a POD so that you can have a
    00077    *  static "empty string" _Rep object already "constructed" before
    00078    *  static constructors have run.  The reference-count encoding is
    00079    *  chosen so that a 0 indicates one reference, so you never try to
    00080    *  destroy the empty-string _Rep object.
    00081    *
    00082    *  All but the last paragraph is considered pretty conventional
    00083    *  for a C++ string implementation.
    00084    *  @endif
    00085   */
    00086  template<typename _CharT, typename _Traits, typename _Alloc>
    00087     class __rc_string_base
    00088     : protected __vstring_utility<_CharT, _Traits, _Alloc>
    00089     {
    00090     public:
    00091       typedef _Traits                       traits_type;
    00092       typedef typename _Traits::char_type           value_type;
    00093       typedef _Alloc                        allocator_type;
    00094
    00095       typedef __vstring_utility<_CharT, _Traits, _Alloc>    _Util_Base;
    00096       typedef typename _Util_Base::_CharT_alloc_type        _CharT_alloc_type;
    00097       typedef typename _CharT_alloc_type::size_type     size_type;
    00098
    00099     private:
    00100       // _Rep: string representation
    00101       //   Invariants:
    00102       //   1. String really contains _M_length + 1 characters: due to 21.3.4
    00103       //      must be kept null-terminated.
    00104       //   2. _M_capacity >= _M_length
    00105       //      Allocated memory is always (_M_capacity + 1) * sizeof(_CharT).
    00106       //   3. _M_refcount has three states:
    00107       //      -1: leaked, one reference, no ref-copies allowed, non-const.
    00108       //       0: one reference, non-const.
    00109       //     n>0: n + 1 references, operations require a lock, const.
    00110       //   4. All fields == 0 is an empty string, given the extra storage
    00111       //      beyond-the-end for a null terminator; thus, the shared
    00112       //      empty string representation needs no constructor.
    00113       struct _Rep
    00114       {
    00115     union
    00116     {
    00117       struct
    00118       {
    00119         size_type       _M_length;
    00120         size_type       _M_capacity;
    00121         _Atomic_word    _M_refcount;
    00122       }                 _M_info;
    00123
    00124       // Only for alignment purposes.
    00125       _CharT            _M_align;
    00126     };
    00127
    00128     typedef typename _Alloc::template rebind<_Rep>::other _Rep_alloc_type;
    00129
    00130     _CharT*
    00131     _M_refdata() throw()
    00132     { return reinterpret_cast<_CharT*>(this + 1); }
    00133
    00134     _CharT*
    00135     _M_refcopy() throw()
    00136     {
    00137       __atomic_add_dispatch(&_M_info._M_refcount, 1);
    00138       return _M_refdata();
    00139     }  // XXX MT
    00140
    00141     void
    00142     _M_set_length(size_type __n)
    00143     {
    00144       _M_info._M_refcount = 0;  // One reference.
    00145       _M_info._M_length = __n;
    00146       // grrr. (per 21.3.4)
    00147       // You cannot leave those LWG people alone for a second.
    00148       traits_type::assign(_M_refdata()[__n], _CharT());
    00149     }
    00150
    00151     // Create & Destroy
    00152     static _Rep*
    00153     _S_create(size_type, size_type, const _Alloc&);
    00154
    00155     void
    00156     _M_destroy(const _Alloc&) throw();
    00157
    00158     _CharT*
    00159     _M_clone(const _Alloc&, size_type __res = 0);
    00160       };
    00161
    00162       struct _Rep_empty
    00163       : public _Rep
    00164       {
    00165     _CharT              _M_terminal;
    00166       };
    00167
    00168       static _Rep_empty     _S_empty_rep;
    00169
    00170       // The maximum number of individual char_type elements of an
    00171       // individual string is determined by _S_max_size. This is the
    00172       // value that will be returned by max_size().  (Whereas npos
    00173       // is the maximum number of bytes the allocator can allocate.)
    00174       // If one was to divvy up the theoretical largest size string,
    00175       // with a terminating character and m _CharT elements, it'd
    00176       // look like this:
    00177       // npos = sizeof(_Rep) + (m * sizeof(_CharT)) + sizeof(_CharT)
    00178       //        + sizeof(_Rep) - 1
    00179       // (NB: last two terms for rounding reasons, see _M_create below)
    00180       // Solving for m:
    00181       // m = ((npos - 2 * sizeof(_Rep) + 1) / sizeof(_CharT)) - 1
    00182       // In addition, this implementation halfs this amount.
    00183       enum { _S_max_size = (((static_cast<size_type>(-1) - 2 * sizeof(_Rep)
    00184                   + 1) / sizeof(_CharT)) - 1) / 2 };
    00185
    00186       // Data Member (private):
    00187       mutable typename _Util_Base::template _Alloc_hider<_Alloc>  _M_dataplus;
    00188
    00189       void
    00190       _M_data(_CharT* __p)
    00191       { _M_dataplus._M_p = __p; }
    00192
    00193       _Rep*
    00194       _M_rep() const
    00195       { return &((reinterpret_cast<_Rep*>(_M_data()))[-1]); }
    00196
    00197       _CharT*
    00198       _M_grab(const _Alloc& __alloc) const
    00199       {
    00200     return (!_M_is_leaked() && _M_get_allocator() == __alloc)
    00201             ? _M_rep()->_M_refcopy() : _M_rep()->_M_clone(__alloc);
    00202       }
    00203
    00204       void
    00205       _M_dispose()
    00206       {
    00207     if (__exchange_and_add_dispatch(&_M_rep()->_M_info._M_refcount,
    00208                     -1) <= 0)
    00209       _M_rep()->_M_destroy(_M_get_allocator());
    00210       }  // XXX MT
    00211
    00212       bool
    00213       _M_is_leaked() const
    00214       { return _M_rep()->_M_info._M_refcount < 0; }
    00215
    00216       void
    00217       _M_set_sharable()
    00218       { _M_rep()->_M_info._M_refcount = 0; }
    00219
    00220       void
    00221       _M_leak_hard();
    00222
    00223       // _S_construct_aux is used to implement the 21.3.1 para 15 which
    00224       // requires special behaviour if _InIterator is an integral type
    00225       template<typename _InIterator>
    00226         static _CharT*
    00227         _S_construct_aux(_InIterator __beg, _InIterator __end,
    00228              const _Alloc& __a, std::__false_type)
    00229     {
    00230           typedef typename iterator_traits<_InIterator>::iterator_category _Tag;
    00231           return _S_construct(__beg, __end, __a, _Tag());
    00232     }
    00233
    00234       template<typename _InIterator>
    00235         static _CharT*
    00236         _S_construct_aux(_InIterator __beg, _InIterator __end,
    00237              const _Alloc& __a, std::__true_type)
    00238     { return _S_construct(static_cast<size_type>(__beg),
    00239                   static_cast<value_type>(__end), __a); }
    00240
    00241       template<typename _InIterator>
    00242         static _CharT*
    00243         _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a)
    00244     {
    00245       typedef typename std::__is_integer<_InIterator>::__type _Integral;
    00246       return _S_construct_aux(__beg, __end, __a, _Integral());
    00247         }
    00248
    00249       // For Input Iterators, used in istreambuf_iterators, etc.
    00250       template<typename _InIterator>
    00251         static _CharT*
    00252          _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
    00253               std::input_iterator_tag);
    00254
    00255       // For forward_iterators up to random_access_iterators, used for
    00256       // string::iterator, _CharT*, etc.
    00257       template<typename _FwdIterator>
    00258         static _CharT*
    00259         _S_construct(_FwdIterator __beg, _FwdIterator __end, const _Alloc& __a,
    00260              std::forward_iterator_tag);
    00261
    00262       static _CharT*
    00263       _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
    00264
    00265     public:
    00266       size_type
    00267       _M_max_size() const
    00268       { return size_type(_S_max_size); }
    00269
    00270       _CharT*
    00271       _M_data() const
    00272       { return _M_dataplus._M_p; }
    00273
    00274       size_type
    00275       _M_length() const
    00276       { return _M_rep()->_M_info._M_length; }
    00277
    00278       size_type
    00279       _M_capacity() const
    00280       { return _M_rep()->_M_info._M_capacity; }
    00281
    00282       bool
    00283       _M_is_shared() const
    00284       { return _M_rep()->_M_info._M_refcount > 0; }
    00285
    00286       void
    00287       _M_set_leaked()
    00288       { _M_rep()->_M_info._M_refcount = -1; }
    00289
    00290       void
    00291       _M_leak()    // for use in begin() & non-const op[]
    00292       {
    00293     if (!_M_is_leaked())
    00294       _M_leak_hard();
    00295       }
    00296
    00297       void
    00298       _M_set_length(size_type __n)
    00299       { _M_rep()->_M_set_length(__n); }
    00300
    00301       __rc_string_base()
    00302       : _M_dataplus(_Alloc(), _S_empty_rep._M_refcopy()) { }
    00303
    00304       __rc_string_base(const _Alloc& __a);
    00305
    00306       __rc_string_base(const __rc_string_base& __rcs);
    00307
    00308       __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a);
    00309
    00310       template<typename _InputIterator>
    00311         __rc_string_base(_InputIterator __beg, _InputIterator __end,
    00312              const _Alloc& __a);
    00313
    00314       ~__rc_string_base()
    00315       { _M_dispose(); }
    00316
    00317       allocator_type&
    00318       _M_get_allocator()
    00319       { return _M_dataplus; }
    00320
    00321       const allocator_type&
    00322       _M_get_allocator() const
    00323       { return _M_dataplus; }
    00324
    00325       void
    00326       _M_swap(__rc_string_base& __rcs);
    00327
    00328       void
    00329       _M_assign(const __rc_string_base& __rcs);
    00330
    00331       void
    00332       _M_reserve(size_type __res);
    00333
    00334       void
    00335       _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
    00336         size_type __len2);
    00337
    00338       void
    00339       _M_erase(size_type __pos, size_type __n);
    00340
    00341       void
    00342       _M_clear()
    00343       { _M_erase(size_type(0), _M_length()); }
    00344
    00345       bool
    00346       _M_compare(const __rc_string_base&) const
    00347       { return false; }
    00348     };
    00349
    00350   template<typename _CharT, typename _Traits, typename _Alloc>
    00351     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep_empty
    00352     __rc_string_base<_CharT, _Traits, _Alloc>::_S_empty_rep;
    00353
    00354   template<typename _CharT, typename _Traits, typename _Alloc>
    00355     typename __rc_string_base<_CharT, _Traits, _Alloc>::_Rep*
    00356     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    00357     _S_create(size_type __capacity, size_type __old_capacity,
    00358           const _Alloc& __alloc)
    00359     {
    00360       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00361       // 83.  String::npos vs. string::max_size()
    00362       if (__capacity > size_type(_S_max_size))
    00363     std::__throw_length_error(__N("__rc_string_base::_Rep::_S_create"));
    00364
    00365       // The standard places no restriction on allocating more memory
    00366       // than is strictly needed within this layer at the moment or as
    00367       // requested by an explicit application call to reserve().
    00368
    00369       // Many malloc implementations perform quite poorly when an
    00370       // application attempts to allocate memory in a stepwise fashion
    00371       // growing each allocation size by only 1 char.  Additionally,
    00372       // it makes little sense to allocate less linear memory than the
    00373       // natural blocking size of the malloc implementation.
    00374       // Unfortunately, we would need a somewhat low-level calculation
    00375       // with tuned parameters to get this perfect for any particular
    00376       // malloc implementation.  Fortunately, generalizations about
    00377       // common features seen among implementations seems to suffice.
    00378
    00379       // __pagesize need not match the actual VM page size for good
    00380       // results in practice, thus we pick a common value on the low
    00381       // side.  __malloc_header_size is an estimate of the amount of
    00382       // overhead per memory allocation (in practice seen N * sizeof
    00383       // (void*) where N is 0, 2 or 4).  According to folklore,
    00384       // picking this value on the high side is better than
    00385       // low-balling it (especially when this algorithm is used with
    00386       // malloc implementations that allocate memory blocks rounded up
    00387       // to a size which is a power of 2).
    00388       const size_type __pagesize = 4096;
    00389       const size_type __malloc_header_size = 4 * sizeof(void*);
    00390
    00391       // The below implements an exponential growth policy, necessary to
    00392       // meet amortized linear time requirements of the library: see
    00393       // http://gcc.gnu.org/ml/libstdc++/2001-07/msg00085.html.
    00394       if (__capacity > __old_capacity && __capacity < 2 * __old_capacity)
    00395     {
    00396       __capacity = 2 * __old_capacity;
    00397       // Never allocate a string bigger than _S_max_size.
    00398       if (__capacity > size_type(_S_max_size))
    00399         __capacity = size_type(_S_max_size);
    00400     }
    00401
    00402       // NB: Need an array of char_type[__capacity], plus a terminating
    00403       // null char_type() element, plus enough for the _Rep data structure,
    00404       // plus sizeof(_Rep) - 1 to upper round to a size multiple of
    00405       // sizeof(_Rep).
    00406       // Whew. Seemingly so needy, yet so elemental.
    00407       size_type __size = ((__capacity + 1) * sizeof(_CharT)
    00408               + 2 * sizeof(_Rep) - 1);
    00409
    00410       const size_type __adj_size = __size + __malloc_header_size;
    00411       if (__adj_size > __pagesize && __capacity > __old_capacity)
    00412     {
    00413       const size_type __extra = __pagesize - __adj_size % __pagesize;
    00414       __capacity += __extra / sizeof(_CharT);
    00415       if (__capacity > size_type(_S_max_size))
    00416         __capacity = size_type(_S_max_size);
    00417       __size = (__capacity + 1) * sizeof(_CharT) + 2 * sizeof(_Rep) - 1;
    00418     }
    00419
    00420       // NB: Might throw, but no worries about a leak, mate: _Rep()
    00421       // does not throw.
    00422       _Rep* __place = _Rep_alloc_type(__alloc).allocate(__size / sizeof(_Rep));
    00423       _Rep* __p = new (__place) _Rep;
    00424       __p->_M_info._M_capacity = __capacity;
    00425       return __p;
    00426     }
    00427
    00428   template<typename _CharT, typename _Traits, typename _Alloc>
    00429     void
    00430     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    00431     _M_destroy(const _Alloc& __a) throw ()
    00432     {
    00433       const size_type __size = ((_M_info._M_capacity + 1) * sizeof(_CharT)
    00434                 + 2 * sizeof(_Rep) - 1);
    00435       _Rep_alloc_type(__a).deallocate(this, __size / sizeof(_Rep));
    00436     }
    00437
    00438   template<typename _CharT, typename _Traits, typename _Alloc>
    00439     _CharT*
    00440     __rc_string_base<_CharT, _Traits, _Alloc>::_Rep::
    00441     _M_clone(const _Alloc& __alloc, size_type __res)
    00442     {
    00443       // Requested capacity of the clone.
    00444       const size_type __requested_cap = _M_info._M_length + __res;
    00445       _Rep* __r = _Rep::_S_create(__requested_cap, _M_info._M_capacity,
    00446                   __alloc);
    00447
    00448       if (_M_info._M_length)
    00449     _S_copy(__r->_M_refdata(), _M_refdata(), _M_info._M_length);
    00450
    00451       __r->_M_set_length(_M_info._M_length);
    00452       return __r->_M_refdata();
    00453     }
    00454
    00455   template<typename _CharT, typename _Traits, typename _Alloc>
    00456     __rc_string_base<_CharT, _Traits, _Alloc>::
    00457     __rc_string_base(const _Alloc& __a)
    00458     : _M_dataplus(__a, _S_construct(size_type(), _CharT(), __a)) { }
    00459
    00460   template<typename _CharT, typename _Traits, typename _Alloc>
    00461     __rc_string_base<_CharT, _Traits, _Alloc>::
    00462     __rc_string_base(const __rc_string_base& __rcs)
    00463     : _M_dataplus(__rcs._M_get_allocator(),
    00464           __rcs._M_grab(__rcs._M_get_allocator())) { }
    00465
    00466   template<typename _CharT, typename _Traits, typename _Alloc>
    00467     __rc_string_base<_CharT, _Traits, _Alloc>::
    00468     __rc_string_base(size_type __n, _CharT __c, const _Alloc& __a)
    00469     : _M_dataplus(__a, _S_construct(__n, __c, __a)) { }
    00470
    00471   template<typename _CharT, typename _Traits, typename _Alloc>
    00472     template<typename _InputIterator>
    00473     __rc_string_base<_CharT, _Traits, _Alloc>::
    00474     __rc_string_base(_InputIterator __beg, _InputIterator __end,
    00475              const _Alloc& __a)
    00476     : _M_dataplus(__a, _S_construct(__beg, __end, __a)) { }
    00477
    00478   template<typename _CharT, typename _Traits, typename _Alloc>
    00479     void
    00480     __rc_string_base<_CharT, _Traits, _Alloc>::
    00481     _M_leak_hard()
    00482     {
    00483       if (_M_is_shared())
    00484     _M_erase(0, 0);
    00485       _M_set_leaked();
    00486     }
    00487
    00488   // NB: This is the special case for Input Iterators, used in
    00489   // istreambuf_iterators, etc.
    00490   // Input Iterators have a cost structure very different from
    00491   // pointers, calling for a different coding style.
    00492   template<typename _CharT, typename _Traits, typename _Alloc>
    00493     template<typename _InIterator>
    00494       _CharT*
    00495       __rc_string_base<_CharT, _Traits, _Alloc>::
    00496       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
    00497            std::input_iterator_tag)
    00498       {
    00499     if (__beg == __end && __a == _Alloc())
    00500       return _S_empty_rep._M_refcopy();
    00501
    00502     // Avoid reallocation for common case.
    00503     _CharT __buf[128];
    00504     size_type __len = 0;
    00505     while (__beg != __end && __len < sizeof(__buf) / sizeof(_CharT))
    00506       {
    00507         __buf[__len++] = *__beg;
    00508         ++__beg;
    00509       }
    00510     _Rep* __r = _Rep::_S_create(__len, size_type(0), __a);
    00511     _S_copy(__r->_M_refdata(), __buf, __len);
    00512     try
    00513       {
    00514         while (__beg != __end)
    00515           {
    00516         if (__len == __r->_M_info._M_capacity)
    00517           {
    00518             // Allocate more space.
    00519             _Rep* __another = _Rep::_S_create(__len + 1, __len, __a);
    00520             _S_copy(__another->_M_refdata(), __r->_M_refdata(), __len);
    00521             __r->_M_destroy(__a);
    00522             __r = __another;
    00523           }
    00524         __r->_M_refdata()[__len++] = *__beg;
    00525         ++__beg;
    00526           }
    00527       }
    00528     catch(...)
    00529       {
    00530         __r->_M_destroy(__a);
    00531         __throw_exception_again;
    00532       }
    00533     __r->_M_set_length(__len);
    00534     return __r->_M_refdata();
    00535       }
    00536
    00537   template<typename _CharT, typename _Traits, typename _Alloc>
    00538     template<typename _InIterator>
    00539       _CharT*
    00540       __rc_string_base<_CharT, _Traits, _Alloc>::
    00541       _S_construct(_InIterator __beg, _InIterator __end, const _Alloc& __a,
    00542            std::forward_iterator_tag)
    00543       {
    00544     if (__beg == __end && __a == _Alloc())
    00545       return _S_empty_rep._M_refcopy();
    00546
    00547     // NB: Not required, but considered best practice.
    00548     if (__builtin_expect(_S_is_null_pointer(__beg) && __beg != __end, 0))
    00549       std::__throw_logic_error(__N("__rc_string_base::"
    00550                        "_S_construct NULL not valid"));
    00551
    00552     const size_type __dnew = static_cast<size_type>(std::distance(__beg,
    00553                                       __end));
    00554     // Check for out_of_range and length_error exceptions.
    00555     _Rep* __r = _Rep::_S_create(__dnew, size_type(0), __a);
    00556     try
    00557       { _S_copy_chars(__r->_M_refdata(), __beg, __end); }
    00558     catch(...)
    00559       {
    00560         __r->_M_destroy(__a);
    00561         __throw_exception_again;
    00562       }
    00563     __r->_M_set_length(__dnew);
    00564     return __r->_M_refdata();
    00565       }
    00566
    00567   template<typename _CharT, typename _Traits, typename _Alloc>
    00568     _CharT*
    00569     __rc_string_base<_CharT, _Traits, _Alloc>::
    00570     _S_construct(size_type __n, _CharT __c, const _Alloc& __a)
    00571     {
    00572       if (__n == 0 && __a == _Alloc())
    00573     return _S_empty_rep._M_refcopy();
    00574
    00575       // Check for out_of_range and length_error exceptions.
    00576       _Rep* __r = _Rep::_S_create(__n, size_type(0), __a);
    00577       if (__n)
    00578     _S_assign(__r->_M_refdata(), __n, __c);
    00579
    00580       __r->_M_set_length(__n);
    00581       return __r->_M_refdata();
    00582     }
    00583
    00584   template<typename _CharT, typename _Traits, typename _Alloc>
    00585     void
    00586     __rc_string_base<_CharT, _Traits, _Alloc>::
    00587     _M_swap(__rc_string_base& __rcs)
    00588     {
    00589       if (_M_is_leaked())
    00590     _M_set_sharable();
    00591       if (__rcs._M_is_leaked())
    00592     __rcs._M_set_sharable();
    00593
    00594       _CharT* __tmp = _M_data();
    00595       _M_data(__rcs._M_data());
    00596       __rcs._M_data(__tmp);
    00597
    00598       // _GLIBCXX_RESOLVE_LIB_DEFECTS
    00599       // 431. Swapping containers with unequal allocators.
    00600       std::__alloc_swap<allocator_type>::_S_do_it(_M_get_allocator(),
    00601                           __rcs._M_get_allocator());
    00602     }
    00603
    00604   template<typename _CharT, typename _Traits, typename _Alloc>
    00605     void
    00606     __rc_string_base<_CharT, _Traits, _Alloc>::
    00607     _M_assign(const __rc_string_base& __rcs)
    00608     {
    00609       if (_M_rep() != __rcs._M_rep())
    00610     {
    00611       _CharT* __tmp = __rcs._M_grab(_M_get_allocator());
    00612       _M_dispose();
    00613       _M_data(__tmp);
    00614     }
    00615     }
    00616
    00617   template<typename _CharT, typename _Traits, typename _Alloc>
    00618     void
    00619     __rc_string_base<_CharT, _Traits, _Alloc>::
    00620     _M_reserve(size_type __res)
    00621     {
    00622       // Make sure we don't shrink below the current size.
    00623       if (__res < _M_length())
    00624     __res = _M_length();
    00625
    00626       if (__res != _M_capacity() || _M_is_shared())
    00627     {
    00628       _CharT* __tmp = _M_rep()->_M_clone(_M_get_allocator(),
    00629                          __res - _M_length());
    00630       _M_dispose();
    00631       _M_data(__tmp);
    00632     }
    00633     }
    00634
    00635   template<typename _CharT, typename _Traits, typename _Alloc>
    00636     void
    00637     __rc_string_base<_CharT, _Traits, _Alloc>::
    00638     _M_mutate(size_type __pos, size_type __len1, const _CharT* __s,
    00639           size_type __len2)
    00640     {
    00641       const size_type __how_much = _M_length() - __pos - __len1;
    00642
    00643       _Rep* __r = _Rep::_S_create(_M_length() + __len2 - __len1,
    00644                   _M_capacity(), _M_get_allocator());
    00645
    00646       if (__pos)
    00647     _S_copy(__r->_M_refdata(), _M_data(), __pos);
    00648       if (__s && __len2)
    00649     _S_copy(__r->_M_refdata() + __pos, __s, __len2);
    00650       if (__how_much)
    00651     _S_copy(__r->_M_refdata() + __pos + __len2,
    00652         _M_data() + __pos + __len1, __how_much);
    00653
    00654       _M_dispose();
    00655       _M_data(__r->_M_refdata());
    00656     }
    00657
    00658   template<typename _CharT, typename _Traits, typename _Alloc>
    00659     void
    00660     __rc_string_base<_CharT, _Traits, _Alloc>::
    00661     _M_erase(size_type __pos, size_type __n)
    00662     {
    00663       const size_type __new_size = _M_length() - __n;
    00664       const size_type __how_much = _M_length() - __pos - __n;
    00665
    00666       if (_M_is_shared())
    00667     {
    00668       // Must reallocate.
    00669       _Rep* __r = _Rep::_S_create(__new_size, _M_capacity(),
    00670                       _M_get_allocator());
    00671
    00672       if (__pos)
    00673         _S_copy(__r->_M_refdata(), _M_data(), __pos);
    00674       if (__how_much)
    00675         _S_copy(__r->_M_refdata() + __pos,
    00676             _M_data() + __pos + __n, __how_much);
    00677
    00678       _M_dispose();
    00679       _M_data(__r->_M_refdata());
    00680     }
    00681       else if (__how_much && __n)
    00682     {
    00683       // Work in-place.
    00684       _S_move(_M_data() + __pos,
    00685           _M_data() + __pos + __n, __how_much);
    00686     }
    00687
    00688       _M_rep()->_M_set_length(__new_size);
    00689     }
    00690
    00691   template<>
    00692     inline bool
    00693     __rc_string_base<char, std::char_traits<char>,
    00694              std::allocator<char> >::
    00695     _M_compare(const __rc_string_base& __rcs) const
    00696     {
    00697       if (_M_rep() == __rcs._M_rep())
    00698     return true;
    00699       return false;
    00700     }
    00701
    00702 #ifdef _GLIBCXX_USE_WCHAR_T
    00703   template<>
    00704     inline bool
    00705     __rc_string_base<wchar_t, std::char_traits<wchar_t>,
    00706              std::allocator<wchar_t> >::
    00707     _M_compare(const __rc_string_base& __rcs) const
    00708     {
    00709       if (_M_rep() == __rcs._M_rep())
    00710     return true;
    00711       return false;
    00712     }
    00713 #endif
    00714
    00715 _GLIBCXX_END_NAMESPACE
    00716
    00717 #endif /* _RC_STRING_BASE_H */