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Developing Qore Modules

# Qore Module development

## Module Header Info

To develop a Qore module, several functions and several global variables must be declared in the module with public visibility so the module can be initialized and used by the Qore library.

The global variables are as follows:

- char `qore_module_name`[] - must give the name of the feature provided by the module.
- char `qore_module_version`[] - must give the version of the module
- char `qore_module_description`[] - a description of the module
- char `qore_module_author`[] - the author of the module
- char `qore_module_url`[] - a URL for the module
- int `qore_module_api_major` - must be assigned to QORE_MODULE_API_MAJOR
- int `qore_module_api_minor` - must be assigned to QORE_MODULE_API_MINOR
- qore_license_t `qore_module_license` - must be assigned to either QL_GPL or QL_LGPL according to the license the module requires; if the module links with GPL code, then QL_GPL must be used; otherwise if it is compatible with the LGPL then QL_LGPL must be used

The functions are as follows:

- qore_module_init_t `qore_module_init` - the module initialization function
- qore_module_ns_init_t `qore_module_ns_init` - the module namespace delta functions
- qore_module_delete_t `qore_module_delete` - the module deletion function

Note
  All variables and all functions are required, even if the functions are empty.

Here is an example:

DLLEXPORT char qore_module_name[] = "ncurses";
DLLEXPORT char qore_module_version[] = "0.1";
DLLEXPORT char qore_module_description[] = "ncurses class module";
DLLEXPORT char qore_module_author[] = "David Nichols";
DLLEXPORT char qore_module_url[] = "http://qore.sourceforge.net";
DLLEXPORT int qore_module_api_major = QORE_MODULE_API_MAJOR;
DLLEXPORT int qore_module_api_minor = QORE_MODULE_API_MINOR;
DLLEXPORT qore_license_t qore_module_license = QL_LGPL;
DLLEXPORT qore_module_init_t qore_module_init = ncurses_module_init;
DLLEXPORT qore_module_ns_init_t qore_module_ns_init = ncurses_module_ns_init;
DLLEXPORT qore_module_delete_t qore_module_delete = ncurses_module_delete;

Note that the module name (or the module's feature name) as given by `qore_module_name` is used to uniquely identify the feature provided by the module. Therefore if a module is loaded that provides feature "widget" and another module also claims to provided feature "widget", the second module cannot be loaded in the Qore library after the first has been loaded due to the duplicate feature name.

The `qore_module_api_major` and `qore_module_api_minor` variables are used to determine if the module corresponds to the API (and ABI) of the Qore library trying to load it.

## Module Functions

The module initialization function `qore_module_init()` will be run when the module is loaded by the Qore library. If any errors occur when initializing the module, a description should be returned as a QoreString pointer (the library will own the pointer and delete it later). If a non-zero pointer is returned by the `qore_module_init()` function, the feature will not be added to the Qore library and the module load will fail.

If the module provides any namespaces, classes or constants, they will be added on demand to QoreProgram objects by calling the module's `qore_module_ns_init()` function. In this case, the namespace additions should be initialized in the `qore_module_init()` function and copies should be provisioned in the `qore_module_ns_init()` function. In particular classes must not be created more than once, because a Qore class gets a unique ID assigned when it is created, and this ID must be unique in the entire Qore library.

Here are example functions from the ncurses module:

// this is the reference namespace for the ncurses module
static QoreNamespace NCNS("NCurses");
// this function is called when the module is loaded
QoreStringNode *ncurses_module_init()
{
// the NCurses reference namespace is set up here
NCNS.addSystemClass(initWindowClass());
NCNS.addSystemClass(initPanelClass());
init_constants(&NCNS); // here constants are added to the NCurses namespace
builtinFunctions.add("initscr", f_initscr, QDOM_TERMINAL_IO);
builtinFunctions.add("printw", f_printw, QDOM_TERMINAL_IO);
builtinFunctions.add("refresh", f_refresh, QDOM_TERMINAL_IO);
//... more builtin functions are added
return 0;
}
// this function is called when the Qore library needs to provision the NCurses namespace
// to a new QoreProgram object (or to a QoreProgram object that existed before the module
// was loaded by another QoreProgram object and then later requests the feature "ncurses")
void ncurses_module_ns_init(QoreNamespace *rns, QoreNamespace *qns)
{
// add the NCurses namespace as a subnamespace to the Qore namespace
qns->addInitialNamespace(NCNS.copy());
}
// this function is called when the module is deleted (when the qore library is closed)
// it should free all resources allocated in the module's initilization function
void ncurses_module_delete()
{
// calls endwin() if necessary
q_nc_init.close();
}