glib/docs/reference/glib/tmpl/modules.sgml

<!-- ##### SECTION Title ##### -->
Dynamic Loading of Modules

<!-- ##### SECTION Short_Description ##### -->
portable method for dynamically loading 'plug-ins'.

<!-- ##### SECTION Long_Description ##### -->
<para>
These functions provide a portable way to dynamically load object files
(commonly known as 'plug-ins').
The current implementation supports all systems that provide
an implementation of dlopen() (e.g. Linux/Sun), as well as HP-UX via its
shl_load() mechanism, and Windows platforms via DLLs.
</para>
<para>
To use them you must first determine whether dynamic loading
is supported on the platform by calling g_module_supported().
If it is, you can open a module with g_module_open(),
find the module's symbols (e.g. function names) with g_module_symbol(),
and later close the module with g_module_close().
g_module_name() will return the file name of a currently opened module.
</para>
<para>
If any of the above functions fail, the error status can be found with
g_module_error().
</para>
<para>
The gmodule implementation features reference counting for opened modules,
and supports hook functions within a module which are called when the
module is loaded and unloaded (see #GModuleCheckInit and #GModuleUnload).
</para>
<para>
If your module introduces static data to common subsystems in the running
program, e.g. through calling g_quark_from_static_string ("my-module-stuff"),
it must ensure that it is never unloaded, by calling g_module_make_resident().
</para>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### STRUCT GModule ##### -->
<para>
The #GModule struct is an opaque data structure to represent a
<link linkend="glib-Dynamic-Loading-of-Modules">Dynamically-Loaded Module</link>.
It should only be accessed via the following functions.
</para>


<!-- ##### FUNCTION g_module_supported ##### -->
<para>
Checks if modules are supported on the current platform.
</para>

@Returns: TRUE if modules are supported.


<!-- ##### FUNCTION g_module_build_path ##### -->
<para>
A portable way to build the filename of a module. The platform-specific
prefix and suffix are added to the filename, if needed, and the result is
added to the directory, using the correct separator character.
</para>
<para>
The directory should specify the directory where the module can be found.
It can be NULL or an empty string to indicate that the module is in a standard
operating-system specific directory, though this is not recommended since the
wrong module may be found.
</para>
<para>
For example, calling g_module_build_path() on a Linux system with a directory
of "/lib" and a module_name of "mylibrary" will return "/lib/libmylibrary.so".
On a Windows system, using "\Windows" as the directory it will return
"\Windows\mylibrary.dll".
</para>

@directory: the directory where the module is. This can be NULL or the empty
string to indicate that the standard operating system-specific directories
will be used, though that is not recommended.
@module_name: the name of the module.
@Returns: the complete path of the module, including the standard library
prefix and suffix. This should be freed when no longer needed.


<!-- ##### FUNCTION g_module_open ##### -->
<para>
Opens a module.
If the module has already been opened, its reference count is incremented.
</para>

@file_name: the name of the file containing the module.
@flags: the flags used for opening the module. Currently this can be 0 or
G_MODULE_BIND_LAZY for lazy binding, where symbols are only bound when needed.
@Returns: a #GModule on success, or NULL on failure.


<!-- ##### ENUM GModuleFlags ##### -->
<para>
Flags passed to g_module_open().
G_MODULE_BIND_LAZY specifies that symbols are only resolved when needed.
The default action is to bind all symbols when the module is loaded.
(G_MODULE_BIND_LAZY is not supported on all platforms.)
</para>

@G_MODULE_BIND_LAZY: 
@G_MODULE_BIND_MASK: 

<!-- ##### FUNCTION g_module_symbol ##### -->
<para>
Gets a symbol pointer from a module.
</para>

@module: the module.
@symbol_name: the name of the symbol to find.
@symbol: returns the pointer to the symbol value.
@Returns: TRUE on success.


<!-- ##### FUNCTION g_module_name ##### -->
<para>
Gets the file name from a #GModule.
</para>

@module: the module.
@Returns: the file name of the module, or "main" if the module is the main
program itself.


<!-- ##### FUNCTION g_module_make_resident ##### -->
<para>
Ensures that a module will never be unloaded.
Any future g_module_close() calls on the module will be ignored.
</para>

@module: a module to make permanently resident.


<!-- ##### FUNCTION g_module_close ##### -->
<para>
Closes a module.
</para>

@module: the module to close.
@Returns: TRUE on success.


<!-- ##### FUNCTION g_module_error ##### -->
<para>
Gets a string describing the last module error.
</para>

@Returns: a string describing the last module error.


<!-- ##### USER_FUNCTION GModuleCheckInit ##### -->
<para>
Specifies the type of the module initialization function.
If a module contains a function named g_module_check_init() it is called
automatically when the module is loaded. It is passed the #GModule structure
and should return NULL on success or a string describing the initialization
error.
</para>

@module: the #GModule corresponding to the module which has just been loaded.
@Returns: NULL on success, or a string describing the initialization error.


<!-- ##### USER_FUNCTION GModuleUnload ##### -->
<para>
Specifies the type of the module function called when it is unloaded.
If a module contains a function named g_module_unload() it is called
automatically when the module is unloaded.
It is passed the #GModule structure.
</para>

@module: the module about to be unloaded.


<!-- ##### MACRO G_MODULE_EXPORT ##### -->
<para>
Used to declare functions exported by modules.
</para>



<!-- ##### MACRO G_MODULE_IMPORT ##### -->
<para>
Used to declare functions imported from modules.
</para>