Introduction to libgmodule

libgmodule has APIs that provide a portable method for dynamically loading 'plug-ins' or, in other words, DLLs. Any program that wants to dynamically load modules must be linked to libgmodule .

In order to use the libgmodule APIs, the user must check whether dynamic loading of DLLs is supported by the platform by using the g_module_supported() API which returns TRUE if the dynamic loading of modules is supported. P.I.P.S. provides the implementation of libdl , where dynamic loading of modules is supported, but to write code which runs across platforms the user must do a check before using the libgmodule APIs.

If the dynamic loading of DLLs is supported, use g_module_open() to open the module. It takes the name of the module as the first argument and the flags as the second argument.

Note: G_MODULE_BIND_LOCAL is the only flag currently supported. The other flags are not supported. If the user specifies any other flag, the module is loaded using the flag G_MODULE_BIND_LOCAL and not by the user-specified flag.

GModule * g_module_open(const gchar *file_name, GModuleFlags flags);

  • file_name : The name of the file containing the module.

  • flags : The flags used for opening the module.

Once the module is opened, the user can find the module symbols (for example,. function names) using the function

g_module_symbol() .

gboolean g_module_symbol (GModule *module, const gchar *symbol_name, gpointer *symbol);

  • *module : This is a pointer returned when a module is opened using g_module_open() .

  • symbol_name : This is the ordinal number of the symbol that one wants to open. There is a difference between Symbian GLib and OSS GLib; as in Linux the symbol_name is the name of the symbol and not a number. The ordinal number must be passed as a string and not a number.

  • symbol : This is the pointer to the symbol value

The GModule can be closed by using the g_module_close() API. This API returns TRUE if it successfully closed the module; else it returns FALSE.

gboolean g_module_close(GModule *module);

  • *module The GModule to close.

The following example code explains the usage of the libgmodule APIs. It opens a module libmoduletestplugin_a.dll and uses its gplugin_a_func1() API which is ordinal number 1. Finally, the module is closed.

      #include <gmodule.h>
#include <glib.h>
typedef int (*SimpleFunc) (void);

int main()
  GModule *module = NULL;
  gpointer func;
  SimpleFunc f_a;
  int retVal;
  if (!g_module_supported())
        g_print ("Dynamic Opening of modules is not supported");
        return 1;
  /* G_MODULE_BIND_LAZY is overridden and the module is opened with
  module = g_module_open("libmoduletestplugin_a.dll",G_MODULE_BIND_LAZY);
  // 1 is the ordinal number for gplugin_a_func1
  if(module && g_module_symbol(module, "1" ,&func)) 	
        f_a = (SimpleFunc)func;
        retVal = f_a();	
        g_print("Function at ordinal number 1 of module libgmodule_a returns %d",retVal);
        g_print("Error quering symbol at ordinal number 1");
        return 1;
  return 0;

See the Libgmodule APIs section in Differences between OSS and Symbian GLib for more details about libgmodule limitations in the Symbian GLib implementation.