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<concept id="GUID-01E7AE98-024C-4119-87D0-5BB9D53DA119" xml:lang="en"><title>Introduction

to <codeph>libgmodule</codeph></title><shortdesc><codeph>libgmodule</codeph> 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 <codeph>libgmodule</codeph>.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>In order to use the <codeph>libgmodule</codeph> APIs, the user must check

whether dynamic loading of DLLs is supported by the platform by using the <codeph>g_module_supported()</codeph> API

which returns TRUE if the dynamic loading of modules is supported. P.I.P.S.

provides the implementation of <codeph>libdl</codeph>, where dynamic loading

of modules is supported, but to write code which runs across platforms the

user must do a check before using the <codeph>libgmodule</codeph> APIs.  </p>

<p>If the dynamic loading of DLLs is supported, use <codeph>g_module_open()</codeph> to

open the module. It takes the name of the module as the first argument and

the flags as the second argument.</p>

<note><codeph>G_MODULE_BIND_LOCAL</codeph> 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 <codeph>G_MODULE_BIND_LOCAL</codeph> and not

by the user-specified flag.</note>

<p><b><codeph>GModule * g_module_open(const gchar *file_name, GModuleFlags

flags);</codeph></b></p>

<ul>

<li><p><b><codeph>file_name</codeph>:</b> The name of the file containing

the module.</p></li>

<li><p><b><codeph>flags</codeph>:</b> The flags used for opening the module. </p></li>

</ul>

<p>Once the module is opened, the user can find the module symbols (for example,.

function names) using the function </p>

<p><codeph>g_module_symbol()</codeph>.</p>

<p><b><codeph>gboolean g_module_symbol (GModule *module, const gchar *symbol_name,

gpointer *symbol);</codeph></b></p>

<ul>

<li><p><b><codeph>*module</codeph>:</b> This is a pointer returned when a

module is opened using <codeph>g_module_open()</codeph>.</p></li>

<li><p><b><codeph>symbol_name</codeph>:</b> 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 <codeph>symbol_name</codeph> is the name of

the symbol and not a number. The ordinal number must be passed as a string

and not a number.</p></li>

<li><p><b><codeph>symbol</codeph>:</b> This is the pointer to the symbol value </p></li>

</ul>

<p>The <codeph>GModule</codeph> can be closed by using the <codeph>g_module_close()</codeph> API.

This API returns TRUE if it successfully closed the module; else it returns

FALSE.</p>

<p><b><codeph>gboolean g_module_close(GModule *module);</codeph></b></p>

<ul>

<li><p><b><codeph>*module</codeph></b> The <codeph>GModule</codeph> to close. </p></li>

</ul>

<p>The following example code explains the usage of the <codeph>libgmodule</codeph> APIs.

It opens a module <filepath>libmoduletestplugin_a.dll</filepath> and uses

its <codeph>gplugin_a_func1()</codeph> API which is ordinal number 1. Finally,

the module is closed.</p>

<codeblock xml:space="preserve">#include &lt;gmodule.h&gt;

#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

   * flag G_MODULE_BIND_LOCAL

   */

  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);

  }

  else

  {

        g_print("Error quering symbol at ordinal number 1");

        return 1;

  }

  return 0;

}</codeblock>

<p>See the <b>Libgmodule APIs</b> section in <xref href="GUID-4ADD8234-4AFD-4E80-94A4-AC018FE83276.dita">Differences

between OSS and Symbian GLib</xref> for more details about <codeph>libgmodule</codeph> limitations

in the Symbian GLib implementation.  </p>