php-doc-en/reference/info/functions/dl.xml

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  <refentry id="function.dl">
   <refnamediv>
    <refname>dl</refname>
    <refpurpose>Loads a PHP extension at runtime</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <methodsynopsis>
     <type>int</type><methodname>dl</methodname>
     <methodparam><type>string</type><parameter>library</parameter></methodparam>
    </methodsynopsis>
    <para>
     Loads the PHP extension given by the parameter
     <parameter>library</parameter>. The <parameter>library</parameter>
     parameter is <emphasis>only</emphasis> the filename of the extension to
     load which also depends on your platform. For example, the <link
     linkend="ref.sockets">sockets</link> extension (if compiled as a shared
     module, not the default!) would be called <filename>sockets.so</filename>
     on unix platforms whereas it is called
     <filename>php_sockets.dll</filename> on the windows platform.
    </para>
    <para>
     &return.success; If the functionality of loading modules is not available
     (see Note) or has been disabled (either by turning it off
     <literal>enable_dl</literal> or by enabling &safemode;
     in &php.ini;) an <constant>E_ERROR</constant> is emitted
     and execution is stopped. If <function>dl</function> fails because the
     specified library couldn't be loaded, in addition to &false; an
     <constant>E_WARNING</constant> message is emitted.
    </para>
    <para>
     Use <function>extension_loaded</function> to test whether a given
     extension is already available or not. This works on both built-in
     extensions and dynamically loaded ones (either through &php.ini;
     or <function>dl</function>).
    </para>
    <example>
     <title><function>dl</function> example</title>
     <programlisting role="php">
<![CDATA[
if (!extension_loaded('gd')) {
    if (!dl('gd.so')) {
        exit;
    }
}
]]>
     </programlisting>
    </example>
    <para>
     The directory where the extension is loaded from depends on your
     platform:
    </para>
    <para>
     Windows - If not explicitly set in the &php.ini;, the extension is
     loaded from <filename>c:\php4\extensions\</filename> by default.
    </para>
    <para>
     Unix - If not explicitly set in the &php.ini;, the default extension
     directory depends on
     <itemizedlist>
      <listitem>
       <simpara>
        whether PHP has been built with <literal>--enable-debug</literal> or
        not
       </simpara>
      </listitem>
      <listitem>
       <simpara>
        whether PHP has been built with (experimental) ZTS (Zend Thread Safety)
        support or not
       </simpara>
      </listitem>
      <listitem>
       <simpara>
        the current internal <literal>ZEND_MODULE_API_NO</literal> (Zend
        internal module API number, which is basically the date on which a
        major module API change happened, e.g. <literal>20010901</literal>)
       </simpara>
      </listitem>
     </itemizedlist>
     Taking into account the above, the directory then defaults to
     <literal>&lt;php-install-directory&gt;/lib/php/extension/&lt;debug-or-not&gt;-&lt;zts-or-not&gt;-ZEND_MODULE_API_NO</literal>,
     e.g.
     <filename>/usr/local/php/lib/php/extensions/debug-non-zts-20010901</filename>
     or
     <filename>/usr/local/php/lib/php/extensions/no-debug-zts-20010901</filename>.
    </para>
    <note>
     <para>
      <function>dl</function> is <emphasis>not</emphasis> supported in
      multithreaded Web servers. Use the <literal>extensions</literal>
      statement in your &php.ini; when operating under such
      an environment. However, the <literal>CGI</literal> and
      <literal>CLI</literal> build are <emphasis role="strong">not</emphasis>
      affected !
     </para>
    </note>
    <note>
     <para>
      <function>dl</function> is case sensitive on unix platforms.
     </para>
    </note>
    <para>
     See also
     <link linkend="ini.extension">Extension Loading Directives</link>
     and <function>extension_loaded</function>.
    </para>
   </refsect1>
  </refentry>

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