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<refentry xml:id="function.dl" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>dl</refname>
  <refpurpose>Loads a PHP extension at runtime</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <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>.
  </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>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>library</parameter></term>
     <listitem>
      <para>
       This 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>
       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;install-dir&gt;/lib/php/extensions/ &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>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <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>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>dl</function> examples</title>
    <programlisting role="php">
<![CDATA[
<?php
// Example loading an extension based on OS
if (!extension_loaded('sqlite')) {
    if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
        dl('php_sqlite.dll');
    } else {
        dl('sqlite.so');
    }
}

// Or, the PHP_SHLIB_SUFFIX constant is available as of PHP 4.3.0
if (!extension_loaded('sqlite')) {
    $prefix = (PHP_SHLIB_SUFFIX === 'dll') ? 'php_' : '';
    dl($prefix . 'sqlite.' . PHP_SHLIB_SUFFIX);
}
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>5.3.0</entry>
       <entry>
        This function now throws an E_DEPRECATED notice on all sapi's 
        except for CLI, CGI and Embed.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <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>
    As of PHP 5, the <function>dl</function> function is deprecated in every
    SAPI <emphasis>except</emphasis> <acronym>CLI</acronym>.
    Use <link linkend="ini.extension">Extension Loading Directives</link>
    method instead.
   </para>
  </note>
  <note>
   <para>
    Since PHP 6 this function is disabled in all SAPIs, except CLI, CGI and
    embed.
   </para>
  </note>
  <note>
   <para>
    <function>dl</function> is case sensitive on Unix platforms.
   </para>
  </note>
  &note.sm.disabled;
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><link linkend="ini.extension">Extension Loading Directives</link></member>
    <member><function>extension_loaded</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

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