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Last updated: Tue, 19 Sep 2006


(PHP 3, PHP 4, PHP 5)

dl -- Loads a PHP extension at runtime


int dl ( string library )

Loads the PHP extension given by the parameter library. The library parameter is only the filename of the extension to load which also depends on your platform. For example, the sockets extension (if compiled as a shared module, not the default!) would be called sockets.so on Unix platforms whereas it is called php_sockets.dll on the Windows platform.

Returns TRUE on success or FALSE on failure. If the functionality of loading modules is not available (see Note) or has been disabled (either by turning it off enable_dl or by enabling safe mode in php.ini) an E_ERROR is emitted and execution is stopped. If dl() fails because the specified library couldn't be loaded, in addition to FALSE an E_WARNING message is emitted.

Use extension_loaded() 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 dl()).

As of PHP 5, the dl() function is deprecated in every SAPI except CLI. Use Extension Loading Directives method instead.

Example 1. dl() examples

// Example loading an extension based on OS
if (!extension_loaded('sqlite')) {
    if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
    } else {

// 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);

The directory where the extension is loaded from depends on your platform:

Windows - If not explicitly set in the php.ini, the extension is loaded from c:\php4\extensions\ by default.

Unix - If not explicitly set in the php.ini, the default extension directory depends on

  • whether PHP has been built with --enable-debug or not

  • whether PHP has been built with (experimental) ZTS (Zend Thread Safety) support or not

  • the current internal ZEND_MODULE_API_NO (Zend internal module API number, which is basically the date on which a major module API change happened, e.g. 20010901)

Taking into account the above, the directory then defaults to <install-dir>/lib/php/extensions/ <debug-or-not>-<zts-or-not>-ZEND_MODULE_API_NO, e.g. /usr/local/php/lib/php/extensions/debug-non-zts-20010901 or /usr/local/php/lib/php/extensions/no-debug-zts-20010901.

Note: dl() is not supported in multithreaded Web servers. Use the extensions statement in your php.ini when operating under such an environment. However, the CGI and CLI build are not affected !

Note: Since PHP 6 this function is disabled in all SAPIs, except CLI, CGI and embed.

Note: dl() is case sensitive on Unix platforms.

Note: This function is disabled in safe mode.

See also Extension Loading Directives and extension_loaded().

Last updated: Tue, 19 Sep 2006