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# dl

(PHP 3, PHP 4 )

dl -- Loads a PHP extension at runtime

## Description

bool 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()).

Example:

    if (!extension_loaded('gd')) {
        if (!dl('gd.so')) {
            exit;
        }
    }

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 `<php-install-directory>/lib/php/extension/<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: dl() is case sensitive on unix platforms.

See also Extension Loading Directives and extension_loaded().

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