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# dl

(PHP 3, PHP 4 , PHP 5)

dl -- Loads a PHP extension at runtime

## Description

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.

成功回傳`TRUE`失敗回傳`FALSE`。 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 安全模式 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()).

The dl() function is deprecated as of PHP 5. Use Extension Loading Directives method instead.

範例 1. dl() examples

`<?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); } ?>`

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`.

> 注: 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 !

> 注: dl() is case sensitive on Unix platforms.

> 注: ???

See also Extension Loading Directives and extension_loaded().

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