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function_exists

(PHP 3 >= 3.0.7, PHP 4, PHP 5)

function_exists --  Return TRUE if the given function has been defined

Description

bool function_exists ( string function_name )

Checks the list of defined functions, both built-in (internal) and user-defined, for function_name . 如果成功则返回 TRUE ，失败则返回 FALSE 。

<?php
if ( function_exists ( 'imap_open' )) {
    echo "IMAP functions are available.<br />\n" ;
} else {
    echo "IMAP functions are not available.<br />\n" ;
}
?>

Note that a function name may exist even if the function itself is unusable due to configuration or compiling options (with the image functions being an example). Also note that function_exists() will return FALSE for constructs, such as include_once() and echo() .

See also method_exists() , is_callable() and get_defined_functions() .

后退 起点 前进
func_num_args 上一级 get_defined_functions