function_exists

(PHP 4, PHP 5)

function_exists — Return TRUE if the given function has been defined

说明

bool function_exists ( string $function_name )

Checks the list of defined functions, both built-in (internal) and user-defined, for function_name .

参数

function_name: The function name, as a string.

返回值

Returns TRUE if function_name exists and is a function, FALSE otherwise.

Note: This function will return FALSE for constructs, such as include_once() and echo().

范例

Example#1 function_exists() example


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

注释

Note: 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).

参见

method_exists()
is_callable()
get_defined_functions()


	PHP5中文手册 func_num_args get_defined_functions Function handling PHP Manual function_exists (PHP 4, PHP 5) function_exists — Return `TRUE` if the given function has been defined 说明 bool function_exists ( string `$function_name` ) Checks the list of defined functions, both built-in (internal) and user-defined, for `function_name` . 参数 `function_name` The function name, as a string. 返回值 Returns `TRUE` if `function_name` exists and is a function, `FALSE` otherwise. Note: This function will return `FALSE` for constructs, such as include_once() and echo(). 范例 Example#1 function_exists() example `<?php if (function_exists('imap_open')) { echo "IMAP functions are available.<br />\n"; } else { echo "IMAP functions are not available.<br />\n"; } ?>` 注释 Note: 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). 参见 method_exists() is_callable() get_defined_functions() func_num_args get_defined_functions Function handling PHP Manual