function_exists
(PHP 4, PHP 5)
function_exists — Return TRUE if the given function has been defined
Description
bool function_exists
( string $function_name
)
Parameters
-
function_name
-
The function name, as a string.
Return Values
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().
Examples
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";
}
?>
Notes
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).
func_num_args
