function_exists
(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.
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).
See Also
- method_exists() - Checks if the class method exists
- is_callable() - Verify that the contents of a variable can be called as a function
- get_defined_functions() - Returns an array of all defined functions