Php/docs/function.function-exists
function_exists
(PHP 4, PHP 5, PHP 7)
function_exists — Return TRUE if the given function has been defined
Description
function_exists
( string $function_name
) : bool
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
FALSEfor constructs, such as include_once and echo.
Examples
Example #1 function_exists() example
<?phpif (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
- class_exists() - Checks if the class has been defined
- extension_loaded() - Find out whether an extension is loaded
