function_exists
(PHP 4, PHP 5, PHP 7, PHP 8)
function_exists — Return true if the given function has been defined
Description
function_exists(string
$function): bool
Checks the list of defined functions, both built-in (internal) and
user-defined, for function.
Parameters
-
function -
The function name, as a string.
Return Values
Returns true if function 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
<?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 a value can be called as a function from the current scope.
- 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
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