(PHP 4, PHP 5, PHP 7)
function_exists — Return true
if the given function has been defined
function_exists ( string $function_name ) : bool
Checks the list of defined functions, both built-in (internal) and user-defined, for function_name
.
function_name
The function name, as a string.
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.
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"; } ?>
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).
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Licensed under the Creative Commons Attribution License v3.0 or later.
https://www.php.net/manual/en/function.function-exists.php