PHP - function_exists()

The function_exists() function can return true if a given function has been defined.

Syntax

bool function_exists( string $function_name )

The function_exists() function can check a list of defined functions, both built-in (internal) and user-defined for function_name. This function can return true, if function_name exist, or false otherwise.

Example

<?php
    $function_name = "fopen";
    if (function_exists($function_name) ) {
        echo "$function_name is enabled";
    } else {
       echo "$function_name is not enabled";
    }
?>

Output

fopen is enabled