PHP defined() Function

Check if a constant exists:

<?php
define("GREETING","Hello you! How are you today?");
echo defined("GREETING");
?>

Definition and Usage

The defined() function checks whether a constant exists.

defined( name)

Parameter	Description
name	Required. Specifies the name of the constant to check

Return Value:	Returns TRUE if the constant exists, or FALSE otherwise
PHP Version:	4+