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PHP defined() Function

Complete PHP Misc Reference

Definition and Usage

The defined() function checks whether a constant exists.

Returns TRUE if the constant exists, or FALSE otherwise.

Syntax

defined(name)

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

Example

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

The output of the code above will be: