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(PHP 3, PHP 4, PHP 5)

defined --  Checks whether a given named constant exists

Description

bool defined ( string name )

Returns TRUE if the named constant given by name has been defined, FALSE otherwise.

Example 1. Checking Constants

<?php
/* Note the use of quotes, this is important.  This example is checking 
 * if the string 'CONSTANT' is the name of a constant named CONSTANT */
if (defined('CONSTANT')) {
    echo CONSTANT;
}
?>

Related Function(s)

isset()

function_exists()

define()

constant()

get_defined_constants()