PHP Manual: defined

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defined

(PHP 3, PHP 4, PHP 5)

defined -- Checks whether a given named constant exists

Description

bool defined ( string name )

Checks whether the given constant exists and is defined.

Note: If you want to see if a variable exists, use isset() as defined() only applies to constants. If you want to see if a function exists, use function_exists().

Parameters

name: The constant name.

Return Values

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

Examples

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;
}
?>

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