defined

(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 'TEST' is the name of a constant named TEST */
if (defined('TEST')) {
    echo TEST;
}
?>

See Also

• define() - Defines a named constant
• constant() - Returns the value of a constant
• get_defined_constants() - Returns an associative array with the names of all the constants and their values
• function_exists() - Return TRUE if the given function has been defined
• The section on Constants