defined

(PHP 4, PHP 5, PHP 7, PHP 8)

definedChecks whether a given named constant exists

Description

defined(string $constant_name): bool

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

constant_name

The constant name.

Return Values

Returns true if the named constant given by constant_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