Misc. Functions
PHP Manual

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
  • constant
  • get_defined_constants
  • function_exists
  • The section on Constants