PHP Manual
Prev |  | Next

# defined

(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; } ?>`

> 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().

See also define(), constant(), get_defined_constants(), function_exists(), and the section on Constants.

Prev | Home | Next
define | Up | die