define()

define() — Defines a named constant.

Built-in function of PHP 8.5. The manual lists it as available in PHP 4, PHP 5, PHP 7, PHP 8. This page is the reference card: signature, parameters and return value, plus the changelog and the example the manual provides.

Signature

define(string $constant_name, mixed $value, bool $case_insensitive = false): bool

Parameters

ParameterTypeWhat it takes
$constant_namestringThe name of the constant.
$valuemixedThe value of the constant.
$case_insensitiveboolIf set to true, the constant will be defined case-insensitive. The default behavior is case-sensitive; i.e. CONSTANT and Constant represent different values.

Return value

Returns true on success or false on failure.

Example

A runnable snippet:

define("CONSTANT", "Hello world."); echo CONSTANT; // outputs "Hello world." echo Constant; // outputs "Constant" and issues a notice. define("GREETING", "Hello you.", true); echo GREETING; // outputs "Hello you." echo Greeting; // outputs "Hello you." // Works as of PHP 7 define('ANIMALS', array( 'dog', 'cat', 'bird' )); echo ANIMALS[1]; // outputs "cat"

Changelog

VersionChange
8.1.0value can now be an object.
8.0.0Passing true to case_insensitive now emits an E_WARNING. Passing false is still allowed.
7.3.0case_insensitive has been deprecated and will be removed in version 8.0.0.

See also

defined(), constant()

All PHP 8.5 built-in functions

Reference card built from the PHP manual page define() (PHP documentation, CC BY 3.0). The page is generated from the manual, so the wording of the parameter and return value text follows php.net.