define
(PHP 4, PHP 5, PHP 7, PHP 8)
define — Defines a named constant
Description
Defines a named constant at runtime.
Parameters
-
constant_name -
The name of the constant.
Note:
It is possible to define() constants with reserved or even invalid names, whose value can (only) be retrieved with constant(). However, doing so is not recommended.
-
value -
The value of the constant. In PHP 5,
valuemust be a scalar value (int, float, string, bool, ornull). In PHP 7, array values are also accepted.WarningWhile it is possible to define resource constants, it is not recommended and may cause unpredictable behavior.
-
case_insensitive -
If set to
true, the constant will be defined case-insensitive. The default behavior is case-sensitive; i.e.CONSTANTandConstantrepresent different values.WarningDefining case-insensitive constants is deprecated as of PHP 7.3.0. As of PHP 8.0.0, only
falseis an acceptable value, passingtruewill produce a warning.Note:
Case-insensitive constants are stored as lower-case.
Return Values
Returns true on success or false on failure.
Changelog
| Version | Description |
|---|---|
| 8.0.0 |
Passing true to case_insensitive now emits an E_WARNING. Passing false is still allowed.
|
| 7.3.0 |
case_insensitive has been deprecated and will be removed in version 8.0.0.
|
| 7.0.0 | array values are allowed. |
Examples
Example #1 Defining Constants
<?php
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"
?>
Example #2 Constants with Reserved Names
This example illustrates the possibility to define a constant with the same name as a magic constant. Since the resulting behavior is obviously confusing, it is not recommended to do this in practise, though.
<?php
var_dump(defined('__LINE__'));
var_dump(define('__LINE__', 'test'));
var_dump(constant('__LINE__'));
var_dump(__LINE__);
?>
The above example will output:
bool(false) bool(true) string(4) "test" int(5)
See Also
- defined() - Checks whether a given named constant exists
- constant() - Returns the value of a constant
- The section on Constants
