(PHP 4, PHP 5, PHP 7, PHP 8)
define — Defines a named constant
Defines a named constant at runtime.
constant_nameThe 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, value must
be a scalar value (int,
float, string, bool, or
null). In PHP 7, array values are also accepted.
While 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.
CONSTANT and Constant represent
different values.
Defining case-insensitive constants is deprecated as of PHP 7.3.0.
As of PHP 8.0.0, only false is an acceptable value, passing
true will produce a warning.
Note:
Case-insensitive constants are stored as lower-case.
| 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. |
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)