PHP 8.3.4 Released!

define

(PHP 4, PHP 5, PHP 7, PHP 8)

defineDéfinit une constante

Description

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

Définit une constante à l'exécution.

Liste de paramètres

constant_name

Le nom de la constante.

Note:

Il est possible de définir avec define() des constantes avec des noms réservés ou même invalide, où leur valeur peuvent (seulement) être récupéré avec la fonction constant(). Cependant, faire ceci n'est pas recommandé.

value

La valeur de la constante. En PHP 5, value doit être une valeur scalaire (entier, nombre décimal, chaîne de caractères, booléen, ou null) En PHP 7, les valeurs tableau sont aussi autorisé. Il est techniquement possible de définir des constantes de type ressource, mais cela est fortement déconseillé, et peut causer des comportements inattendus.

Avertissement

Bien qu'il est techniquement possible de définir des constantes de type ressource, ceci est déconseillé et peut causer des comportements inattendus.

case_insensitive

S'il vaut true, le nom de la constante sera insensible à la casse : CONSTANT et Constant représentent des valeurs identiques.

Avertissement

Définir des constantes insensibles à la casse est obsolète à partir de PHP 7.3.0. À partir de PHP 8.0.0, seul false est une valeur acceptable, passer true produira un avertissement.

Note:

Les constantes insensibles à la casse sont stockées en minuscule.

Valeurs de retour

Cette fonction retourne true en cas de succès ou false si une erreur survient.

Historique

Version Description
8.0.0 Passer true à case_insensitive émet désormais une E_WARNING. Passer false est toujours autorisé.
7.3.0 case_insensitive est obsolète et sera supprimée dans la version 8.0.0.
7.0.0 Les valeurs array sont autorisées.

Exemples

Exemple #1 Définition d'une constante

<?php
define
("CONSTANT", "Bonjour le monde.");
echo
CONSTANT; // affiche "Bonjour le monde."
echo Constant; // affiche "Constant" et émet une alerte

define("GREETING", "Salut toi.", true);
echo
GREETING; // affiche "Salut toi."
echo Greeting; // affiche "Salut toi."

// Fonctionne depuis PHP 7
define('ANIMALS', array(
'chien',
'chat',
'oiseaux'
));
echo
ANIMALS[1]; // affiche "chat"

?>

Exemple #2 Constantes avec des Noms Réservés

Cet exemple illustre la possibilité de définir une constante avec le même nom qu'une constante magique. Puisque le comportement qui en résout porte à confusion, cette pratique n'est pas recommandée.

<?php
var_dump
(defined('__LINE__'));
var_dump(define('__LINE__', 'test'));
var_dump(constant('__LINE__'));
var_dump(__LINE__);
?>

L'exemple ci-dessus va afficher :

bool(false)
bool(true)
string(4) "test"
int(5)

Voir aussi

add a note

User Contributed Notes 17 notes

up
98
ravenswd at gmail dot com
9 years ago
Be aware that if "Notice"-level error reporting is turned off, then trying to use a constant as a variable will result in it being interpreted as a string, if it has not been defined.

I was working on a program which included a config file which contained:

<?php
define
('ENABLE_UPLOADS', true);
?>

Since I wanted to remove the ability for uploads, I changed the file to read:

<?php
//define('ENABLE_UPLOADS', true);
?>

However, to my surprise, the program was still allowing uploads. Digging deeper into the code, I discovered this:

<?php
if ( ENABLE_UPLOADS ):
?>

Since 'ENABLE_UPLOADS' was not defined as a constant, PHP was interpreting its use as a string constant, which of course evaluates as True.
up
24
@SimoEast on Twitter
6 years ago
Not sure why the docs omit this, but when attempting to define() a constant that has already been defined, it will fail, trigger an E_NOTICE and the constant's value will remain as it was originally defined (with the new value ignored).

(Guess that's why they're called "constants".)
up
26
danbettles at yahoo dot co dot uk
14 years ago
define() will define constants exactly as specified. So, if you want to define a constant in a namespace, you will need to specify the namespace in your call to define(), even if you're calling define() from within a namespace. The following examples will make it clear.

The following code will define the constant "MESSAGE" in the global namespace (i.e. "\MESSAGE").

<?php
namespace test;
define('MESSAGE', 'Hello world!');
?>

The following code will define two constants in the "test" namespace.

<?php
namespace test;
define('test\HELLO', 'Hello world!');
define(__NAMESPACE__ . '\GOODBYE', 'Goodbye cruel world!');
?>
up
1
Dale Landry
6 years ago
With php 7 you can now define arrays.

consider the following code:
<?php

define
( "EXPLENATIVES", [1 => "Foo Bar", 2 => "Fehw Bahr", 3 => "Foo Bahr", 4 => "Fooh Bar", 5 => "Fooh Bhar", 6 => "Foo Barr", 7 => "Foogh Bar", 8 => "Fehw Barr", 9 => "Fu bar", 10 => "Foo Bahr", 11 => "Phoo Bar", 12 => "Foo Bawr", 13 => "Phooh Baughr", 14 => "Foogan Bargan", 15 => "Foo Bahre", 16 => "Fu Bahar", 17 => "Fugh Bar", 18 => "Phou Baughr"]);

//set up define methods using mixed values; both array and non-array values
define("NAVBTNS", [EXPLENATIVES, "Nouns", "Verbs", "Adjectives"]);

//function to create a dropdown menu using the EXPLENATIVES array $btn=EXPLENATIVES=assoc_array

function construct_navbar_buttons(){

$btns = '<ul class="nav navbar-nav">';

foreach(
NAVBTNS as $button => $btn){
if(
is_array($btn)){
$btns .= '<li class="dropdown">
<a class="dropdown-toggle" data-toggle="dropdown" href="?id='
.$btn.'">
<i class="glyphicon glyphicon-user"></i> You Dare Say? <i class="glyphicon glyphicon-collapse-down"></i>
</a>
<ul class="dropdown-menu dropdown-user">'
;
foreach(
EXPLENATIVES as $key => $button){
$btns .= '<li><a href="#">'.$button.'</a></li>';
}
$btns .= '</ul>';
}else{
$btns .= '<li><a href="#">'.$btn.'</a></li>';
}
}

$btns .= '</ul>';
return
$btns;
}

Love this new implementation!

?>
up
1
chris at peeto dot net
13 years ago
The value of a constant can be the value of another constant.

<?php

define
("NEW_GOOD_NAME_CONSTANT", "I have a value");
define("OLD_BAD_NAME_CONSTANT", NEW_GOOD_NAME_CONSTANT);

echo
NEW_GOOD_NAME_CONSTANT; // current
echo OLD_BAD_NAME_CONSTANT; // legacy

?>
up
-1
Jamie
13 years ago
This is obvious, but easy to forget: if you include a file, the include file can only make use of constants already defined. For example:

<?php
define
("VEG","cabbage");
require(
"another file");
define("FRUIT","apple");

// "another file":
echo VEG; // cabbage
echo FRUIT; // FRUIT
?>
up
-2
me at mariusgerum dot de
5 years ago
You can define constants with variable names (works also with constant values or variables or array values or class properties and so on - as long it's a valid constant name).

<?php

# Define a constant and set a valid constant name as string value
define("SOME_CONSTANT", "NEW_CONSTANT");

# Define a second constant with dynamic name (the value from SOME_CONSTANT)
define(SOME_CONSTANT, "Some value");

# Output
echo SOME_CONSTANT; // prints "NEW_CONSTANT"
echo "<br>";
echo
NEW_CONSTANT; // prints "Some value"

?>

Needless to say that you'll lose your IDE support for refactoring and highlighting completely for such cases.
No clue why someone would / could actually use this but i thought it's worth mentioning.
up
-1
eparkerii at carolina dot rr dot com
15 years ago
Found something interesting. The following define:

<?php
define
("THIS-IS-A-TEST","This is a test");
echo
THIS-IS-A-TEST;
?>

Will return a '0'.

Whereas this:

<?php
define
("THIS_IS_A_TEST","This is a test");
echo
THIS_IS_A_TEST;
?>

Will return 'This is a test'.

This may be common knowledge but I only found out a few minutes ago.

[EDIT BY danbrown AT php DOT net: The original poster is referring to the hyphens versus underscores. Hyphens do not work in defines or variables, which is expected behavior.]
up
-3
axew3 at axew3 dot com
7 years ago
Php 7 - Define: "Defines a named constant at runtime. In PHP 7, array values are also accepted."

But prior PHP 7, you can maybe do this, to pass an array elsewhere using define:

$to_define_array = serialize($array);
define( "DEFINEANARRAY", $to_define_array );

... and so ...

$serialized = DEFINEANARRAY; // passing directly the defined will not work
$our_array = unserialize($serialized);

print_r($our_array);
up
-3
swisschocolate at cmail dot nu
8 years ago
I think worth mentioning is that define() appears to ignore invalid constant names.
One immediate implication of this seem to be that if you use an invalid constant name you have to use constant() to access it and obviously that you can't use the return value from define() to tell you whether the constant name used is invalid or not.

For example:
$name = '7(/!§%';
var_dump(define($name, "hello")); // outputs bool(true)
var_dump(constant($name)); // outputs string(5) "hello"
up
-4
Anonymous
6 years ago
There's an undocumented side-effect of setting the third parameter to true (case-insensitive constants): these constants can actually be "redefined" as case-sensitive, unless it's all lowercase (which you shouldn't define anyway).

The fact is that case-sensitive constants are stored as is, while case-insensitive constants are stored in lowercase, internally. You're still allowed to define other constants with the same name but capitalized differently (except for all lowercase).

<?php
// "echo CONST" prints 1, same as "echo const", "echo CoNst", etc.
define('CONST', 1, true);
echo CONST;
// Prints 1

define('CONST', 2);
echo CONST;
// Prints 2
echo CoNsT; // Prints 1
echo const; // Prints 1

// ** PHP NOTICE: Constant const already defined **
define('const', 3);
echo const;
// Prints 1
echo CONST; // Prints 2
?>

Why would you use this?

A third party plugin might attempt to define a constant for which you already set a value. If it's fine for them to set the new value, assuming you cannot edit the plugin, you could define your constant case-insensitive. You can still access the original value, if needed, by using any capitalization other than the one the plugin uses. As a matter of fact, I can't think of another case where you would want a case-insensitive constant...
up
-9
jan at webfontein dot nl
15 years ago
For translating with variables and define, take also a look on the constant() function.

Example :

<?php
define
('PAYMENT_IDEAL',"iDEAL Payment ( NL only )");
define('PAYMENT_MASTERCARD',"Mastercard Payment ( international )");

$payparam='MASTERCARD';

echo
constant("PAYMENT_$payparam");

// output :
// Mastercard Payment ( international )
?>
up
-8
phen at adnerdum dot org
12 years ago
To clear up a few thing:
Integers with 0 in front work. But since PHP (and many other languages) handle them as octal values, they're only allowed a range of 0-7:

<?php
define
('GOOD_OCTAL', 0700);
define('BAD_OCTAL', 0800);

print
GOOD_OCTAL;
print
'<br>';
print
BAD_OCTAL;
?>

Result:
448
0

---------------------------------------

Furthermore,

writing the constant name without the quotation-marks (as mentioned in the notes) throws an E_NOTICE and should be avoided!

<?php
define
(TEST, 'Throws an E_NOTICE');
?>

Result:
Notice: Use of undefined constant TEST - assumed 'TEST'
up
-8
David Spector
4 years ago
It may be worth stating that a define function must be executed before its global constant is referenced.

Example:

Abc();
define("TEST", 23);
function Abc()
{
echo TEST;
} // Abc

This code fails with a Notice-level message. TEST is treated here as being the string "TEST".
up
-8
ohcc at 163 dot com
3 years ago
A namespace constant can be defined using the define function, the constant defined this way is not global.

<?php
namespace WuXiancheng;
\define('China\Sichuan\Guangan\Yuechi\ZIP', 638300);
echo
ZIP; //Use of undefined constant ZIP
echo \China\Sichuan\Guangan\Yuechi\ZIP; // 638300
?>
up
-8
agneady at gmail dot nospam dot please dot com
2 years ago
If you happen to name your constant the same as a function name (either a built-in function or a user-defined one), PHP can handle this correctly based on context. For example:

<?php
function myfunc() {
return
'function output';
}

define('MYFUNC', 'constant value');

// note that function names are NOT case-sensitive
// so calling MYFUNC() is the same as calling myfunc()

echo 'MYFUNC(): ' . MYFUNC() . ', MYFUNC: ' . MYFUNC;
?>

Output:
MYFUNC(): function output, MYFUNC: constant value
up
-4
tux dot lector at gmail dot com
10 months ago
Since version 8 or 8.1, beat me if I recall any type of class
as defined constant value is perfectly valid.

Should You use it, I wouldn't know.
Most probably, referencing with such instances will fail badly.
But it might come handy for public and readonly classes.

<?php

define
('ClassInstance',
new class extends
\My\OtherClass {

private
bool $toggle = false;
private
float $real = 1.2345;
private ?
string $obj = null;

public function
__construct() {
$this-> privatemethod();
}

private function
privatemethod() {
$this-> obj = var_export ($this, true);
}

});

?>
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