define
I found something out: defined() becomes probably false if a reference gets lost.
<?php
session_start(); // $_SESSION created
define('SESSION_BACKUP', $_SESSION);
if (defined('SESSION_BACKUP')) echo 'A';
session_unset(); // $_SESSION destroyed
if (defined('SESSION_BACKUP')) echo 'B';
?>
You will see "A", but not "B".
defined
(PHP 4, PHP 5)
defined — Vérifie l'existence d'une constante
Description
bool defined
( string $name
)
Vérifie l'existence d'une constante.
Note: Si vous voulez vérifier si une variable existe, utilisez isset() car defined() ne s'applique qu'aux constants. Si vous voulez voir si une fonction existe, utilisez function_exists().
Liste de paramètres
- name
-
Le nom de la constante.
Valeurs de retour
Retourne TRUE si le nom de la constante fournie par le paramètre name a été définie, FALSE sinon.
Exemples
Exemple #1 Vérifier la présence de constantes avec defined()
<?php
/* Notez que le nom de la constante est entre guillemets. Cet exemple vérifie
* si la chaîne 'TEST' est le nom de la constante nommée TEST */
if (defined('TEST')) {
echo TEST;
}
?>
Voir aussi
- define() - Définit une constante
- constant() - Retourne la valeur d'une constante
- get_defined_constants() - Retourne la liste des constantes et leurs valeurs
- function_exists() - Indique si une fonction est définie
- La section sur les constantes
add a note
User Contributed Notesdefined
info at daniel-marschall dot de
11-Jul-2009 08:51
11-Jul-2009 08:51
tris+php at tfconsulting dot com dot au
27-Mar-2009 02:40
27-Mar-2009 02:40
Before using defined() have a look at the following benchmarks:
true 0.65ms
$true 0.69ms (1)
$config['true'] 0.87ms
TRUE_CONST 1.28ms (2)
true 0.65ms
defined('TRUE_CONST') 2.06ms (3)
defined('UNDEF_CONST') 12.34ms (4)
isset($config['def_key']) 0.91ms (5)
isset($config['undef_key']) 0.79ms
isset($empty_hash[$good_key]) 0.78ms
isset($small_hash[$good_key]) 0.86ms
isset($big_hash[$good_key]) 0.89ms
isset($small_hash[$bad_key]) 0.78ms
isset($big_hash[$bad_key]) 0.80ms
PHP Version 5.2.6, Apache 2.0, Windows XP
Each statement was executed 1000 times and while a 12ms overhead on 1000 calls isn't going to have the end users tearing their hair out, it does throw up some interesting results when comparing to if(true):
1) if($true) was virtually identical
2) if(TRUE_CONST) was almost twice as slow - I guess that the substitution isn't done at compile time (I had to double check this one!)
3) defined() is 3 times slower if the constant exists
4) defined() is 19 TIMES SLOWER if the constant doesn't exist!
5) isset() is remarkably efficient regardless of what you throw at it (great news for anyone implementing array driven event systems - me!)
May want to avoid if(defined('DEBUG'))...
phrank
30-Jan-2009 09:17
30-Jan-2009 09:17
@ ndove at cox dot net
But you receive a Fatal error 'Undefined class constant' if the constant is not defined.:-)
reachmike at hotpop dot com
01-Dec-2008 06:17
01-Dec-2008 06:17
You may find that if you use <?= ?> to dump your constants, and they are not defined, depending on your error reporting level, you may not display an error and, instead, just show the name of the constant. For example:
<?= TEST ?>
...may say TEST instead of an empty string like you might expect. The fix is a function like this:
<?php
function C(&$constant) {
$nPrev1 = error_reporting(E_ALL);
$sPrev2 = ini_set('display_errors', '0');
$sTest = defined($constant) ? 'defined' : 'not defined';
$oTest = (object) error_get_last();
error_reporting($nPrev1);
ini_set('display_errors', $sPrev2);
if ($oTest->message) {
return '';
} else {
return $constant;
}
}
?>
And so now you can do:
<?= C(TEST) ?>
If TEST was assigned with define(), then you'll receive the value. If not, then you'll receive an empty string.
Please post if you can do this in fewer lines of code or do something more optimal than toggling the error handler.
Anonymous
21-Oct-2008 03:36
21-Oct-2008 03:36
Nice one, here's may addition:
index.php:
<?php
// Main stuff here
define('SITE_IN', 1);
include "x.php";
?>
x.php:
<?php
if (!defined('SITE_IN') or !constant('SITE_IN')) die('Direct access not allowed!');
?>
A bit of extra protection, a bit paranoid yes, it's good to be :)
daniel at neville dot tk
14-Jul-2008 05:48
14-Jul-2008 05:48
My preferred way of checking if a constant is set, and if it isn't - setting it (could be used to set defaults in a file, where the user has already had the opportunity to set their own values in another.)
<?php
defined('CONSTANT') or define('CONSTANT', 'SomeDefaultValue');
?>
Dan.
admin at rune-city dot com
12-Jul-2008 11:39
12-Jul-2008 11:39
If you wish to protect files from direct access I normally use this:
index.php:
<?php
// Main stuff here
define('SITE_IN', 1);
include "x.php";
?>
x.php:
<?php
if (!defined('SITE_IN')) die('Direct access not allowed!');
?>
Shaun H
28-Mar-2008 07:30
28-Mar-2008 07:30
I saw that PHP doesn't have an enum function so I created my own. It's not necessary, but can come in handy from time to time.
<?php
function enum()
{
$args = func_get_args();
foreach($args as $key=>$arg)
{
if(defined($arg))
{
die('Redefinition of defined constant ' . $arg);
}
define($arg, $key);
}
}
enum('ONE','TWO','THREE');
echo ONE, ' ', TWO, ' ', THREE;
?>
Joel
20-Aug-2007 12:35
20-Aug-2007 12:35
If your constants don't show up in your included or required files, then you probably have php safe mode turned on!
I ran into this problem, I forgot to turn of safe mode when I was creating a new site.
ndove at cox dot net
28-Jan-2005 03:20
28-Jan-2005 03:20
In PHP5, you can actually use defined() to see if an object constant has been defined, like so:
<?php
class Generic
{
const WhatAmI = 'Generic';
}
if (defined('Generic::WhatAmI'))
{
echo Generic::WhatAmI;
}
?>
Thought it may be useful to note.
-Nick
Craig at chatspike dot net
30-Nov-2003 07:57
30-Nov-2003 07:57
This can be useful if you want to protect pages which get included from outsiders eyes, on your mail page (the page viewable by people) put define("X", null); then on all your other pages, you can then do something like:
<?php
if (!defined("X")) {
echo "You Cannot Access This Script Directly, Have a Nice Day.";
exit();
}
?>
And your page is a good as protected :)