Note: empty array is converted to null by non-strict equal '==' comparison. Use is_null() or '===' if there is possible of getting empty array.
$a = array();
$a == null <== return true
$a === null < == return false
is_null($a) <== return false
NULL
La valeur spéciale null représente une variable sans valeur. null est
la seule valeur possible du type null.
Une variable est considérée comme null si :
-
elle s'est vue assigner la constante
null. -
elle n'a pas encore reçu de valeur.
-
elle a été effacée avec la fonction unset().
Syntaxe
Il y a une seule valeur de type null, et c'est la constante
insensible à la casse null.
<?php
$var = NULL;
?>
Transtyper vers null
Avertissement
Cette fonctionnalité est OBSOLÈTE à partir de PHP 7.2.0. Dépendre de cette fonctionnalité est fortement déconseillé.
Transtyper une variable vers null en utilisant
la syntaxe (unset) $var n'effacera pas
la variable, ni écrasera sa valeur. Ca ne fera que retourner
la valeur null.
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User Contributed Notes 5 notes
quickpick ¶
13 years ago
hydrogen at live dot in ¶
3 years ago
I would like to add for clarification that:
$x=NULL;
--$x;
// $x is still NULL.
// Decrementing NULL, using Decrement Operator, gives NULL.
$x-=1;
// $x is now int(-1).
// This actually decrements value by 1.
On the other hand, Incrementation works simply as expected.
Hope this helps :)
Hayley Watson ¶
6 years ago
NULL is supposed to indicate the absence of a value, rather than being thought of as a value itself. It's the empty slot, it's the missing information, it's the unanswered question. It's not a jumped-up zero or empty set.
This is why a variable containing a NULL is considered to be unset: it doesn't have a value. Setting a variable to NULL is telling it to forget its value without providing a replacement value to remember instead. The variable remains so that you can give it a proper value to remember later; this is especially important when the variable is an array element or object property.
It's a bit of semantic awkwardness to speak of a "null value", but if a variable can exist without having a value, the language and implementation have to have something to represent that situation. Because someone will ask. If only to see if the slot has been filled.
