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
Il valore speciale null rappresenta una variable senza valore. null è il
solo valore possibile del tipo null.
Una variabile è null se:
-
le è stato assegnata la costante
null. -
non le è stato ancora assegnato un valore.
-
è stata cancellata con la funzione unset().
Syntax
Esiste solo un valore di tipo null, la costante
null, che è invariante, sia essa in maiuscolo o in minuscolo.
<?php
$var = NULL;
?>Casting a null
Effettuare il casting di una variabile a null usando (unset) $var
non rimuove la variabile, né cancella il valore.
Non fa altro che restituire un valore null.
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User Contributed Notes 2 notes
quickpick ¶
13 years ago
Hayley Watson ¶
7 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.
