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
NULO
El valor especial null representa una variable sin valor. null es el
único valor posible del tipo null.
Una variable es considerada null si:
-
se le ha asignado la constante
null. -
no se le ha asignado un valor todavía.
-
se ha destruido con unset().
Sintaxis
No hay más que un valor de tipo null, y es la
constante null insensible a mayúsculas/minúsculas.
<?php
$var = NULL;
?>La conversión a null
Advertencia
Esta característica ha sido declarada OBSOLETA a partir de PHP 7.2.0. Su uso está totalmente desaconsejado.
Convertir una variable a null usando (unset) $var
no eliminará la variable ni destruirá su valor.
Sólo retornará un valor null.
add a note
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.
