The special null value represents a variable with no value. null is the only possible value of type null.
A variable is considered to be null if:
it has been assigned the constant null.
it has not been set to any value yet.
it has been unset().
Syntax
There is only one value of type null, and that is the case-insensitive constant null.
See also the functions is_null() and unset().
Casting to null
Warning
This feature has been DEPRECATED as of PHP 7.2.0, and REMOVED as of PHP 8.0.0. Relying on this feature is highly discouraged.
Casting a variable to null using (unset) $var will not remove the variable or unset its value. It will only return a null value.
quickpick ¶
11 years ago
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
mattias at kregert dot se ¶
1 year ago
Note that NULL works like a magic object with any attribute you can name, but they are all NULL:
foreach ( [ null, null ] as $person ) {
$friends[] = [ 'Name'=>$person['name'], 'Phone'=>$person['cell'] ];
}
print_r($friends);
Array
(
[0] => Array
(
[Name] =>
[Phone] =>
)
[1] => Array
(
[Name] =>
[Phone] =>
)
)
This means that:
* NULL == NULL['foo']['bar']['whatever']
This can be slightly confusing if you accidentally slip a NULL into an array of other items.
Hayley Watson ¶
4 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.
Anonymous ¶
4 years ago
Note: Non Strict Comparison '==' returns bool(true) for
null == 0 <-- returns true
Use Strict Comparison Instead
null === 0 <-- returns false
hydrogen at live dot in ¶
1 year 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 :)
Mojo ¶
1 year ago
Pay attention then using operator -- on NULL values:
$x = null;
--$x; // $x is NULL
$x--; // still NULL
$x -= 1; // $x is -1
On other side for ++ everything works fine:
$x = null;
++$x; // $ix is 1