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
Pseudo-tipos e variáveis utilizados nesta documentação
Resource
[edit] Last updated: Fri, 28 Jun 2013
Resource
[edit] Last updated: Fri, 28 Jun 2013
NULL
O valor especial NULL representa
que a variável não tem valor. NULL é o único valor possível do tipo
NULL.
Nota: O tipo NULL foi incluído no PHP 4.
A variável é considerada null se:
-
ela foi assimilada com a constante
NULL. -
ela ainda não recebeu nenhum valor ainda.
-
ela foi apagada com unset().
Sintaxe
Há apenas um único valor do tipo null, e é
a palavra-chave case-insensitive NULL.
<?php
$var = NULL;
?>
Convertendo para NULL
Convertendo uma variável para null removerá a variável e apagar seu valor.
Pseudo-tipos e variáveis utilizados nesta documentação
Resource
[edit] Last updated: Fri, 28 Jun 2013
Resource
[edit] Last updated: Fri, 28 Jun 2013
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User Contributed Notes
NULL - [10 notes]
quickpick ¶
2 years ago
nl-x at bita dot nl ¶
5 years ago
Watch out. You can define a new constant with the name NULL with define("NULL","FOO");. But you must use the function constant("NULL"); to get it's value. NULL without the function call to the constant() function will still retrieve the special type NULL value.
Within a class there is no problem, as const NULL="Foo"; will be accessible as myClass::NULL.
poutri_j at epitech dot net ¶
7 years ago
if you declare something like this :
<?php
class toto
{
public $a = array();
public function load()
{
if ($this->a == null) // ==> the result is true
$a = other_func();
}
}
?>
be carefull, that's strange but an empty array is considered as a null variable
rizwan_nawaz786 at hotmail dot com ¶
8 years ago
Hi
Rizwan Here
Null is the Constant in PHP. it is use to assign a empty value to the variable like
$a=NULL;
At this time $a has is NULL or $a has no value;
When we declaire a veriable in other languages than that veriable has some value depending on the value of memory location at which it is pointed but in php when we declaire a veriable than php assign a NULL to a veriable.
foxdie_cs at hotmail dot com ¶
11 months ago
a quick note about the magic function __get() :
<?php
class Foo{
protected $bar;
public function __construct(){
$this->bar = NULL;
var_dump( $this->bar ); //prit 'NULL' but won't call the magic method __get()
unset( $this->bar );
var_dump( $this->bar ); //print 'GET bar' and 'NULL'
}
public function __get( $var ){ echo "GET " . $var; }
}
new Foo();
?>
Toycat ¶
1 month ago
Be careful using NULL together with namespaces. If a NULL constant is redefined in a namespace other than global, you will get unexpected results when comparing to NULL inside the namespace. Instead always use \NULL, \FALSE, and \TRUE when comparing. Otherwise it may lead to application failures and potential security issues where certain checks could be effectively disabled.
A simple example to demonstrate the behavior:
<?php
namespace RedefinedConstants {
// redefining global namespace constants has no effect
define('NULL', 'I am not global NULL!');
define('TRUE', 'I am not global TRUE!');
define('FALSE', 'I am not global FALSE!');
// redefining local namespace constants will work
define('RedefinedConstants\NULL', 'I am not NULL!', \TRUE);
define('RedefinedConstants\FALSE', 'I am not FALSE!', \TRUE);
define('RedefinedConstants\TRUE', 'I am not TRUE!', \TRUE);
var_dump(
NULL, \NULL, null, \null, Null, \Null,
FALSE, \FALSE, false, \false, False, \False,
TRUE, \TRUE, true, \true, True, \True
);
}
?>
ryan at trezshard dot com ¶
2 years ago
This simple shorthand seems to work for setting new variables to NULL:
<?php
$Var;
?>
The above code will set $Var to NULL
UPDATE: After further testing it appears the code only works in the global scope and does not work inside functions.
<?php
function Example(){
$Var;
var_dump($Var);
}
?>
Would not work as expected.
dward at maidencreek dot com ¶
11 years ago
Nulls are almost the same as unset variables and it is hard to tell the difference without creating errors from the interpreter:
<?php
$var = NULL;
?>
isset($var) is FALSE
empty($var) is TRUE
is_null($var) is TRUE
isset($novar) is FALSE
empty($novar) is TRUE
is_null($novar) gives an Undefined variable error
$var IS in the symbol table (from get_defined_vars())
$var CAN be used as an argument or an expression.
So, in most cases I found that we needed to use !isset($var) intead of is_null($var) and then set $var = NULL if the variable needs to be used later to guarantee that $var is a valid variable with a NULL value instead of being undefined.
cdcchen at hotmail dot com ¶
7 years ago
empty() is_null() !isset()
$var = "";
empty($var) is true.
is_null($var) is false.
!isset($var) is false.