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A little speed test:
<?php
$v = NULL;
$s = microtime(TRUE);
for($i=0; $i<1000; $i++) {
is_null($v);
}
print microtime(TRUE)-$s;
print "<br>";
$s = microtime(TRUE);
for($i=0; $i<1000; $i++) {
$v===NULL;
}
print microtime(TRUE)-$s;
?>
Results:
0.017982006072998
0.0005950927734375
Using "===" is 30x quicker than is_null().
NULL
The special NULL value represents a variable with no value. NULL is the only possible value of type NULL.
Note: The null type was introduced in PHP 4.
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 keyword NULL.
<?php
$var = NULL;
?>
Casting to NULL
Casting a variable to null will remove the variable and unset its value.
add a note
User Contributed NotesNULL
james
20-Sep-2007 05:25
20-Sep-2007 05:25
nl-x at bita dot nl
09-Jul-2007 07:33
09-Jul-2007 07:33
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.
cdcchen at hotmail dot com
26-May-2006 05:17
26-May-2006 05:17
empty() is_null() !isset()
$var = "";
empty($var) is true.
is_null($var) is false.
!isset($var) is false.
06-Jan-2006 10:51
// Difference between "unset($a);" and "$a = NULL;" :
<?php
// unset($a)
$a = 5;
$b = & $a;
unset($a);
print "b $b "; // b 5
// $a = NULL; (better I think)
$a = 5;
$b = & $a;
$a = NULL;
print "b $b "; // b
print(! isset($b)); // 1
?>
poutri_j at epitech dot net
26-Jul-2005 01:56
26-Jul-2005 01:56
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
19-Oct-2004 06:22
19-Oct-2004 06:22
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.
dward at maidencreek dot com
13-Nov-2001 12:52
13-Nov-2001 12:52
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.
tbdavis at greyshirt dot net
11-Oct-2001 01:36
11-Oct-2001 01:36
Unlike the relational model, NULL in PHP has the following properties:
NULL == NULL is true,
NULL == FALSE is true.
And in line with the relational model, NULL == TRUE fails.