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is_null

(PHP 4 >= 4.0.4, PHP 5)

is_null Prüft ob eine Variable NULL enthält

Beschreibung

bool is_null ( mixed $var )

Prüft ob die gegebene Variable NULL enthält

Parameter-Liste

var

Die zu prüfende Variable.

Rückgabewerte

Liefert TRUE wenn var null enthält, sonst FALSE.

Beispiele

Beispiel #1 is_null()-Beispiel

<?php

error_reporting
(E_ALL);

$foo NULL;
var_dump(is_null($inexistent), is_null($foo));

?>
Notice: Undefined variable: inexistent in ...
bool(true)
bool(true)

Siehe auch

  • Der NULL-Typ
  • isset() - Prüft, ob eine Variable existiert und ob sie nicht NULL ist
  • is_bool() - Prüft, ob eine Variable vom Typ boolean ist
  • is_numeric() - Prüft, ob eine Variable eine Zahl oder ein numerischer String ist
  • is_float() - Prüft, ob eine Variable vom Typ float ist
  • is_int() - Prüft, ob eine Variable vom Typ int ist
  • is_string() - Prüft, ob Variable vom Typ string ist
  • is_object() - Prüft, ob eine Variable vom Typ object ist
  • is_array() - Prüft, ob die Variable ein Array ist

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User Contributed Notes 8 notes

up
57
Malfist
6 years ago
Micro optimization isn't worth it.

You had to do it ten million times to notice a difference, a little more than 2 seconds

$a===NULL; Took: 1.2424390316s
is_null($a); Took: 3.70693397522s

difference = 2.46449494362
difference/10,000,000 = 0.000000246449494362

The execution time difference between ===NULL and is_null is less than 250 nanoseconds. Go optimize something that matters.
up
24
george at fauxpanels dot com
5 years ago
See how php parses different values. $var is the variable.

$var        =    NULL    ""    0    "0"    1

strlen($var)    =    0    0    1    1    1
is_null($var)    =    TRUE    FALSE    FALSE    FALSE    FALSE
$var == ""    =    TRUE    TRUE    TRUE    FALSE    FALSE
!$var        =    TRUE    TRUE    TRUE    TRUE    FALSE
!is_null($var)    =    FALSE    TRUE    TRUE    TRUE    TRUE
$var != ""    =    FALSE    FALSE    FALSE    TRUE    TRUE
$var        =    FALSE    FALSE    FALSE    FALSE    TRUE

Peace!
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22
strrev xc.noxeh@ellij
6 years ago
$var===NULL is much faster than is_null($var) (with the same result)

I did some benchmarking with 10 million iterations:

$a=null;
isset($a); Took: 1.71841216087s
$a==NULL; Took: 1.27205181122s
$a===NULL; Took: 1.2424390316s
is_null($a); Took: 3.70693397522s
$a=5;
isset($a); Took: 1.15165400505s
$a==NULL; Took: 1.41901302338s
$a===NULL; Took: 1.21655392647s
is_null($a); Took: 3.78501200676s
error_reporting(E_ALL&~E_NOTICE);
unset($a);
isset($a); Took: 1.51441502571s
$a==NULL; Took: 16.5414860249s
$a===NULL; Took: 16.1273870468s
is_null($a); Took: 23.1918480396s

Please note, that isset is only included because it gives a good performance in any case; HOWEVER isset is NOT the same, or the opposite.
But you might be able to use isset() instead of null-checking.

You should not use is_null, except when you need a callback-function, or for conformity with is_int, is_float, etc.
up
4
normadize (a) gmail (d) com
2 years ago
Using === NULL instead of is_null(), is actually useful in loaded server scenarios where you have hundreds or thousands of requests per second. Saving microseconds on a lot of "simple" operations in the entire PHP execution chain usually results in being able to serve more pages per second at the same speed, or lowering your cpu usage. People usually write very bad and slow code.
up
2
ai dot unstmann at combase dot de
6 years ago
For what I realized is that  is_null($var)  returns exactly the opposite of  isset($var) , except that is_null($var) throws a notice if $var hasn't been set yet.

the following will prove that:

<?php

$quirks
= array(null, true, false, 0, 1, '', "\0", "unset");

foreach(
$quirks as $var) {
    if (
$var === "unset") unset($var);

    echo
is_null($var) ? 1 : 0;
    echo isset(
$var) ? 1 : 0;
    echo
"\n";
}

?>

this will print out something like:

10    // null
01    // true
01    // false
01    // 0
01    // 1
01    // ''
01    // "\0"
Notice:  Undefined variable: var in /srv/www/htdocs/sandbox/null/nulltest.php on line 8
10    // (unset)

For the major quirky types/values is_null($var) obviously always returns the opposite of isset($var), and the notice clearly points out the faulty line with the is_null() statement. You might want to examine the return value of those functions in detail, but since both are specified to return boolean types there should be no doubt.

A second look into the PHP specs tells that is_null() checks whether a value is null or not. So, you may pass any VALUE to it, eg. the result of a function.
isset() on the other hand is supposed to check for a VARIABLE's existence, which makes it a language construct rather than a function. Its sole porpuse lies in that checking. Passing anything else will result in an error.

Knowing that, allows us to draw the following unlikely conclusion:

isset() as a language construct is way faster, more reliable and powerful than is_null() and should be prefered over is_null(), except for when you're directly passing a function's result, which is considered bad programming practice anyways.
up
0
powderz at gmail dot com
8 years ago
Actually, since a wrapper is going to be written, you can check for your own version null values...if you want to be creative for some reason.

<?php
function isnull($data)
{
 
/** only if you need this
  if (is_string($data)) {
    $data = strtolower($data);
  }
  */
 
switch ($data) {
   
// Add whatever your definition of null is
    // This is just an example
    //-----------------------------
   
case 'unknown': // continue
   
case 'undefined': // continue
    //-----------------------------
   
case 'null': // continue
   
case 'NULL': // continue
   
case NULL:
      return
true;
  }
 
// return false by default
 
return false;
}
?>
up
-2
michael at cannonbose dot com
10 years ago
Regarding avoidance of NULLs in your MySQL queries, why not use  IS NULL and IS NOT NULL in your WHERE clauses.

SELECT *
FROM someDatabase
WHERE someAttribute IS NOT NULL

Cheers,

Michael
up
-8
uioreanu at hotmail dot com
13 years ago
Don't try to test
if ($intSomething==NULL) {
...
}
use is_null() instead.
The first statement misses 0 values.

Regards,
Calin

[Ed. note: this is because == tests for equivalence of value, but not type. NULL evaluates to
false, as does 0, so NULL == 0 is true--even though 0 is type int and NULL is type null.
You should use either is_null() as noted or ===, which returns true only if its operands are
equal and of the same type.]
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