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(PHP 4 >= 4.0.4, PHP 5)
is_null — Prüft ob eine Variable NULL enthält
Die zu prüfende Variable.
Liefert TRUE wenn var null enthält, sonst FALSE.
Beispiel #1 is_null()-Beispiel
<?php
error_reporting(E_ALL);
$foo = NULL;
var_dump(is_null($inexistent), is_null($foo));
?>
Notice: Undefined variable: inexistent in ... bool(true) bool(true)
A small but important difference between "is_null" and "isset" is the following: "is_null" tests if an *expression* (not a *variable*) is null, while "isset" tests if a *variable* has null value or is undefined. The difference is manifested in the two following experiments:
Experiment 1:
<?php
function test() { return null; }
var_dump(is_null(test())); // displays "true"
var_dump(isset(test())); // parse error, because "test()" is not a variable
?>
Experiment 2:
<?php
error_reporting(E_ALL);
var_dump(isset($an_undefined_variable)); // displays "false" since "$an_undefined_variable" is not defined
var_dump(is_null($an_undefined_variable)); // displays "true" (as expected), but throws a notice because "$an_undefined_variable" is not defined.
?>
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!
Testing for a NULL field/column returned by a mySQL query.
Say you want to check if field/column “foo” from a given row of the table “bar” when returned by a mySQL query is null.
You just use the “is_null()” function:
[connect…]
$qResult=mysql_query("Select foo from bar;");
while ($qValues=mysql_fetch_assoc($qResult))
if (is_null($qValues["foo"]))
echo "No foo data!";
else
echo "Foo data=".$qValues["foo"];
[…]
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.
$var===NULL is much faster than is_null($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.
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($var), and the notice clearly points out the faulty line with the is_null() statement. You might want to examine the return value of those functions in detail, but since both are specified to return boolean types there should be no doubt.
A second look into the PHP specs tells that is_null() checks whether a value is null or not. So, you may pass any VALUE to it, eg. the result of a function.
isset() on the other hand is supposed to check for a VARIABLE's existence, which makes it a language construct rather than a function. Its sole porpuse lies in that checking. Passing anything else will result in an error.
Knowing that, allows us to draw the following unlikely conclusion:
isset() as a language construct is way faster, more reliable and powerful than is_null() and should be prefered over is_null(), except for when you're directly passing a function's result, which is considered bad programming practice anyways.
Actually, since a wrapper is going to be written, you can check for your own version null values...if you want to be creative for some reason.
<?php
function isnull($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;
}
?>
I've tested different values in order to compare 'em with NULL with the help of different operators...
<?php
$arr=array(0, 0.0, '0', '0.0', '',FALSE,'false',NULL, 'NULL');
for ($i=0; $i<count($arr); $i++)
$arr[$i]=array(
$arr[$i],
((integer)($arr[$i]==NULL))
.((integer)($arr[$i]===NULL))
.((integer)is_null($arr[$i]))
);
var_dump($arr);
?>
it gave the following results:
0 : ==NULL
0.0 : ==NULL
'0' : nothing worked =)
'0.0' : nothing...
'' : ==NULL
FALSE : ==NULL
'false' : nothing
NULL : ==NULL, ===NULL, is_null()
'NULL' : nothing
enjoy =)
Regarding avoidance of NULLs in your MySQL queries, why not use IS NULL and IS NOT NULL in your WHERE clauses.
SELECT *
FROM someDatabase
WHERE someAttribute IS NOT NULL
Cheers,
Michael
Don't try to test
if ($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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