is_null

(PHP 4 >= 4.0.4, PHP 5)

is_null Finds whether a variable is NULL

Description

bool is_null ( mixed $var )

Finds whether the given variable is NULL.

Parameters

var

The variable being evaluated.

Return Values

Returns TRUE if var is null, FALSE otherwise.

Examples

Example #1 is_null() example

<?php

error_reporting
(E_ALL);

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

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

See Also

  • The NULL type
  • isset() - Determine if a variable is set and is not NULL
  • is_bool() - Finds out whether a variable is a boolean
  • is_numeric() - Finds whether a variable is a number or a numeric string
  • is_float() - Finds whether the type of a variable is float
  • is_int() - Find whether the type of a variable is integer
  • is_string() - Find whether the type of a variable is string
  • is_object() - Finds whether a variable is an object
  • is_array() - Finds whether a variable is an array

Коментарии

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(nulltruefalse01''"\0""unset");

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

    echo 
is_null($var) ? 0;
    echo isset(
$var) ? 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.
2008-01-14 14:17:03
http://php5.kiev.ua/manual/ru/function.is-null.html
Автор:
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.
2008-07-01 10:54:06
http://php5.kiev.ua/manual/ru/function.is-null.html
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!
2008-12-01 15:58:13
http://php5.kiev.ua/manual/ru/function.is-null.html
In PHP 7 (phpng), is_null is actually marginally faster than ===, although the performance difference between the two is far smaller.

PHP 5.5.9
is_null - float(2.2381200790405)
===     - float(1.0024659633636)
=== faster by ~100ns per call

PHP 7.0.0-dev (built: May 19 2015 10:16:06)
is_null - float(1.4121870994568)
===     - float(1.4577329158783)
is_null faster by ~5ns per call
2015-05-25 09:57:13
http://php5.kiev.ua/manual/ru/function.is-null.html
Автор:
A quick test in 2022 on PHP 8.1 confirms there is still no need to micro-optimize NULL checks:

<?php

// Comparison Operator
$before microtime(true);
$var null;
for (
$i=$i<1000000000 $i++) {
    if(
$var === null) {}
}
$after microtime(true);
echo 
'    ===: ' . ($after $before) . " seconds\n";

// Function
$before microtime(true);
$var null;
for (
$i=$i<1000000000 $i++) {
    if(
is_null($var)) {}
}
$after microtime(true);
echo 
'is_null: ' . ($after $before) . " seconds\n";

//     ===: 4.1487579345703 seconds
// is_null: 4.1316878795624 seconds
2022-04-19 23:28:04
http://php5.kiev.ua/manual/ru/function.is-null.html

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