is_null

(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

is_null Finds whether a variable is null

Description

is_null(mixed $value): bool

Finds whether the given variable is null.

Parameters

value

The variable being evaluated.

Return Values

Returns true if value 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 declared and is different than 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

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User Contributed Notes 5 notes

up
337
Malfist
16 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
166
george at fauxpanels dot com
15 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!
up
89
contact dot 01834e2c at renegade334 dot me dot uk
9 years ago
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
up
23
ahamilton9
2 years ago
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=0 ; $i<1000000000 ; $i++) {
if(
$var === null) {}
}
$after = microtime(true);
echo
' ===: ' . ($after - $before) . " seconds\n";

// Function
$before = microtime(true);
$var = null;
for (
$i=0 ; $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
up
16
ai dot unstmann at combase dot de
16 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.
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