PHP: Hypertext Preprocessor (original) (raw)

is_null

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

is_null — Finds whether a variable is [null](reserved.constants.php#constant.null)

Description

Parameters

value

The variable being evaluated.

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)

Found A Problem?

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.

george at fauxpanels dot com ¶

16 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!

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

ahamilton9 ¶

3 years ago

`A quick test in 2022 on PHP 8.1 confirms there is still no need to micro-optimize NULL checks:

i<1000000000;i<1000000000 ; 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<1000000000 ; i<1000000000;i++) { if(is_null($var)) {} } $after = microtime(true); echo 'is_null: ' . ($after - $before) . " seconds\n";// ===: 4.1487579345703 seconds // is_null: 4.1316878795624 seconds ` [ **_ai dot unstmann at combase dot de_**](#80409)[ ¶](#80409) **17 years ago** `For what I realized is that is_null($var) returns exactly the opposite of isset($var) , except that is_null($var) throws a notice if $var hasn't been set yet. the following will prove that: quirksasquirks as quirksasvar) { if ($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: