What's the difference between is_null($var) and ($var === null)?

Question

Is there any difference between this...

if (is_null($var)) {
    do_something();
}

and this?

if ($var === null) {
    do_something();
}

Which form is better when checking whether or not a variable contains null? Are there any edge cases I should be aware of? (I initialize all my variables, so nonexistent variables are not a problem.)

You would think the `===` operator would be faster since it's not an explicit function... but I've been surprised once or twice. — John Giotta, Jan 11 '11 at 21:01

Handsome Nerd · Answer 1 · 2022-12-06T23:35:59.503

124

empty() and isset() do not trigger a PHP warning if their parameter is an undefined variable. In most cases, such a warning is desirable to pinpoint the bugs. So only use the functions if you believe your variable can be legitimately undefined. It normally happens with an array index.

✅ is true

❌ is false

        |  isset   | is_null | === null | == null | empty   |
|-------|----------|---------|----------|---------|---------|
| unset |    ❌   |    ✅   |    ✅    |    ✅  |    ✅   |
|  null |    ❌   |    ✅   |    ✅    |    ✅  |    ✅   |
|  true |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
| false |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|     0 |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|     1 |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
|    \0 |    ✅   |    ❌   |    ❌    |    ❌  |    ❌   |
|    "" |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |
|    [] |    ✅   |    ❌   |    ❌    |    ✅  |    ✅   |

Summary:♦️

empty is equivalent to == null
is_null is equivalent to === null
isset is inverse of is_null and === null

edited Dec 06 '22 at 23:35

answered Mar 25 '13 at 04:02

Handsome Nerd

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I really love this table. – Cheok Yan Cheng Feb 19 '14 at 08:58
3

it might make the table slightly more clear to have the first column named `$v` to represent some generic variable, and then the others `isset($v)`, `is_null($v)`, `$v===null` and so on – Brandin Oct 19 '14 at 18:30
@Brandin Thanks for the suggestion. Feel free to edit the answer. – Handsome Nerd Oct 20 '14 at 05:35
@PHPst, Actually this **doesn't answer the question asked**: What's the difference between `is_null` vs `=== null`. – Pacerier Mar 08 '15 at 22:18
1

`isset` will not complain about an undefined variable, it will return false. Using `is_null` or `=== null` will result in a notice. – user1431317 Jun 08 '16 at 10:25
1

The misaligned columns in this table are causing me a lot of stress. – hackel Oct 25 '20 at 00:03

score 36 · Accepted Answer · edited Feb 28 '13 at 08:20

36

Provided the variable is initialized (which you did indicate - though I'm not 100% sure if this matters in this context or not. Both solutions might throw a warning if the variable wasn't defined), they are functionally the same. I presume === would be marginally faster though as it removes the overhead of a function call.

It really depends on how you look at your condition.

=== is for a strict data comparison. NULL has only one 'value', so this works for comparing against NULL (which is a PHP constant of the null 'value')

is_null is checking that the variable is of the NULL data type.

It's up to you which you choose, really.

edited Feb 28 '13 at 08:20

alex

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answered Jan 11 '11 at 21:01

Craige

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Thanks for explaining compare-by-value vs. compare-by-type. – kijin Jan 11 '11 at 21:21
7

I prefer the `is_null` variant, because it is easy to accidentally use `== null` instead of `=== null`. Since `== null` is the same as `empty` (see other answer), this introduces greater potential for programmer (especially junior and mid-level) error than a simple and readable `is_null`. – ryanm Mar 29 '17 at 15:11

score 19 · Answer 3 · answered Jan 11 '11 at 21:00

19

Both are exactly same, I use is_null because it makes my code more readable

answered Jan 11 '11 at 21:00

Ish

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and while === may be faster at first, PHP optimiser should remedy that. – foo Jan 11 '11 at 21:22
13

I feel `is_null` is actually less clear. While it may read nicely, `$v === null` leaves no doubt that the comparison is done with strict semantics, but with `is_null($v)`, some coders will wonder if it uses `===` or `==` semantics. – goat Sep 28 '14 at 16:08
5

@goat, ish1301, Also, `is_null` could be [removed or redefined](http://php.net/manual/en/function.runkit-function-remove.php) entirely, whereas `=== null` will always work. – Pacerier Mar 09 '15 at 03:15
@Pacerier while your example is interesting the likelihood of someone installing the runkit pecl package, then setting it up to allow removing built in functions and then removing is_null, of all things, without replacing it with something is very close to nil, or null if you prefer. The only scenario I can think of where a person would want to remove is_null, is if they wanted to change the behavior of the null comparison globally. For example; returning false instead of true for unset; In this case it would actually only be possible if the code was written with is_null to begin with. – kaan_a Jan 16 '20 at 11:49
They are not exactly the same, one is a function with call back option, the other is a straight comparison on a value – James Oct 22 '21 at 15:17

goat · Answer 4 · 2012-03-06T14:52:50.703

7

If it seems redundant for php to have so many is_foo() type functions, when you can just use a standard comparison operators, consider programatically called functions.

$arrayOfNullValues = array_filter($myArray, 'is_null');

edited Mar 06 '12 at 14:52

answered Jan 11 '11 at 21:30

goat

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`$arrayWithoutNullValues` would store an array that has *only* `null` values, then. – PointedEars Feb 28 '12 at 16:00

lonesomeday · Answer 5 · 2011-01-11T21:18:11.997

6

I've just run a quick benchmark, testing a million iterations of each. is_null took 8 seconds to complete; === null took 1.

So a call to is_null is 0.000007s slower than a call to === on my computer.

I'd find something more useful to optimise.

My code:

<?php

$start = time();
$var = null;

for ($i = 1000000; $i--; ) {
    is_null($var);
}

echo time() - $start;

$start = time();

for ($i = 1000000; $i--; ) {
    $var === null;
}

echo time() - $start;

edited Jan 11 '11 at 21:18

answered Jan 11 '11 at 21:09

lonesomeday

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Interestingly, PHP/7 seems to have addressed this and performance is now almost identical; in fact, `is_null()` is slightly faster in my computer under 7.1.9 Win32. – Álvaro González Oct 20 '17 at 08:31
@ÁlvaroGonzález I noticed the same thing. The difference is negligible between the two functions. (is_null: 0.54486592610677, === null: 0.7440135592506) at 10,000 operations. The test was ran 30 times, and these numbers are the average. – Justin E Dec 05 '17 at 23:50

score 2 · Answer 6 · answered Jan 11 '11 at 21:01

2

I would use the built in PHP function over the operator comparison every time.

answered Jan 11 '11 at 21:01

Michael Irigoyen

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Care to update your answer to cite some logical or technical reasons? As it stands it's simply an opinion – James Oct 22 '21 at 15:14

score 1 · Answer 7 · answered Sep 19 '19 at 07:13

1

One thing people often forget to mention in this discussion is that if you are all about strict type checking, is_null will help you to never make a typo in your comparison operators (== vs ===).

answered Sep 19 '19 at 07:13

Ogier Schelvis

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score 0 · Answer 8 · answered Jan 11 '11 at 21:09

0

is_null($var) is about 14 times slower than $var===null... 37.8 ms vs. 2.6 ms.

But actually I don't know why.

answered Jan 11 '11 at 21:09

Floern

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Because it's a function and it has overhead (e.g. setting up the callback etc). However in PHP7 it's about the same (reports show the function is actually marginally faster) – James Oct 22 '21 at 15:16

What's the difference between is_null($var) and ($var === null)?

8 Answers8

Summary:♦️

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