is_null($x) vs $x === null in PHP [duplicate]

Question

There is absolutely no difference in functionality between is_null and === null.

The only difference is that is_null is a function and thus

1. is marginally slower (function call overhead)
2. can be used as a callback, e.g. array_map('is_null', $array).

Personally, I use null === whenever I can, as it is more consistent with false === and true === checks.

If you want, you can check the code: is_identical_function (===) and php_is_type (is_null) do the same thing for the IS_NULL case.

---

The related isset() language construct checks whether the variable actually exists before doing the null check. So isset($undefinedVar) will not throw a notice.

Also note that isset() may sometimes return true even though the value is null - this is the case when it is used on an overloaded object, i.e. if the object defines an offsetExists/__isset method that returns true even if the offset is null (this is actually quite common, because people use array_key_exists in offsetExists/__isset).

As stated by others, there is a time difference between using === and is_null(). Did some quick testing and got these results:

<?php

//checking with ===
$a = array();
$time = microtime(true);
for($i=0;$i<10000;$i++) {
    if($a[$i] === null) {
         //do nothing
    }
}
echo 'Testing with === ', microtime(true) - $time, "\n";

//checking with is_null()
$time = microtime(true);
for($i=0;$i<10000;$i++) {
    if(is_null($a[$i])) {
         //do nothing
    }
}
echo 'Testing with is_null() ', microtime(true) - $time;
?>

Gives the results

Testing with === 0.0090668201446533

Testing with is_null() 0.013684034347534

See the code in action

They all have their places, though only isset() will avoid undefined variable warnings:

$ php -a
Interactive shell

php > var_dump(is_null($a));
PHP Notice:  Undefined variable: a in php shell code on line 1
bool(true)
php > var_dump($a === null);
PHP Notice:  Undefined variable: a in php shell code on line 1
bool(true)
php > var_dump(isset($a));
bool(false)
php >

I'm not able to say wether it's better to use is_null or === null. But be aware when using isset on arrays.

$a = array('foo' => null);

var_dump(isset($a['foo'])); // false
var_dump(is_null($a['foo'])); // true
var_dump(array_key_exists('foo', $a)); // true

You need isset() if the variable is possibly not defined. It returns false when the variable is not defined or === null (yes, it's that ugly). Only isset() and empty() do not raise an E_NOTICE if the variable or array element does not exist.

There is not really a difference between is_null and === null. I think === is much nicer but when you e.g. need to use call_user_func for some dubious reason, you'd have to use is_null.