difference between is_null "== NULL" and "=== NULL" in PHP

Question

Possible Duplicate:
php == vs === operator

i have the following code fragment and it doesn't make sense to me why would NULL be evaluated in 3 different ways. Consider the variable $uploaded_filenames_array as UNKNOWN - we don't know whether it's still an array or a NULL. That's what we are trying to check.

//-----------------------------------------------
if (is_null($uploaded_filenames_array)){
    echo "is_null";
}
else{
    echo "is_NOT_null";
}
//-----------------------------------------------
if ($uploaded_filenames_array == NULL){
    echo "NULL stuff";
}
else{
    echo "not NULL stuff";
}
//-----------------------------------------------
if ($uploaded_filenames_array === NULL){
    echo "NULL identity";
}
else{
    echo "not NULL identity";
}
//-----------------------------------------------

i am getting the following response:

is_NOT_null 
NULL stuff 
not NULL identity

can somebody help to understand what is the programmatic difference between these 3 ways of checking NULL?

how is this question an exact duplicate of http://stackoverflow.com/questions/589549/php-vs-operator? That question doesn't talk about is_null. — Rakib, Aug 28 '12 at 09:54

xdazz · Accepted Answer · 2012-08-28T09:39:57.270

20

is_null($a) is same as $a === null.

($a === null is bit faster than is_null($a) for saving one function call, but it doesn't matter, just choose the style you like.)

For the difference of === and ==, read PHP type comparison tables

$a === null be true only if $a is null.

But for ==, the below also returns true.

null == false
null == 0
null == array()
null == ""

edited Aug 28 '12 at 09:39

answered Aug 28 '12 at 09:34

xdazz

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+1 for editing it out nicely with extra information :) – Fluffeh Aug 28 '12 at 09:43
-1 for editing it out nicely with extra information not relevant to the question :) – salathe Aug 28 '12 at 09:51
@salathe So what is the irrelevant part ? :) – xdazz Aug 28 '12 at 09:56
"only if"? What about unset values? http://stackoverflow.com/a/15607428/543738 – Mr. Lance E Sloan Mar 21 '16 at 15:50

score 3 · Answer 2 · edited Aug 20 '16 at 21:15

3

You should read this http://php.net/manual/en/language.operators.comparison.php. Also no need to use is_null function to check only on NULL. === is faster...

edited Aug 20 '16 at 21:15

Joaquin Marcher

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answered Aug 28 '12 at 09:32

Igor Timoshenko

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score 1 · Answer 3 · edited Aug 17 '17 at 08:44

1

== checks if the value is equal e.g.:

>> "123" == 123
<< true

=== checks if the value & type are equal e.g.:

>> "123" === 123
<< false

edited Aug 17 '17 at 08:44

Ivan

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answered Aug 28 '12 at 09:32

Genosite

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so `is_null` is identical to `===`? – Rakib Aug 28 '12 at 09:33
1

No, `is_null` checks if the value provided is not `null`, so: `function is_null($value) { return $value === null; }` – Diamondo25 Aug 28 '12 at 09:36

score 1 · Answer 4 · answered Aug 28 '12 at 09:35

The === operator tests for the same value and the same TYPE. An empty string might evaluate to null, but it is not of the null type - hence this fails.

The == operator basically checks to see if they are pretty much the same - by that, do the evaluate to the same value. Being empty, this will evaluate to null, hence this fails.

The is_null function does a fairly thorough check - much more like the === operator.

difference between is_null "== NULL" and "=== NULL" in PHP

4 Answers4

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