PHP null var exists

Question

Possible Duplicate:
Check if value isset and null

If I have $v = NULL; how can I check that $v is exists and it's NULL?

isset($v) => false //because of NULL, but $v exists

score 5 · Accepted Answer · answered Mar 14 '12 at 19:52

5

You can’t, null is equivalent to a non-existing variable:

A variable is considered to be null if:

it has been assigned the constant NULL.

it has not been set to any value yet.

it has been unset().

Only for arrays you can check whether a key exists although its value is null using array_key_exists.

answered Mar 14 '12 at 19:52

Gumbo

+1 This answer is more correct than the others because it addresses both parts of the question ($v exists AND is null). – George Cummins Mar 14 '12 at 19:53
Erm, what's about using `array_key_exists` with `$GLOBALS`? http://www.php.net/manual/en/reserved.variables.globals.php – kirilloid Mar 14 '12 at 20:05
@kirilloid That would work – but only with [global variables](http://php.net/language.variables.scope). – Gumbo Mar 14 '12 at 21:40
I know, this is similar to JS. You cannot access global variable by its name with `window[name]`, but it's impossbile for variables in current scope. – kirilloid Mar 14 '12 at 21:44
-1 You CAN. Based on my answer [here](http://stackoverflow.com/questions/3803282/check-if-value-isset-and-null#answer-39721756), to check that $v exists and it's NULL you would do: `array_key_exists('v', compact('v')) && is_null($v);` – nzn Jan 17 '17 at 10:00

score 0 · Answer 2 · edited Mar 14 '12 at 19:51

0

Try is_null($v).

edited Mar 14 '12 at 19:51

dfsq

answered Mar 14 '12 at 19:51

2

if $v is not exists it'll return warning. – Yekver Mar 14 '12 at 19:52
@Yekver you'll need to combine both. – Alex Turpin Mar 14 '12 at 19:53
1

@Xeon06 How would you do that? As far as `isset()` and `is_null()` are concerned, the two are indistinguishable. – NullUserException Mar 14 '12 at 19:55
@Null ah you're right, I didn't think this through. – Alex Turpin Mar 15 '12 at 02:34

score 0 · Answer 3 · answered Mar 14 '12 at 19:53

0

You should be careful using isset on variables that can be null. It's a good way to set yourself up for bugs and problems in the future.

What you could do for now is to use is_null as an additional test.

answered Mar 14 '12 at 19:53

Alex Turpin

score -1 · Answer 4 · answered Mar 14 '12 at 19:52

-1

If you would like to put it all together to test existence and a null value

<?php
if(!is_null($v)){
// do something
}
?>

answered Mar 14 '12 at 19:52

Tim Wickstrom

4 Answers4