php is null when empty? [duplicate]
I have a question regarding NULL in PHP:
$a = '';
if($a == NULL) {
echo 'is null';
}
Why do I see is null when $a is an empty string? Is that a bug?
Solution 1:
What you're looking for is:
if($variable === NULL) {...}
Note the ===.
When use ==, as you did, PHP treats NULL, false, 0, the empty string, and empty arrays as equal.
Solution 2:
As is shown in the following table, empty($foo) is equivalent to $foo==null and is_null($foo) has the same function of $foo===null. The table also shows some tricky values regarding the null comparison. (ϕ denotes an uninitialized variables. )
empty is_null
==null ===null isset array_key_exists
ϕ | T | T | F | F
null | T | T | F | T
"" | T | F | T | T
[] | T | F | T | T
0 | T | F | T | T
false | T | F | T | T
true | F | F | T | T
1 | F | F | T | T
\0 | F | F | T | T
Solution 3:
check == vs ===
'' == NULL would return true0 == NULL would return truefalse == null would return true
where as
'' === NULL would return false0 === NULL would return falsefalse === NULL would return false
Solution 4:
No it's not a bug. Have a look at the Loose comparisons with == table (second table), which shows the result of comparing each value in the first column with the values in the other columns:
TRUE FALSE 1 0 -1 "1" "0" "-1" NULL array() "php" ""
[...]
"" FALSE TRUE FALSE TRUE FALSE FALSE FALSE FALSE TRUE FALSE FALSE TRUE
There you can see that an empty string "" compared with false, 0, NULL or "" will yield true.
You might want to use is_null [docs] instead, or strict comparison (third table).
Solution 5:
This is not a bug but PHP normal behavior. It happens because the == operator in PHP doesn't check for type.
'' == null == 0 == false
If you want also to check if the values have the same type, use === instead. To study in deep this difference, please read the official documentation.