php - 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.)

Answer 1

? is true

? is false

        | isset   | is_null | ===null | ==null  | empty   |
|-------|----------|---------|---------|---------|---------|
|  null |    ?   |    ?   |    ?   |    ?  |    ?   |
|  true |    ?   |    ?   |    ?   |    ?  |    ?   |
| false |    ?   |    ?   |    ?   |    ?  |    ?   |
|     0 |    ?   |    ?   |    ?   |    ?  |    ?   |
|     1 |    ?   |    ?   |    ?   |    ?  |    ?   |
|     |    ?   |    ?   |    ?   |    ?  |    ?   |
| unset |    ?   |    ?   |    ?   |    ?  |    ?   |
|   ""  |    ?   |    ?   |    ?   |    ?  |    ?   |

Summary:??????

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

An important point is empty and isset do not trigger a PHP warning if their parameter is an undefined variable. So if you expect that the variable or array index which you are testing upon are always defined, use the operator otherwise use the function.