isset vs empty vs is_null

Question

I\'m trying to write a script that when a user uploads a file and does not enter a name an error is returned. I\'ve tried using is_null, empty, and isset and they all do not

Answer 1

PHP empty() vs is_null() vs isset():

            +-------+-------+-------+-------+-------+--------------+
            |  ""   | "foo" | NULL  | FALSE |   0   | undefined    |
+-----------+-------+-------+-------+-------+-------+--------------+
| empty()   | TRUE  | FALSE | TRUE  | TRUE  | TRUE  | TRUE         |
| is_null() | FALSE | FALSE | TRUE  | FALSE | FALSE | TRUE (ERROR) |
| isset()   | TRUE  | TRUE  | FALSE | TRUE  | TRUE  | FALSE        |
+-----------+-------+-------+-------+-------+-------+--------------+

If you want to check if there's any value other than null or undefined, use isset($var)
(because !is_null() generates a warning on undefined variables.)

If you want to check if the value is non-blank text or any number including zero, it gets trickier:

if (!empty($v) || (isset($v) && ($v === 0 || $v === '0'))) {
    // $v is non-blank text, true, 0 or '0'
    // $v is NOT an empty string, null, false or undefined
}