Question

WIll there be any reason why if ($str == "") and if (empty($str)) don’t produce the same output?

Answer 1

$str == "" will return TRUE for

• $str = "";
• $str = false;
• $str = NULL;
• $str = 0;
• $str = 0.0;

$str == "" will return FALSE for

• $str = "0";
• $str = array();

Note: It will also return TRUE for an undefined variable but it is a warning.

On the other hand empty($str) will be TRUE for all the cases above (including the undefined variable), with no warning.

As for the reason of this difference, it is because the function empty is intended to test for an emtpy variable (of any type, for example an array or a number*) not only an empty string.

*: as you may now PHP is happy with numbers stored in strings, it will just convert the value as needed, for example echo "1" + 2 gives 3. And that’s why empty($str) returns TRUE when $str = "0", not because of it being an empty string (it’s not) but because it is an empty number.

For testing if an string is empty, I strongly recomend to use either $str === '' or strlen($str) === 0.