What is the difference between isset(), empty() and is_null() in PHP?

All three check a variable, but in different ways.

• isset() is true when the variable exists and is not NULL.
• empty() is true when the variable does not exist or has a false-like value (0, “”, “0”, NULL, false, []).
• is_null() is true only when the value is NULL (and it gives a warning for an undefined variable).

Value	isset()	empty()	is_null()
NULL	false	true	true
0	true	true	false
“” (empty string)	true	true	false
“Hello”	true	false	false
Undefined variable	false	true	true (with warning)

<?php
$a = null;
$b = 0;
$c = "Hello";

var_dump(isset($a), empty($a), is_null($a));
var_dump(isset($b), empty($b), is_null($b));
var_dump(isset($c), empty($c), is_null($c));
?>

Output:

Each group of three lines is for one variable: $a, $b and $c. Read the full chapters: isset(), empty() and is_null().

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