Why does gettype() output "NULL" for an undefined variable?

Question

I have tried the following code:

<?php
    echo gettype($x);
?>

And I got the following output:

Why did gettype() outputted "NULL" after the error was displayed? I mean an undefined variable is a variable that doesn't exist and not a NULL variable, right?

Answer 1

The documentation of NULL explains:

The special NULL value represents a variable with no value. NULL is the only possible value of type null.

A variable is considered to be null if:

• it has been assigned the constant NULL.
• it has not been set to any value yet.
• it has been unset().

Also check the table "Comparisons of $x with PHP functions".