PHP filter_var FILTER_VALIDATE_DOMAIN expects parameter 2 to be long

Question

This simple code:

var_dump(filter_var('example.com', FILTER_VALIDATE_DOMAIN)); 
// also
var_dump(filter_var('example.com', FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME)); 

Returns:

Warning: filter_var() expects parameter 2 to be long, string given in [...]

But FILTER_VALIDATE_DOMAIN seems to be a valid filter based on this page

And that is how I understand it should be used based on filter var function.

What is wrong ?

Answer 1

It appears FILTER_VALIDATE_DOMAIN only exists in PHP 7+. It's only mentioned in the general changelog, not where you'd expect it. In older versions it's not defined, and PHP falls back to 'FILTER_VALIDATE_DOMAIN' as a bare string, and you have suppressed your error reporting and aren't seeing that notice.