PHP inet_pton returning empty string... var_dump says otherwise

Question

I am trying to save an IPv6 address in a MySQL database. I am using inet_pton to do this. However, I have noticed that some IP's (in particular this localhost IP) are returning empty strings. Example:

$ip = inet_pton('::1');

And if a do a var_dump of $ip it shows that it's length is 16, but nothing is being returned:

var_dump($ip);
// string(16) ""

What is happening here?

Answer 1

IPv6 addresses are 128bit, which is 16 bytes/chars. ::1 corresponds to 00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:01, so you're printing 15 null bytes and 0x01, which is not a printable character.