How does php extract the root part of a domain name?

How does php extract the root part of a domain name? & nbsp; for example, & nbsp; ww1.baidu.com & nbsp; a.www.baidu.com & nbsp; extract baidu.com ------ best solution --------- How does php extract the root part of the domain name?
How to extract the root part of a domain name, for example, ww1.baidu.com dy.baidu.com a.www.baidu.com
------ Best solution --------------------
Use the. switch array and then reverse the foreach. once a point is not a known top-level domain name or country domain name, it is what you call the root part.
------ Other solutions --------------------
$ Url = 'http: // dy.baidu.com ';
Print_r (parse_url ($ url ));

The printed array contains the data you want.