how to get IP address of visitor using php

In this web programming tutorial we will learn that how we can get or track real (orignal) IP address of visitor of our page.

return !empty($_SERVER['HTTP_CLIENT_IP']) ?
$_SERVER['HTTP_CLIENT_IP'] : (!empty($_SERVER['HTTP_X_FORWARDED_FOR']) ?
$_SERVER['HTTP_X_FORWARDED_FOR'] : (!empty($_SERVER['REMOTE_ADDR']) ?
$_SERVER['REMOTE_ADDR'] : null));