How to get visitor's ip address using php (code)

if (!empty($_SERVER['HTTP_CLIENT_IP'])) {
            $ip = $_SERVER['HTTP_CLIENT_IP'];
        } elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {//检查ip是从代{过}{滤}理传递过来的
            $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
        } else {
            $ip = $_SERVER['REMOTE_ADDR'];
        }
        return $ip;

<?php
echo
"请求头IP".
"<br/>Client_IP:".getenv(&#39;HTTP_CLIENT_IP&#39;).
"<br/>X_Forwarded_For(最右为真实IP):".getenv(&#39;HTTP_X_FORWARDED_FOR&#39;).
"<br/><hr>真实IP".
"<br/>REMOTE_ADDR:".getenv(&#39;REMOTE_ADDR&#39;).
"<br/>\$_SERVER[&#39;REMOTE_ADDR&#39;]:".$_SERVER[&#39;REMOTE_ADDR&#39;];