php 获取ip地址

<?php
function GetIP(){
if(!empty($_SERVER["HTTP_CLIENT_IP"])){
  $cip = $_SERVER["HTTP_CLIENT_IP"];
}
elseif(!empty($_SERVER["HTTP_X_FORWARDED_FOR"])){
  $cip = $_SERVER["HTTP_X_FORWARDED_FOR"];
}
elseif(!empty($_SERVER["REMOTE_ADDR"])){
  $cip = $_SERVER["REMOTE_ADDR"];
}
else{
  $cip = "无法获取！";
}
return $cip;
}
echo GetIP();
?>