PHP获取客户端的IP

function getClientIP(){
global $ip;
if (getenv("HTTP_CLIENT_IP"))
$ip = getenv("HTTP_CLIENT_IP");
else if(getenv("HTTP_X_FORWARDED_FOR"))//用了代理服务器时
$ip = getenv("HTTP_X_FORWARDED_FOR");
else if(getenv("REMOTE_ADDR"))
$ip = getenv("REMOTE_ADDR");
else
$ip = "Unknow";

return $ip;
}