php获取ip

public static function  getIP()
{
    if (getenv("HTTP_CLIENT_IP"))

        $ip = getenv("HTTP_CLIENT_IP");

    else if (getenv("HTTP_X_FORWARDED_FOR"))

        $ip = getenv("HTTP_X_FORWARDED_FOR");

    else if (getenv("REMOTE_ADDR"))

        $ip = getenv("REMOTE_ADDR");

    else $ip = "Unknow";

    return $ip;
}