php获取客户端IP

function GetIP(){        if (getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"), "unknown"))            $ip = getenv("HTTP_CLIENT_IP");        else if (getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknown"))            $ip = getenv("HTTP_X_FORWARDED_FOR");        else if (getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unknown"))            $ip = getenv("REMOTE_ADDR");        else if (isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], "unknown"))            $ip = $_SERVER['REMOTE_ADDR'];        else            $ip = "unknown";        return($ip);    }