PHP取得客户端IP地址代码

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"); 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);
}