获取用户真实IP,php实现

function get_client_ip() {
   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);
}