/**
 * 获得用户的真实IP地址
 *
 * @return  string
 */
function real_ip(){
    static $realip = NULL;

    if ($realip !== NULL){
        return $realip;
    }

    if (isset($_SERVER)){
        if (isset($_SERVER[‘HTTP_X_FORWARDED_FOR‘])){
            $arr = explode(‘,‘, $_SERVER[‘HTTP_X_FORWARDED_FOR‘]);            
   /* 取X-Forwarded-For中第一个非unknown的有效IP字符串 */
            foreach ($arr AS $ip){
                $ip = trim($ip);
                if ($ip != ‘unknown‘){
                    $realip = $ip;
                    break;
                }
            }
        }elseif (isset($_SERVER[‘HTTP_CLIENT_IP‘])){
            $realip = $_SERVER[‘HTTP_CLIENT_IP‘];
        }else{
            if (isset($_SERVER[‘REMOTE_ADDR‘]))
            {
                $realip = $_SERVER[‘REMOTE_ADDR‘];
            }
            else
            {
                $realip = ‘0.0.0.0‘;
            }
        }
    }
    else
    {
        if (getenv(‘HTTP_X_FORWARDED_FOR‘))
        {
            $realip = getenv(‘HTTP_X_FORWARDED_FOR‘);
        }
        elseif (getenv(‘HTTP_CLIENT_IP‘))
        {
            $realip = getenv(‘HTTP_CLIENT_IP‘);
        }
        else
        {
            $realip = getenv(‘REMOTE_ADDR‘);
        }
    }

    preg_match("/[\d\.]{7,15}/", $realip, $onlineip);
    $realip = !empty($onlineip[0]) ? $onlineip[0] : ‘0.0.0.0‘;

    return $realip;
}