c#基础篇

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1.readonly 和const常量

（1）const只能在字段的声明语句中初始化，而readonly可以在声明语句和构造函数中都可以，readonly 字段被赋值了就不能改变

（2）readonly可以是实例字段也可以是静态字段

（3）readonly分配内存，const不分配

（4）const的值是在编译期决定的，readonly则是在运行期

获取公网ip

/// <summary>
        /// 获取本机的上网IP
        /// </summary>
        /// <returns></returns>
        private string GetConnectNetAddress()
        {
            string strUrl = "

http://www.ip138.com/ip2city.asp"; //获得IP的网址
            Uri uri = new Uri(strUrl);
            WebRequest webreq = WebRequest.Create(uri);
            Stream s = webreq.GetResponse().GetResponseStream();
            StreamReader sr = new StreamReader(s, Encoding.Default);
            string all = sr.ReadToEnd(); //读取网站返回的数据格式：您的IP地址是：[x.x.x.x]
            int i = all.IndexOf("[") + 1;
            string tempip = all.Substring(i, 15);
            string ip = tempip.Replace("]", "").Replace(" ", "").Replace("<", "");
            return ip;
        }

/// <summary>
    /// 获取用户远程ip
    /// </summary>
    /// <returns></returns>
    private string GetUserHostIp()
    {
        string ip = string.Empty;
        if (HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"] != null)
        {
            ip = HttpContext.Current.Request.ServerVariables["HTTP_X_FORWARDED_FOR"];
        }
        else if ((string.IsNullOrEmpty(ip) || ip.Length <= 0) && HttpContext.Current.Request.ServerVariables["Proxy-Client-IP"] != null)
        {
            ip = HttpContext.Current.Request.ServerVariables["Proxy-Client-IP"];
        }
        else if ((string.IsNullOrEmpty(ip) || ip.Length <= 0) && HttpContext.Current.Request.ServerVariables["WL-Proxy-Client-IP"] != null)
        {
            ip = HttpContext.Current.Request.ServerVariables["WL-Proxy-Client-IP"];
        }
        else if ((string.IsNullOrEmpty(ip) || ip.Length <= 0) && HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"] != null)
        {
            ip = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
        }
        else if (string.IsNullOrEmpty(ip) || ip.Length <= 0)
        {
            ip = HttpContext.Current.Request.UserHostAddress;
        }
        return ip;
    }

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