c# 用System.Net 读取网页源代码

 System.Net.HttpWebRequest req;
System.Net.HttpWebResponse res;
            string url="http://www.baidu.com";
           req = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(url);
           res = (System.Net.HttpWebResponse)req.GetResponse();
           System.IO.StreamReader strm = new System.IO.StreamReader(res.GetResponseStream(), Encoding.GetEncoding("gb2312"));
            MessageBox.Show(strm.ReadToEnd());