C#通过POST发送数据函数，类似asp中的xmlhttp

//purl处理页面,str参数（如：username=admin&passwod=123456）

//返回处理页面输出的内容

//使用：string data = PostData("http://www.zhangxun.net/", "action=Fav&str=这个是好网站");

       public static string PostData(string purl,string str)
        {
            try
            {
                byte[] data = System.Text.Encoding.GetEncoding("GB2312").GetBytes(str);
                // 准备请求... 
                HttpWebRequest req = (HttpWebRequest)WebRequest.Create(purl);

                //设置超时
                req.Timeout = 30000;
                req.Method = "Post";
                req.ContentType = "application/x-www-form-urlencoded";
                req.ContentLength = data.Length;
                Stream stream = req.GetRequestStream();
                // 发送数据 
                stream.Write(data, 0, data.Length);
                stream.Close();

                HttpWebResponse rep = (HttpWebResponse)req.GetResponse();
                Stream receiveStream = rep.GetResponseStream();
                Encoding encode = System.Text.Encoding.GetEncoding("GB2312");
                // Pipes the stream to a higher level stream reader with the required encoding format. 
                StreamReader readStream = new StreamReader(receiveStream, encode);

                Char[] read = new Char[256];
                int count = readStream.Read(read, 0, 256);
                StringBuilder sb = new StringBuilder("");
                while (count > 0)
                {
                    String readstr = new String(read, 0, count);
                    sb.Append(readstr);
                    count = readStream.Read(read, 0, 256);
                }

                rep.Close();
                readStream.Close();

                return sb.ToString();

            }
            catch (Exception ex)
            {
                return "";
               // ForumExceptions.Log(ex);
            }
        }