C#winform-post请求
各位大侠，我现在是想向http://dwz.cn/create.php,发送POST请求，发送的内容是：www.baidu.com

但是返回一直是错误的，请指点。
string postDataStr = "www.baidu.com";
  string Url = "http://dwz.cn/create.php";
  HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
  request.CookieContainer = new CookieContainer();
  request.Method = "POST";
  request.ContentLength = postDataStr.Length;
  Stream myRequestStream = request.GetRequestStream();
  StreamWriter myStreamWriter = new StreamWriter(myRequestStream, Encoding.GetEncoding("gb2312"));
  myStreamWriter.Write(postDataStr);
  myStreamWriter.Close();
   
  HttpWebResponse response = (HttpWebResponse)request.GetResponse();
  Stream myResponseStream = response.GetResponseStream();
  StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
  string retString = myStreamReader.ReadToEnd();
  MessageBox.Show(retString.ToString());

请求：向dwz.cn/create.php发送post请求，发送数据包括url=www.baidu.com
status!=0 出错，查看err_msg获得错误信息（UTF-8编码） 
成功，返回生成的短网址 tinyurl字段 


请指点下为何我返回的信息是错误呢，请高手指点。


------解决方案--------------------
request.ContentType="application/x-www-form-urlencoded";
------解决方案--------------------
你提交的格式不正确，没有longurl
------解决方案--------------------
你在浏览器里面的测试url是什么？表单名称完全一样才可以
------解决方案--------------------
string postDataStr = "url=www.baidu.com&alias=&access_type=web";
返回
{"longurl":"www.baidu.com","status":0,"tinyurl":"http:\/\/dwz.cn\/yes"}表示成功