C#中怎样把流文件转换为字符串

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
request.Method = "GET";
Stream receiveStream = response.GetResponseStream();
StreamReader readStream = new StreamReader(receiveStream, Encoding.UTF8);
string SourceCode = readStream.ReadToEnd();
response.Close();
readStream.Close();

SourceCode 就是那个字符串

System.IO.StreamReader sr = new System.IO.StreamReader(s);
string str=sr.ReadToEnd();//字符串

StreamReader reader = new StreamReader(stream, Encoding.UTF8);
string aaa = reader.ReadToEnd();