客户端接收到txt文件如何没有内容

        s.Format("Connected to server :- %s",servername);
    m_list.AddString(s);
    sprintf(buff,"GET %s\r\n\r\n",filepath);
    send(conn,buff,strlen(buff),0);
    s.Format("sending command :- GET %s to server",filepath);
    m_list.AddString(s);
    CFile f;
    int y;
    CString fname="c:\\";
    fname+=filename;
    f.Open(fname,CFile::modeCreate | CFile::modeWrite);
    s.Format("starting to receive file");
    m_list.AddString(s);
    while(y=recv(conn,buff,4*1024,0)>0)
    {
        f.Write(buff,y);
    }
    f.Close();