用文字檔寫LOG

string _file = @"c:\" + System.DateTime.Now.ToString("yyyyMMddHHmmssfff") + ".txt";
        System.IO.FileStream fileStream = new System.IO.FileStream(_file, System.IO.FileMode.Create);
        fileStream.Close();
        using (System.IO.StreamWriter sw = new System.IO.StreamWriter(_file))
        {
            sw.Write(str);
        }