c#写LOG文件

           DateTime dt = DateTime.Now;
            string filename = dt.ToString("yyyy-MM-dd") + "_log.txt";
            string path =System.AppDomain.CurrentDomain.BaseDirectory+ "log\\";
            System.Diagnostics.Trace.WriteLine(path);
            FileStream fs;
            if (!File.Exists(path + filename))
            {
                fs = new FileStream(path + filename, FileMode.Create, FileAccess.Write);
            }
            else {
                fs = new FileStream(path + filename, FileMode.Open, FileAccess.Write);
            }
            //追加写入
            StreamWriter sw = new StreamWriter(fs);
            long fl = fs.Length;
            fs.Seek(fl, SeekOrigin.Begin);
            sw.WriteLine(DateTime.Now.ToString() + "\n_S:________ \n" + msg + "\n __________End.\n");//开始写入值
            //结束
            sw.Close();
            fs.Close();