C#保存日志文件到txt中,可追加保存，定时删除最后一次操作半年前日志文件

         /// <summary>
         /// 输出指定信息到文本文件
         /// </summary>
         /// <param name="msg">输出信息</param>
         public void WriteMessage(string msg, string userName)
         {
             try
             {

                 string mainPath = "F:\\log\\";//日志文件路径&配置到Config文件中直接获取
                 string path = mainPath;
                 string filename = DateTime.Now.ToString("yyyyMMdd") + ".txt";//文件名
                 string year = DateTime.Now.ToString("yyyy");//年
                 string month = DateTime.Now.ToString("MM");//月

                 //判断log文件路径是否存在，不存在则创建文件夹
                 if (!System.IO.Directory.Exists(path))
                 {
                     System.IO.Directory.CreateDirectory(path);//不存在就创建目录
                 }

                 path += year + "\\";
                 //判断年度文件夹是否存在，不存在则创建文件夹
                 if (!System.IO.Directory.Exists(path))
                 {
                     System.IO.Directory.CreateDirectory(path);//不存在就创建目录
                 }

                 path += month + "\\";
                 //判断月度文件夹是否存在，不存在则创建文件夹
                 if (!System.IO.Directory.Exists(path))
                 {
                     System.IO.Directory.CreateDirectory(path);//不存在就创建目录
                 }

                 //拼接完整文件路径
                 path += filename;
                 if (!File.Exists(path))
                 {
                     //文件不存在，新建文件
                     FileStream fs = new FileStream(path, FileMode.OpenOrCreate);
                     StreamWriter sw = new StreamWriter(fs);
                     sw.Close();
                 }

                 using (FileStream fs = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write))
                 {
                     using (StreamWriter sw = new StreamWriter(fs))
                     {
                         sw.BaseStream.Seek(, SeekOrigin.End);
                         //sw.WriteLine("------------------------------------------------------------------------ Info Start ");
                         sw.WriteLine("操作时间：" + DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"));
                         sw.WriteLine("操作人：" + userName);
                         sw.WriteLine("Message：{0}\n", msg, DateTime.Now);
                         sw.WriteLine("------------------------------------------------------------------------ ");
                         Console.WriteLine("\n");
                         sw.Flush();
                     }
                 }

                 //当前月份
                 int totalmonth = int.Parse(month);
                 int totalyear = int.Parse(year);
                 int tmonth = ;//保留日志时长，月度单位
                 DateTime date;
                 string datestring = "";

                 DirectoryInfo dyInfo = new DirectoryInfo(mainPath);
                 //删除历史数据，保留6个月日志
                 if (totalmonth < tmonth)
                 {
                     //删除前一年totalmonth+6月份之前的数据
                     datestring = (totalyear - ).ToString() + "-" + (totalmonth + tmonth).ToString().PadLeft(, '') + "-" + "01 00:00:00";

                 }
                 else
                 {
                     //删除当年6个月前的数据
                     datestring = (totalyear).ToString() + "-" + (totalmonth - tmonth).ToString().PadLeft(, '') + "-" + "01 00:00:00";
                 }
                 date = Convert.ToDateTime(datestring);
                 //获取文件夹下所有的文件
                 foreach (FileInfo feInfo in dyInfo.GetFiles())
                 {
                     //判断文件日期是否小于今天，是则删除
                     if (feInfo.CreationTime < date)
                         feInfo.Delete();
                 }
             }
             catch (Exception)
             {
             }
         }