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(0, 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}
", msg, DateTime.Now);
                        sw.WriteLine("------------------------------------------------------------------------ ");
                        Console.WriteLine("
");
                        sw.Flush();
                    }
                }

                //当前月份
                int totalmonth = int.Parse(month);
                int totalyear = int.Parse(year);
                int tmonth = 6;//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 - 1).ToString() + "-" + (totalmonth + tmonth).ToString().PadLeft(2, '0') + "-" + "01 00:00:00";

                }
                else
                {
                    //删除当年6个月前的数据
                    datestring = (totalyear).ToString() + "-" + (totalmonth - tmonth).ToString().PadLeft(2, '0') + "-" + "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)
            {
            }
        }