向Log文件中写入程序运行期间的错误信息

public static void ReportError(string errorString)
        {
            DateTime dateNow = DateTime.Now;
            string sFilePath = Application.StartupPath +"\\Log\\"+ dateNow.ToString("yyyyMM");
            string sFileName = dateNow.ToString("dd") + ".log";
            sFileName = sFilePath + "\\" + sFileName; //文件的绝对路径
            if (!Directory.Exists(sFilePath))//验证路径是否存在
            {
                Directory.CreateDirectory(sFilePath);//不存在则创建
            }
            FileStream fs;
            StreamWriter sw;
            if (File.Exists(sFileName))//验证文件是否存在，有则追加，无则创建
            {
                fs = new FileStream(sFileName, FileMode.Append, FileAccess.Write);
            }
            else
            {                
                  fs = new FileStream(sFileName, FileMode.Create, FileAccess.Write);
            }
            sw = new StreamWriter(fs);
            sw.WriteLine(dateNow.ToString("yyyy-MM-dd HH-mm-ss") + "     ---     " + errorString);
            sw.Close();
            fs.Close();

        }