写日志文件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace ConsoleApplication42
{   //某个项目，需要写日志到系统目录下的siyktLog，日志名称是以当天时间为文件名，写日志时，准确地写入当时时间日期，精确到毫秒
    class Program
    {
        static void Main(string[] args)
        {
           
            DateTime dt = DateTime.Now;
           
            //测试siyktLog文件夹
            string sysPath = Environment.GetFolderPath(Environment.SpecialFolder.System);
            string siyktLogPath=sysPath+"";
            if (!Directory.Exists(siyktLogPath))
            {
                Directory.CreateDirectory(siyktLogPath);
            }
            //测试当日日志文件
            string logfileName =siyktLogPath +"\\"+ dt.ToShortDateString() +".log";
            if (!File.Exists(logfileName))
            {
               FileStream tempFS = File.Create(logfileName); 
               tempFS.Close();   //要记得及时关闭，否则下面会报错
            }

            //测试文件写入
            FileStream fs = new FileStream(logfileName, FileMode.Append);
            StreamWriter sw = new StreamWriter(fs);
            string strTime=string.Format("{0:yyyy-MM-dd HH:mm:ss.ffff:}", dt);
            sw.Write(strTime);
            sw.WriteLine("第一次测试");
            sw.Close();

            Console.ReadKey();
        }
    }
}