C# 调用windows时间同步服务获取准确时间

//创建一个Daytime类代码如下：
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Runtime.InteropServices;  

public class Daytime
{
    // Internet Time Server class by Alastair Dallas 01/27/04  

    // Number of seconds
    private const int THRESHOLD_SECONDS = ;
    // that Windows clock can deviate from NIST and still be okay  

    //Server IP addresses from
    //http://www.boulder.nist.gov/timefreq/service/time-servers.html
    private static string[] Servers = {
        "129.6.15.28",
        "129.6.15.29",
        "132.163.4.101",
        "132.163.4.102",
        "132.163.4.103",
        "128.138.140.44",
        "192.43.244.18",
        "131.107.1.10",
        "66.243.43.21",
        "216.200.93.8",
        "208.184.49.9",
        "207.126.98.204",
        "205.188.185.33"
//65.55.21.15time.windows.com微软时间同步服务器
    };
    public static string LastHost = "";  

    public static DateTime LastSysTime;
    public static DateTime GetTime()
    {
        //Returns UTC/GMT using an NIST server if possible,
        // degrading to simply returning the system clock  

        //If we are successful in getting NIST time, then
        // LastHost indicates which server was used and
        // LastSysTime contains the system time of the call
        // If LastSysTime is not within 15 seconds of NIST time,
        //  the system clock may need to be reset
        // If LastHost is "", time is equal to system clock  

        string host = null;
        DateTime result = default(DateTime);  

        LastHost = "";
        foreach (string host_loopVariable in Servers)
        {
            host = host_loopVariable;
            result = GetNISTTime(host);
            if (result > DateTime.MinValue)
            {
                LastHost = host;
                break; // TODO: might not be correct. Was : Exit For
            }
        }  

        if (string.IsNullOrEmpty(LastHost))
        {
            //No server in list was successful so use system time
            result = DateTime.UtcNow;
        }  

        return result;
    }  

    public static int SecondsDifference(DateTime dt1, DateTime dt2)
    {
        TimeSpan span = dt1.Subtract(dt2);
        return span.Seconds + (span.Minutes * ) + (span.Hours * );
    }  

    public static bool WindowsClockIncorrect()
    {
        DateTime nist = GetTime();
        if ((Math.Abs(SecondsDifference(nist, LastSysTime)) > THRESHOLD_SECONDS))
        {
            return true;
        }
        return false;
    }  

    private static DateTime GetNISTTime(string host)
    {
        //Returns DateTime.MinValue if host unreachable or does not produce time
        DateTime result = default(DateTime);
        string timeStr = null;  

        try
        {
            StreamReader reader = new StreamReader(new TcpClient(host, ).GetStream());
            LastSysTime = DateTime.UtcNow;
            timeStr = reader.ReadToEnd();
            reader.Close();
        }
        catch (SocketException ex)
        {
            //Couldn't connect to server, transmission error
            Debug.WriteLine("Socket Exception [" + host + "]");
            return DateTime.MinValue;
        }
        catch (Exception ex)
        {
            //Some other error, such as Stream under/overflow
            return DateTime.MinValue;
        }  

        //Parse timeStr
        if ((timeStr.Substring(, ) != "UTC(NIST)"))
        {
            //This signature should be there
            return DateTime.MinValue;
        }
        if ((timeStr.Substring(, ) != ""))
        {
            //Server reports non-optimum status, time off by as much as 5 seconds
            return DateTime.MinValue;
            //Try a different server
        }  

        int jd = int.Parse(timeStr.Substring(, ));
        int yr = int.Parse(timeStr.Substring(, ));
        int mo = int.Parse(timeStr.Substring(, ));
        int dy = int.Parse(timeStr.Substring(, ));
        int hr = int.Parse(timeStr.Substring(, ));
        int mm = int.Parse(timeStr.Substring(, ));
        int sc = int.Parse(timeStr.Substring(, ));  

        if ((jd < ))
        {
            //Date is before 1900
            return DateTime.MinValue;
        }
        if ((jd > ))
            yr += ;
        else
            yr += ;  

        return new DateTime(yr, mo, dy, hr, mm, sc);
    }  

    [StructLayout(LayoutKind.Sequential)]
    public struct SYSTEMTIME
    {
        public Int16 wYear;
        public Int16 wMonth;
        public Int16 wDayOfWeek;
        public Int16 wDay;
        public Int16 wHour;
        public Int16 wMinute;
        public Int16 wSecond;
        public Int16 wMilliseconds;
    }
    [DllImport("kernel32.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true)]
    private static extern Int32 GetSystemTime(ref SYSTEMTIME stru);
    [DllImport("kernel32.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true)]
    private static extern Int32 SetSystemTime(ref SYSTEMTIME stru);  

    public static void SetWindowsClock(DateTime dt)
    {
        //Sets system time. Note: Use UTC time; Windows will apply time zone  

        SYSTEMTIME timeStru = default(SYSTEMTIME);
        Int32 result = default(Int32);  

        timeStru.wYear = (Int16)dt.Year;
        timeStru.wMonth = (Int16)dt.Month;
        timeStru.wDay = (Int16)dt.Day;
        timeStru.wDayOfWeek = (Int16)dt.DayOfWeek;
        timeStru.wHour = (Int16)dt.Hour;
        timeStru.wMinute = (Int16)dt.Minute;
        timeStru.wSecond = (Int16)dt.Second;
        timeStru.wMilliseconds = (Int16)dt.Millisecond;
        result = SetSystemTime(ref timeStru);
    }
}  

调用方法：
Daytime.GetTime().ToLocalTime()   //这个就是同步后准确的时间，DateTime类型的。