{
  /// <summary>
  /// 
  /// </summary>
  public struct SYSTEMTIME
  {
    public ushort wYear;
    public ushort wMonth;
    public ushort wDayOfWeek;
    public ushort wDay;
    public ushort wHour;
    public ushort wMinute;
    public ushort wSecond;
    public ushort wMilliseconds;
 
    /// <summary>
    /// 從System.DateTime轉換。
    /// </summary>
    /// <param name="time">System.DateTime類型的時間。</param>
    public void FromDateTime(DateTime time)
    {
      wYear = (ushort)time.Year;
      wMonth = (ushort)time.Month;
      wDayOfWeek = (ushort)time.DayOfWeek;
      wDay = (ushort)time.Day;
      wHour = (ushort)time.Hour;
      wMinute = (ushort)time.Minute;
      wSecond = (ushort)time.Second;
      wMilliseconds = (ushort)time.Millisecond;
    }
    /// <summary>
    /// 轉換為System.DateTime類型。
    /// </summary>
    /// <returns></returns>
    public DateTime ToDateTime()
    {
      return new DateTime(wYear, wMonth, wDay, wHour, wMinute, wSecond, wMilliseconds);
    }
    /// <summary>
    /// 靜態(tài)方法。轉換為System.DateTime類型。
    /// </summary>
    /// <param name="time">SYSTEMTIME類型的時間。</param>
    /// <returns></returns>
    public static DateTime ToDateTime(SYSTEMTIME time)
    {
      return time.ToDateTime();
    }
  }
 public class Win32API
  {
    [DllImport("Kernel32.dll")]
    public static extern bool SetLocalTime( ref SYSTEMTIME Time );
    [DllImport("Kernel32.dll")]
    public static extern void GetLocalTime(ref SYSTEMTIME Time);
  }
}

private void button1_Click(object sender, System.EventArgs e)
{
  //取得當前系統(tǒng)時間
  DateTime t = DateTime.Now;
  //在當前時間上加上一周
  t = t.AddDays(7);
  //轉換System.DateTime到SYSTEMTIME
  SYSTEMTIME st = new SYSTEMTIME();
  st.FromDateTime(t);
  //調用Win32 API設置系統(tǒng)時間
  Win32API.SetLocalTime(ref st);
  //顯示當前時間
  MessageBox.Show(DateTime.Now.ToString());
}