獲取去年當天的當天日期嗎？

Question

我想找到一種方法來從去年匹配日期的日期，

因此，例如今天是7月的第四個星期五，同樣的日期會是去年？

我正在從一家餐廳獲得銷售額，我需要在同一天針對去年的銷售額進行覈對。

Answer 1

如上所述，問題沒有答案，因爲月份開始於不同年份的不同日子（更不用說閏年併發症）。

僅僅減去364天就足夠了，這正好是52周，所以你最終得到的是同一個星期的日子？

Answer 2

DateTime now = DateTime.Now.Date; 
DateTime sameDayLastYear = new DateTime(now.Year - 1, now.Month, now.Day); 

當您嘗試設置時間爲2011年2月29日

DateTime leapDay = new DateTime(2012, 2, 29); 
DateTime sameleapDayLastYear = new DateTime(leapDay.Year - 1, leapDay.Month, leapDay.Day); 

Answer 3

如果你正在尋找你會遇到一個閏年，即下面的代碼中的問題會拋出異常對於是在一年內每月的第N特定工作日，這個代碼可以幫助：

using System; 

class NthWeekDayOfMonth 
{ 
    public 
    NthWeekDayOfMonth(DateTime date) 
    { 
     this.date = date; 
    } 

    public 
    NthWeekDayOfMonth(int n, DayOfWeek weekDay, int month, int year) 
    { 
     DateTime firstDayOfMonth = new DateTime(year, month, 1); 
     if (weekDay < firstDayOfMonth.DayOfWeek) 
     { 
      this.date = firstDayOfMonth.AddDays((n - 1) * 7 + weekDay + 7 - firstDayOfMonth.DayOfWeek); 
     } 
     else 
     { 
      this.date = firstDayOfMonth.AddDays((n - 1) * 7 + weekDay - firstDayOfMonth.DayOfWeek); 
     } 
    } 

    public int 
    Month 
    { 
     get { return date.Month; } 
    } 

    public DayOfWeek 
    WeekDay 
    { 
     get { return date.DayOfWeek; } 
    } 

    public int 
    N 
    { 
     get { return (date.Day - 1)/7 + 1; } 
    } 

    public int 
    Year 
    { 
     get { return date.Year; } 
    } 

    public DateTime 
    Date 
    { 
     get { return date; } 
    } 

    private DateTime 
    date; 
} 

class Program 
{ 
    static void Main(string[] args) 
    { 
     for (DateTime d = new DateTime(2010, 7, 1); d <= new DateTime(2010, 7, 31); d = d.AddDays(1)) 
     { 
      NthWeekDayOfMonth thisYear = new NthWeekDayOfMonth(d); 
      NthWeekDayOfMonth lastYear = new NthWeekDayOfMonth(thisYear.N, thisYear.WeekDay, thisYear.Month, thisYear.Year - 1); 
      Console.WriteLine("{0}th {1} of {2} in {3}: {4} - in {5}: {6}", thisYear.N, thisYear.WeekDay, thisYear.Month, thisYear.Year, thisYear.Date, lastYear.Year, lastYear.Date); 
     } 
    } 
}