c#中DateTime類

//今天
DateTime.Now.Date.ToShortDateString();
//昨天，就是今天的日期減一
DateTime.Now.AddDays(-1).ToShortDateString();
//明天，同理，加一
DateTime.Now.AddDays(1).ToShortDateString();

//本周(要知道本周的第一天就得Crowdsourced Security Testing道今天是星期幾，從而得知本周的第一天就是幾天前的那一天，要注意的是這裡的每一周是從周日始至周六止
DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();
DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();
//如果你還不明白，再看一下中文顯示星期幾的方法就應該懂了
//由於DayOfWeek返回的是數位星期幾，我們要把它轉換成漢字方便我們閱讀，有些人可能會用switch來一個一個地對照，其實不用那麼麻煩的 
string[] Day = new string[] { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };
Day[Convert.ToInt16(DateTime.Now.DayOfWeek)];

//上周，同理，一個周是7天，上周就是本周再減去7天，下周也是一樣
DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString();
DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek))) - 7).ToShortDateString();
//下周
DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();
DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek))) + 7).ToShortDateString();
//本月,很多人都會說本月的第一天嘛肯定是1號，最後一天就是下個月一號再減一天。當然這是對的
//一般的寫法
DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + "1"; //第一天
DateTime.Parse(DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString() + "1").AddMonths(1).AddDays(-1).ToShortDateString();//最後一天

//巧用C#裡ToString的字元格式設定化更簡便
DateTime.Now.ToString("yyyy-MM-01");
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).AddDays(-1).ToShortDateString();

//上個月，減去一個月份
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(-1).ToShortDateString();
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();
//下個月，加去一個月份
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).ToShortDateString();
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(2).AddDays(-1).ToShortDateString();
//7天后
DateTime.Now.Date.ToShortDateString();
DateTime.Now.AddDays(7).ToShortDateString();
//7天前
DateTime.Now.AddDays(-7).ToShortDateString();
DateTime.Now.Date.ToShortDateString();

//本年度，用ToString的字元格式設定化我們也很容易地算出本年度的第一天和最後一天
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).ToShortDateString();
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(1).AddDays(-1).ToShortDateString();
//上年度，不用再解釋了吧
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(-1).ToShortDateString();
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddDays(-1).ToShortDateString();
//下年度
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(1).ToShortDateString();
DateTime.Parse(DateTime.Now.ToString("yyyy-01-01")).AddYears(2).AddDays(-1).ToShortDateString();

//本季度，很多人都會覺得這裡痛點，需要寫個長長的過程來判斷。其實不用的，我們都知道一年四個季度，一個季度三個月
//首先我們先把日期推到本季度第一個月，然後這個月的第一天就是本季度的第一天了
DateTime.Now.AddMonths(0 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");
//同理，本季度的最後一天就是下季度的第一天減一
DateTime.Parse(DateTime.Now.AddMonths(3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();
//下季度
DateTime.Now.AddMonths(3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");
DateTime.Parse(DateTime.Now.AddMonths(6 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();
//上季度
DateTime.Now.AddMonths(-3 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01");
DateTime.Parse(DateTime.Now.AddMonths(0 - ((DateTime.Now.Month - 1) % 3)).ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString(); 

//如何獲得當月有多少天

int m=System.DateTime.DaysInMonth(System.DateTime.Now.Year,System.DateTime.Now.Month);

//擷取某月的實際工作日(即不包括周六日)

//調用
//int days =getDays(System.DateTime.Now));
private int getDays(System.DateTime date1)
{
    int m=System.DateTime.DaysInMonth(date1.Year,date1.Month);
    int mm=0;
    for(int i=1;i<=m;i++)
    {
        System.DateTime date=Convert.ToDateTime(date1.Year+"-"+date1.Month+"-"+i);
        switch (date.DayOfWeek)
        {
            case System.DayOfWeek.Monday:
            case System.DayOfWeek.Thursday:
            case System.DayOfWeek.Tuesday:
            case System.DayOfWeek.Wednesday:
            case System.DayOfWeek.Friday:
                mm=mm+1;
                break;

        }                
    }
    return mm;
}

獲得任意兩日期之間的有效工作日(不包括周六日) 獲得任意兩日期之間的有效工作日(不包括周六日)#region 獲得任意兩日期之間的有效工作日(不包括周六日)

//調用
        //DateTime date1=Convert.ToDateTime("2005-10-20");
        //DateTime date2=Convert.ToDateTime("2005-11-01");
        //int days =getDays(date1,date2);
        private int getDays(System.DateTime date1,System.DateTime date2)
        {
            string m=DateDiff(EnumDateCompare.day,date1,date2).ToString("f0");
            
            int mm=0;
            for(int i=0;i<=Convert.ToInt32(m);i++)
            {
                System.DateTime date=Convert.ToDateTime(date1.AddDays(i));
                switch (date.DayOfWeek)
                {
                    case System.DayOfWeek.Monday:
                    case System.DayOfWeek.Thursday:
                    case System.DayOfWeek.Tuesday:
                    case System.DayOfWeek.Wednesday:
                    case System.DayOfWeek.Friday:
                        mm=mm+1;
                        break;
                }                
            }
            return mm;
        }
        #endregion
格式輸出

格式輸出#region 格式輸出

        private void Page_Load(object sender, System.EventArgs e)

       {            

System.Globalization.DateTimeFormatInfo myDTFI = new System.Globalization.CultureInfo( "en-US", false ).DateTimeFormat;

//中國用zh-cn

            DateTime myDT =System.DateTime.Now;

            Response.Write(myDT.ToString("f",myDTFI));

            /**//**//**//*

            This code produces the following output.

            FORMAT  en-US EXAMPLE

            CHAR    VALUE OF ASSOCIATED PROPERTY, IF ANY

              d     1/3/2002                    M/d/yyyy (ShortDatePattern)  

            D     Thursday, January 03, 2002                    dddd, MMMM dd, yyyy (LongDatePattern)

              f     Thursday, January 03, 2002 12:00 AM 

             F     Thursday, January 03, 2002 12:00:00 AM                    dddd, MMMM dd, yyyy h:mm:ss tt (FullDateTimePattern)

              g     1/3/2002 12:00 AM

              G     1/3/2002 12:00:00 AM

              m     January 03                   MMMM dd (MonthDayPattern)

              M     January 03                    MMMM dd (MonthDayPattern)

              r     Thu, 03 Jan 2002 00:00:00 GMT                    ddd, dd MMM yyyy HH':'mm':'ss 'GMT' (RFC1123Pattern)

              R     Thu, 03 Jan 2002 00:00:00 GMT                    ddd, dd MMM yyyy HH':'mm':'ss 'GMT' (RFC1123Pattern)

              s     2002-01-03T00:00:00                    yyyy'-'MM'-'dd'T'HH':'mm':'ss (SortableDateTimePattern)

              t     12:00 AM                    h:mm tt (ShortTimePattern)

              T     12:00:00 AM                    h:mm:ss tt (LongTimePattern)

              u     2002-01-03 00:00:00Z                    yyyy'-'MM'-'dd HH':'mm':'ss'Z' (UniversalSortableDateTimePattern)

              U     Thursday, January 03, 2002 8:00:00 AM

              y     January, 2002                    MMMM, yyyy (YearMonthPattern)

              Y     January, 2002                    MMMM, yyyy (YearMonthPattern)

            */ 

       }

                #endregion

獲得本周的周六和周日

ConvertDateToWeek#region ConvertDateToWeek

        public static void ConvertDateToWeek(DateTime date,out DateTime firstdate,out DateTime lastdate)

        {

                DateTime first=System.DateTime.Now;

            DateTime last=System.DateTime.Now;

            switch (date.DayOfWeek)

            {       case System.DayOfWeek.Monday:

                    first=date.AddDays(-1);

                    last=date.AddDays(5);

                    break;

                case System.DayOfWeek.Tuesday:

                    first=date.AddDays(-2);

                    last=date.AddDays(4);

                    break;

                case System.DayOfWeek.Wednesday:

                    first=date.AddDays(-3);

                    last=date.AddDays(3);

                    break;

                case System.DayOfWeek.Thursday:

                    first=date.AddDays(-4);

                    last=date.AddDays(2);

                    break;

                case System.DayOfWeek.Friday:

                    first=date.AddDays(-5);

                    last=date.AddDays(1);

                    break;

                case System.DayOfWeek.Saturday:

                    first=date.AddDays(-6);

                    last=date;

                    break;

                case System.DayOfWeek.Sunday:

                    first=date;

                    last=date.AddDays(6);

                    break; 

                           }

            firstdate=first;

            lastdate=last;

        }

        #endregion

    //調用

DateTime firstdate=System.DateTime.Now;

    DateTime lastdate=System.DateTime.Now;

ConvertDateToWeek(date,out firstdate,out lastdate);

獲得當前日期是該年度的第幾周

DateTime dt = Convert.ToDateTime("2006-05-01");

int weeks = dt.DayOfYear / 7 + 1;