C#中DateTime类

//今天
DateTime.Now.Date.ToShortDateString();
//昨天，就是今天的日期减一
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先知道今天是星期几，从而得知本周的第一天就是几天前的那一天，要注意的是这里的每一周是从周日始至周六止
DateTime.Now.AddDays(Convert.ToDouble((0 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();
DateTime.Now.AddDays(Convert.ToDouble((6 - Convert.ToInt16(DateTime.Now.DayOfWeek)))).ToShortDateString();
//如果你还不明白，再看一下中文显示星期几的方法就应该懂了
//由于DayOfWeek返回的是数字的星期几，我们要把它转换成汉字方便我们阅读，有些人可能会用switch来一个一个地对照，其实不用那么麻烦的 
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，一个周是7天，上周就是本周再减去7天，下周也是一样
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,很多人都会说本月的第一天嘛肯定是1号，最后一天就是下个月一号再减一天。当然这是对的
//一般的写法
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();//最后一天

//巧用C#里ToString的字符格式化更简便
DateTime.Now.ToString("yyyy-MM-01");
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(1).AddDays(-1).ToShortDateString();

//上个月，减去一个月份
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(-1).ToShortDateString();
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddDays(-1).ToShortDateString();
//下个月，加去一个月份
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的字符格式化我们也很容易地算出本年度的第一天和最后一天
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，不用再解释了吧
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，很多人都会觉得这里难点，需要写个长长的过程来判断。其实不用的，我们都知道一年四个季度，一个季度三个月
//首先我们先把日期推到本季度第一个月，然后这个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，本季度的最后一天就是下季度的第一天减一
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();

//如何获得当月有多少天

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

//获取某月的实际工作日(即不包括周六日)

//调用
//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;
}

获得任意两日期之间的有效工作日(不包括周六日) 获得任意两日期之间的有效工作日(不包括周六日)#region 获得任意两日期之间的有效工作日(不包括周六日)

//调用
        //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
格式输出

格式输出#region 格式输出

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

{

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

//中国用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

获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

//调用

DateTime firstdate=System.DateTime.Now;

DateTime lastdate=System.DateTime.Now;

ConvertDateToWeek(date,out firstdate,out lastdate);

获得当前日期是该年度的第几周

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

int weeks = dt.DayOfYear / 7 + 1;