c#中DateTime类 - 润新知

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;
```
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原文地址：https://www.cnblogs.com/luluping/p/1561388.html