DateTime用法

//今天
DateTime.Now.Date.ToShortDateString();
//昨天,也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(要知道本周第一天就得先知道今天是星期几,从而得知
本周第一天就是几天前的那一天;每一周是从周日始至周六止[0-6])
DateTime.Now.AddDays(Convert.ToDouble((0-Convert.ToInt16
(DateTime.Now.DayOfWeek)))).ToShortDateString();
   //DateTime.Now.DayOfWeek获得今天是本周的第几天(0<=n<=6)
DateTime.Now.AddDays(Convert.ToDouble((6-Convert.ToInt16
(DateTime.Now.DayOfWeek)))).ToShortDateString();
//中文显示星期几
//由于DayOfWeek返回的是数字的星期几,需要把它转换成汉字以方便人们
阅读,有些人会用SWITCH来一个一个地对照,其实我们有更优的策略
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)];//使用它来获取
//上周,同理,一个周是7天,上周就是本周在减去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,本月的第一天是1号,最后一天就是下个月的1号再减一天
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,加上一个月份
DateTime.Parse(Datetime.Now.ToString("yyyy-MM-01")).AddMonths(1).ToShortDateString();
DateTime.Parse(DateTime.Now.ToString("yyyy-MM-01")).AddMonths(2).AddDays(-1).ToShortString();
//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).ToShortString();
//上年度
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是难点,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个季度的第一天减一
DateTime.Parse.(DateTime.Now.AddMonth(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();
//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)
//int days=getDays(System.DateTime.Now);调用即可获得
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.Tuessday:
case System.DayOfWeek.Wednesday:
case System.DayOfWeek.Thursday:
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)
DateTime date1=Convert.ToDateTime("2008-8-8");
DateTime date2=Convert.ToDateTime("2008-10-1");
int days=getDays(date1,date2);
//调用如上即可获得
private int getDays(System.DateTime date1,System.DateTime date2)
{
string m=Microsoft.VisualBasic.DateAndTime.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.Tuesday:
case System.DayOfWeek.Wednesday:
case System.DayOfWeek.Thursday:
case System.DayOfWeek.Friday:
mm=mm+1;
break;
}
}
return mm;
}
//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;
//中国为zh-cn
DateTime myDT=System.DateTime.Now;
Response.Write(myDT.ToString("f",myDTFI));
//获得本周的周六和周日
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=dateAddDays(-6);
last=date;
break;
case System.DayOfWeek.Sunday:
first=date;
last=date.AddDays(6);
break;
}
firstdate=first;
lastdate=last;
}
//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("2008-8-8");
int weeks=dt.DayOfYear/7+1;