C#关于DateTime得到的当前时间的格式和用法

DateTime.Now.ToShortTimeString() 
DateTime dt = DateTime.Now; 
dt.ToString();//2005-11-5 13:21:25 
dt.ToFileTime().ToString();//127756416859912816 
dt.ToFileTimeUtc().ToString();//127756704859912816 
dt.ToLocalTime().ToString();//2005-11-5 21:21:25 
dt.ToLongDateString().ToString();//2005年11月5日 
dt.ToLongTimeString().ToString();//13:21:25 
dt.ToOADate().ToString();//38661.5565508218 
dt.ToShortDateString().ToString();//2005-11-5 
dt.ToShortTimeString().ToString();//13:21 
dt.ToUniversalTime().ToString();//2005-11-5 5:21:25 
dt.Year.ToString();//2005 
dt.Date.ToString();//2005-11-5 0:00:00 
dt.DayOfWeek.ToString();//Saturday 
dt.DayOfYear.ToString();//309 
dt.Hour.ToString();//13 
dt.Millisecond.ToString();//441 
dt.Minute.ToString();//30 
dt.Month.ToString();//11 
dt.Second.ToString();//28 
dt.Ticks.ToString();//632667942284412864 
dt.TimeOfDay.ToString();//13:30:28.4412864 
dt.ToString();//2005-11-5 13:47:04 
dt.AddYears(1).ToString();//2006-11-5 13:47:04 
dt.AddDays(1.1).ToString();//2005-11-6 16:11:04 
dt.AddHours(1.1).ToString();//2005-11-5 14:53:04 
dt.AddMilliseconds(1.1).ToString();//2005-11-5 13:47:04 
dt.AddMonths(1).ToString();//2005-12-5 13:47:04 
dt.AddSeconds(1.1).ToString();//2005-11-5 13:47:05 
dt.AddMinutes(1.1).ToString();//2005-11-5 13:48:10 
dt.AddTicks(1000).ToString();//2005-11-5 13:47:04 
dt.CompareTo(dt).ToString();//0 
dt.Add(?).ToString();//问号为一个时间段 
dt.Equals("2005-11-6 16:11:04").ToString();//False 
dt.Equals(dt).ToString();//True 
dt.GetHashCode().ToString();//1474088234 
dt.GetType().ToString();//System.DateTime 
dt.GetTypeCode().ToString();//DateTime

dt.GetDateTimeFormats('s')[0].ToString();//2005-11-05T14:06:25 
dt.GetDateTimeFormats('t')[0].ToString();//14:06 
dt.GetDateTimeFormats('y')[0].ToString();//2005年11月 
dt.GetDateTimeFormats('D')[0].ToString();//2005年11月5日 
dt.GetDateTimeFormats('D')[1].ToString();//2005 11 05 
dt.GetDateTimeFormats('D')[2].ToString();//星期六 2005 11 05 
dt.GetDateTimeFormats('D')[3].ToString();//星期六 2005年11月5日 
dt.GetDateTimeFormats('M')[0].ToString();//11月5日 
dt.GetDateTimeFormats('f')[0].ToString();//2005年11月5日 14:06 
dt.GetDateTimeFormats('g')[0].ToString();//2005-11-5 14:06 
dt.GetDateTimeFormats('r')[0].ToString();//Sat, 05 Nov 2005 14:06:25 GMT 
string.Format("{0:d}",dt);//2005-11-5 
string.Format("{0}",dt);//2005年11月5日 
string.Format("{0:f}",dt);//2005年11月5日 14:23 
string.Format("{0:F}",dt);//2005年11月5日 14:23:23 
string.Format("{0:g}",dt);//2005-11-5 14:23 
string.Format("{0:G}",dt);//2005-11-5 14:23:23 
string.Format("{0:M}",dt);//11月5日 
string.Format("{0:R}",dt);//Sat, 05 Nov 2005 14:23:23 GMT 
string.Format("{0:s}",dt);//2005-11-05T14:23:23 
string.Format("{0:t}",dt);//14:23 
string.Format("{0:T}",dt);//14:23:23 
string.Format("{0:u}",dt);//2005-11-05 14:23:23Z 
string.Format("{0:U}",dt);//2005年11月5日 6:23:23 
string.Format("{0:Y}",dt);//2005年11月 
string.Format("{0}",dt);//2005-11-5 14:23:23 
string.Format("{0:yyyyMMddHHmmssffff}",dt); 
计算2个日期之间的天数差 
----------------------------------------------- 
DateTime dt1 = Convert.DateTime("2007-8-1"); 
DateTime dt2 = Convert.DateTime("2007-8-15"); 
TimeSpan span = dt2.Subtract(dt1); 
int dayDiff = span.Days + 1; 
计算某年某月的天数 
----------------------------------------------- 
int days = DateTime.DaysInMonth(2007, 8); 
days = 31; 
给日期增加一天、减少一天 
----------------------------------------------- 
DateTime dt =DateTime.Now; 
dt.AddDays(1); //增加一天 
dt.AddDays(-1);//减少一天 
其它年份方法类似... 
Oracle SQL里转换日期函数 
----------------------------------------------- 
to_date("2007-6-6",'YYYY-MM-DD"); 
to_date("2007/6/6",'yyyy/mm/dd"); 
如下一组数据,如何查找表里包含9月份的记录: 
CGGC_STRATDATE CGGC_ENDDATE 
========================================= 
2007-8-4 2007-9-5 
2007-9-5 2007-9-20 
2007-9-22 2007-10-5 
SELECT * FROM TABLE 
(TO_DATE('2007/9/1','yyyy/mm/dd') BETWEEN CGGC_STRATDATE 
AND CGGC_ENDDATE OR CGGC_STRATDATE >=TO_DATE('2007/9/1','yyyy/mm/dd') 
AND CGGC_ENDDATE<=TO_DATE('2007/9/30','yyyy/mm/dd') " 
OR TO_DATE('2007/9/30','yyyy/mm/dd') BETWEEN CGGC_STRATDATE 
AND CGGC_ENDDATE) ORDER BY CGGC_STRATDATE ASC

//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;