C#中时间相关知识点小结

c#中时间相关知识点小结

一、月份英文简写

  datetime dt = datetime.now;
  string mm = dt.addmonths(-1).tostring("mmm", new system.globalization.cultureinfo("en-us"));//月英文缩写：jul

二、当月第一天和最后一天

datetime thismonth_frist = datetime.now.adddays(1 - datetime.now.day).date;
datetime thismonth_last = datetime.now.adddays(1 - datetime.now.day).date.addmonths(1).addseconds(-1);

三、上月第一天和最后一天

datetime today = datetime.today;//当天时间
datetime thismonth = new datetime(today.year, today.month, 1);//当前月第一天时间
datetime lastmonth_first = thismonth.addmonths(-1);//上月第一天时间
datetime lastmonth_last = thismonth.adddays(-1);//上月最后一天时间

四、本周第几天

int daysinweek1 = (int)datetime.now.dayofweek;//注意：此处周,日时返回0，
int daysinweek2 = (int)datetime.now.dayofweek == 0 ? 7 : (int)datetime.now.dayofweek;//当前周第几天,注释:周日为0

五、本月第几周

int a = weekofmonth(datetime.now, false);//

六、本年第几周

     private int weekofyear()
        {
            var dt = datetime.now;
            int firstweekend = convert.toint32(datetime.parse(dt.year + "-1-1").dayofweek);
            int weekday = firstweekend == 0 ? 1 : (7 - firstweekend + 1);
            int currentday = dt.dayofyear;
            int current_week = convert.toint32(math.ceiling((currentday - weekday) / 7.0)) + 1;
            return current_week;
        }

七、前几周的周一和周日

 private void fedayinlastweek()
        {
            int n = 3;//前几周参数
            datetime today = datetime.now;
            int daysinweek = (int)today.dayofweek == 0 ? 7 : (int)today.dayofweek;//当前周第几天,注释:周日为0
           
            for (int i = n; i > 0; i--)
            {
                //起始日期
                datetime firstday = today.adddays(1 - (7 * i + daysinweek));
                datetime lastday = today.adddays(7 - (7 * i + daysinweek));
            }
        }

八、本周一和当前日

   private void fristdaytonowinthisweek()
        {
            int daysinweek = (int)datetime.now.dayofweek == 0 ? 7 : (int)datetime.now.dayofweek;//当前周第几天,注释:周日为0
            //起始日期
            datetime firstday = datetime.now.adddays(1 - daysinweek);
            datetime lastday = datetime.now;
        }