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;        }

董川民