asp.net 获取当月的第一天和最后一天示例

ASP.NET(C#)返回每个月的第一天和最后一天要怎么来做呢，我们下文整理了不少例子，然后根据例子做了一个智能判断每个月有多少天，无需你计算，本函数将替你完成： 希望对各位有帮助。

 

最简单获取当月第一天和最后一天 代码如下

代码如下	复制代码
DateTime now = DateTime.Now; DateTime dt1 = new DateTime(now.Year, now.Month, 1); DateTime dt2 = d1.AddMonths(1).AddDays(-1);

dt1是本月的第一天，dt2本月的最后一天，
最后一天的算法是：得到本月的第一天然后增加一月，再减去一天.

例子

代码如下

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DateTime dt = DateTime.Now;  //本月第一天时间  DateTime dt_First = dt.AddDays(-(dt.Day) + 1);  Label1.Text = dt_First.ToString("yyyy-MM-dd");  //将本月月数+1  DateTime dt2 = dt.AddMonths(1);  //本月最后一天时间  DateTime dt_Last = dt2.AddDays(-(dt.Day));  Label2.Text = dt_Last.ToString("yyyy-MM-dd");  int weeknow = Convert.ToInt32(System.DateTime.Now.DayOfWeek);  int daydiff = (-1) * weeknow + 1;  int dayadd = 7 - weeknow;

上面我们都需要手来写，下面代码可以实现智能判断了

例子,智能判断每个月有多少天，无需你计算，本函数将替你完成：

代码如下

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using System; namespace DotNet.Utilities {     public class DateFormat     {         //返回每月的第一天和最后一天         public static void ReturnDateFormat(int month, out string firstDay, out string lastDay)         {             int year = DateTime.Now.Year + month / 12;             if (month != 12)             {                 month = month % 12;             }             switch (month)             {                 case 1:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-0" + month + "-31");                     break;                 case 2:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     if (DateTime.IsLeapYear(DateTime.Now.Year))                         lastDay = DateTime.Now.ToString(year + "-0" + month + "-29");                     else                         lastDay = DateTime.Now.ToString(year + "-0" + month + "-28");                     break;                 case 3:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString("yyyy-0" + month + "-31");                     break;                 case 4:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-0" + month + "-30");                     break;                 case 5:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-0" + month + "-31");                     break;                 case 6:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-0" + month + "-30");                     break;                 case 7:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-0" + month + "-31");                     break;                 case 8:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-0" + month + "-31");                     break;                 case 9:                     firstDay = DateTime.Now.ToString(year + "-0" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-0" + month + "-30");                     break;                 case 10:                     firstDay = DateTime.Now.ToString(year + "-" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-" + month + "-31");                     break;                 case 11:                     firstDay = DateTime.Now.ToString(year + "-" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-" + month + "-30");                     break;                 default:                     firstDay = DateTime.Now.ToString(year + "-" + month + "-01");                     lastDay = DateTime.Now.ToString(year + "-" + month + "-31");                     break;             }         }     } }