asp.net 获取当月的第一天和最后一天示例

时间：2014-08-26 编辑：简简单单来源：一聚教程网

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

复制代码

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

复制代码

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;
            }
        }
    }
}

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