blocks|key|1617188|text|我过去的做法是先得到这个月的第一天|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1617189|dFirstDayOfThisMonth+=+DateTime.Today.AddDays(+-+(+DateTime.Today.Day+-+1+)+);|code-block|syntax|javascript|1617190|然后减去一天得到上个月的月底|1617191|dLastDayOfLastMonth+=+dFirstDayOfThisMonth.AddDays+(-1);|1617192|然后减去一个月得到上个月的第一天。|1617193|dFirstDayOfLastMonth+=+dFirstDayOfThisMonth.AddMonths(-1);|1617194|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

The way I've done this in the past is first get the first day of this month

<pre><code>dFirstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );
</code></pre>

Then subtract a day to get end of last month

<pre><code>dLastDayOfLastMonth = dFirstDayOfThisMonth.AddDays (-1);
</code></pre>

Then subtract a month to get first day of previous month

<pre><code>dFirstDayOfLastMonth = dFirstDayOfThisMonth.AddMonths(-1);
</code></pre>

blocks|key|1617198|text|DateTime+LastMonthLastDate+=+DateTime.Today.AddDays(0+-+DateTime.Today.Day);
DateTime+LastMonthFirstDate+=+LastMonthLastDate.AddDays(1+-+LastMonthLastDate.Day);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1617199|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>DateTime LastMonthLastDate = DateTime.Today.AddDays(0 - DateTime.Today.Day);
DateTime LastMonthFirstDate = LastMonthLastDate.AddDays(1 - LastMonthLastDate.Day);
</code></pre>

blocks|key|1617263|text|var+today+=+DateTime.Today;
var+month+=+new+DateTime(today.Year,+today.Month,+1);+++++++
var+first+=+month.AddMonths(-1);
var+last+=+month.AddDays(-1);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1617264|如果你真的需要一到两行代码，就把它们内联起来。|unstyled|1617265|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>var today = DateTime.Today;
var month = new DateTime(today.Year, today.Month, 1); 
var first = month.AddMonths(-1);
var last = month.AddDays(-1);
</code></pre>

In-line them if you really need one or two lines.

blocks|key|1617269|text|DateTime+now+=+DateTime.Now;
int+prevMonth+=+now.AddMonths(-1).Month;
int+year+=+now.AddMonths(-1).Year;
int+daysInPrevMonth+=+DateTime.DaysInMonth(year,+prevMonth);
DateTime+firstDayPrevMonth+=+new+DateTime(year,+prevMonth,+1);
DateTime+lastDayPrevMonth+=+new+DateTime(year,+prevMonth,+daysInPrevMonth);
Console.WriteLine("{0}+{1}",+firstDayPrevMonth.ToShortDateString(),
++lastDayPrevMonth.ToShortDateString());|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1617270|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>DateTime now = DateTime.Now;
int prevMonth = now.AddMonths(-1).Month;
int year = now.AddMonths(-1).Year;
int daysInPrevMonth = DateTime.DaysInMonth(year, prevMonth);
DateTime firstDayPrevMonth = new DateTime(year, prevMonth, 1);
DateTime lastDayPrevMonth = new DateTime(year, prevMonth, daysInPrevMonth);
Console.WriteLine("{0} {1}", firstDayPrevMonth.ToShortDateString(),
 lastDayPrevMonth.ToShortDateString());
</code></pre>

blocks|key|1402669|text|如果您的日期时间不是严格的日历日期，那么您应该考虑使用结束日期排除比较……这将防止您错过在1月31日期间创建的任何请求。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1402670|DateTime+now+=+DateTime.Now;
DateTime+thisMonth+=+new+DateTime(now.Year,+now.Month,+1);
DateTime+lastMonth+=+thisMonth.AddMonths(-1);

var+RequestIds+=+rdc.request
++.Where(r+=>+lastMonth+<=+r.dteCreated)
++.Where(r+=>+r.dteCreated+<+thisMonth)
++.Select(r+=>+r.intRequestId);|code-block|syntax|javascript|1402671|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If there's any chance that your datetimes aren't strict calendar dates, you should consider using enddate exclusion comparisons...
This will prevent you from missing any requests created during the date of Jan 31.

<pre><code>DateTime now = DateTime.Now;
DateTime thisMonth = new DateTime(now.Year, now.Month, 1);
DateTime lastMonth = thisMonth.AddMonths(-1);

var RequestIds = rdc.request
 .Where(r =&gt; lastMonth &lt;= r.dteCreated)
 .Where(r =&gt; r.dteCreated &lt; thisMonth)
 .Select(r =&gt; r.intRequestId);
</code></pre>

blocks|key|1617388|text|使用扩展方法的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1617389|class+Program
{
++++static+void+Main(string[]+args)
++++{
++++++++DateTime+t+=+DateTime.Now;

++++++++DateTime+p+=+t.PreviousMonthFirstDay();
++++++++Console.WriteLine(+p.ToShortDateString()+);

++++++++p+=+t.PreviousMonthLastDay();
++++++++Console.WriteLine(+p.ToShortDateString()+);


++++++++Console.ReadKey();
++++}
}


public+static+class+Helpers
{
++++public+static+DateTime+PreviousMonthFirstDay(+this+DateTime+currentDate+)
++++{
++++++++DateTime+d+=+currentDate.PreviousMonthLastDay();

++++++++return+new+DateTime(+d.Year,+d.Month,+1+);
++++}

++++public+static+DateTime+PreviousMonthLastDay(+this+DateTime+currentDate+)
++++{
++++++++return+new+DateTime(+currentDate.Year,+currentDate.Month,+1+).AddDays(+-1+);
++++}
}|code-block|syntax|javascript|1617390|有关DateTime扩展的一些启发，请参阅此链接http://www.codeplex.com/fluentdatetime。|offset|length|1617391|entityMap|0|LINK|mutability|MUTABLE|url|http://www.codeplex.com/fluentdatetime^0|0|0|O|12|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

An approach using extension methods:

<pre><code>class Program
{
 static void Main(string[] args)
 {
 DateTime t = DateTime.Now;

 DateTime p = t.PreviousMonthFirstDay();
 Console.WriteLine( p.ToShortDateString() );

 p = t.PreviousMonthLastDay();
 Console.WriteLine( p.ToShortDateString() );


 Console.ReadKey();
 }
}


public static class Helpers
{
 public static DateTime PreviousMonthFirstDay( this DateTime currentDate )
 {
 DateTime d = currentDate.PreviousMonthLastDay();

 return new DateTime( d.Year, d.Month, 1 );
 }

 public static DateTime PreviousMonthLastDay( this DateTime currentDate )
 {
 return new DateTime( currentDate.Year, currentDate.Month, 1 ).AddDays( -1 );
 }
}
</code></pre>

See this link
<a href="http://www.codeplex.com/fluentdatetime" rel="nofollow noreferrer">http://www.codeplex.com/fluentdatetime</a>
for some inspired DateTime extensions.

blocks|key|1402723|text|使用Fluent+DateTime+https://github.com/FluentDateTime/FluentDateTime|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1402724|++++++++var+lastMonth+=+1.Months().Ago().Date;
++++++++var+firstDayOfMonth+=+lastMonth.FirstDayOfMonth();
++++++++var+lastDayOfMonth+=+lastMonth.LastDayOfMonth();|code-block|syntax|javascript|1402725|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/FluentDateTime/FluentDateTime^0|I|1C|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

using Fluent DateTime <a href="https://github.com/FluentDateTime/FluentDateTime" rel="noreferrer">https://github.com/FluentDateTime/FluentDateTime</a>

<pre><code> var lastMonth = 1.Months().Ago().Date;
 var firstDayOfMonth = lastMonth.FirstDayOfMonth();
 var lastDayOfMonth = lastMonth.LastDayOfMonth();
</code></pre>

blocks|key|1617457|text|电子商务中的典型用例是信用卡到期日期，MM/yy。减去一秒而不是一天。否则，该卡将在到期月份的整个最后一天显示为过期。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1617458|DateTime+expiration+=+DateTime.Parse("07/2013");
DateTime+endOfTheMonthExpiration+=+new+DateTime(
++expiration.Year,+expiration.Month,+1).AddMonths(1).AddSeconds(-1);|code-block|syntax|javascript|1617459|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

The canonical use case in e-commerce is credit card expiration dates, MM/yy. Subtract one second instead of one day. Otherwise the card will appear expired for the entire last day of the expiration month.

<pre><code>DateTime expiration = DateTime.Parse("07/2013");
DateTime endOfTheMonthExpiration = new DateTime(
 expiration.Year, expiration.Month, 1).AddMonths(1).AddSeconds(-1);
</code></pre>

blocks|key|1402788|text|我使用这个简单的一行代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1402789|public+static+DateTime+GetLastDayOfPreviousMonth(this+DateTime+date)
{
++++return+date.AddDays(-date.Day);
}|code-block|syntax|javascript|1402790|请注意，它保留了时间。|1402791|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I use this simple one-liner:

<pre><code>public static DateTime GetLastDayOfPreviousMonth(this DateTime date)
{
 return date.AddDays(-date.Day);
}
</code></pre>

Be aware, that it retains the time.

blocks|key|1617544|text|以下是Mike+W的回答：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1617545|internal+static+DateTime+GetPreviousMonth(bool+returnLastDayOfMonth)
{
++++DateTime+firstDayOfThisMonth+=+DateTime.Today.AddDays(+-+(+DateTime.Today.Day+-+1+)+);
++++DateTime+lastDayOfLastMonth+=+firstDayOfThisMonth.AddDays+(-1);
++++if+(returnLastDayOfMonth)+return+lastDayOfLastMonth;
++++return+firstDayOfThisMonth.AddMonths(-1);
}|code-block|syntax|javascript|1617546|你可以这样称呼它：|1617547|dateTimePickerFrom.Value+=+GetPreviousMonth(false);
dateTimePickerTo.Value+=+GetPreviousMonth(true);|1617548|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

This is a take on Mike W's answer:

<pre><code>internal static DateTime GetPreviousMonth(bool returnLastDayOfMonth)
{
 DateTime firstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );
 DateTime lastDayOfLastMonth = firstDayOfThisMonth.AddDays (-1);
 if (returnLastDayOfMonth) return lastDayOfLastMonth;
 return firstDayOfThisMonth.AddMonths(-1);
}
</code></pre>

You can call it like so:

<pre><code>dateTimePickerFrom.Value = GetPreviousMonth(false);
dateTimePickerTo.Value = GetPreviousMonth(true);
</code></pre>

I can't think of an easy one or two liner that would get the previous months first day and last day.

I am LINQ-ifying a survey web app, and they squeezed a new requirement in.

The survey must include all of the service requests for the previous month. So if it is April 15th, I need all of Marches request ids.

<pre><code>var RequestIds = (from r in rdc.request 
 where r.dteCreated &gt;= LastMonthsFirstDate &amp;&amp; 
 r.dteCreated &lt;= LastMonthsLastDate 
 select r.intRequestId);
</code></pre>

I just can't think of the dates easily without a switch. Unless I'm blind and overlooking an internal method of doing it.

Get the previous month's first and last day dates in c#

我不能想出一个简单的一两个班轮可以得到前几个月的第一天和最后一天。我正在LINQ-一个调查网络应用程序，他们挤入了一个新的要求。调查必须包括上个月的所有服务请求。所以如果是4月15日，我需要所有的游行请求ids。var RequestIds = (from r in rdc.request               ...

问在c#中获取上个月的首日和末日日期
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问在c#中获取上个月的首日和末日日期
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