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

Question

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.

var RequestIds = (from r in rdc.request 
                  where r.dteCreated >= LastMonthsFirstDate && 
                  r.dteCreated <= LastMonthsLastDate 
                  select r.intRequestId);

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

Answer 1

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

dFirstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );

Then subtract a day to get end of last month

dLastDayOfLastMonth = dFirstDayOfThisMonth.AddDays (-1);

Then subtract a month to get first day of previous month

dFirstDayOfLastMonth = dFirstDayOfThisMonth.AddMonths(-1);

Answer 2

DateTime LastMonthLastDate = DateTime.Today.AddDays(0 - DateTime.Today.Day);
DateTime LastMonthFirstDate = LastMonthLastDate.AddDays(1 - LastMonthLastDate.Day);

Answer 3

var first = new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1).AddMonths(-1);
var last = new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1).AddDays(-1);

In-line them if you want.

Answer 4

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());

Answer 5

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.

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);

Answer 6

An approach using extension methods:

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 );
    }
}

See this link http://www.codeplex.com/fluentdatetime for some inspired DateTime extensions.

Answer 7

EDIT: This is not the way to do it!
If today.Month - 1 = 0, as in Jan, this will throw an exception. This is clearly a case where being clever gets you in trouble!

A little simpler than the accepted answer:

var today = DateTime.Today
var first = new DateTime(today.Year, today.Month - 1, 1);
var last  = new DateTime(today.Year, today.Month, 1).AddDays(-1);

Saves an extra DateTime creation.

Answer 8

using Fluent DateTime http://fluentdatetime.codeplex.com/

        var lastMonth = 1.Months().Ago().Date;
        var firstDayOfMonth = lastMonth.FirstDayOfMonth();
        var lastDayOfMonth = lastMonth.LastDayOfMonth();

Answer 9

thnxzzzzzzzzz Andrew Robinson