From: ara.t.howard@...
Date: 2006-09-22T04:36:37+09:00
Subject: Re: Calculate last day of month

On Fri, 22 Sep 2006, Paul Lutus wrote:

> Hunter Walker wrote:
>
>> This is probably an easy one for somebody, but I couldn't figure it out
>> using the Date class in the documentation.
>>
>> How do I return the date for the last day of this month (September in this
>> example)?
>
> Easy: Construct a date for the first day of the following month, then
> subtract one day and read the resulting components.
>
> Hard: construct a date for the first day of the target month, then add days
> unitil the month number changes. Then go back one.
>
> I think I know which option you'll choose. :)

except you have to handle december specially - else you'll end up with the
with the wrong year.

easiest is probably:

harp:~ > cat a.rb
require 'date'

class Date
   def self.last_day_of_the_month yyyy, mm
     d = new yyyy, mm
     d += 42                  # warp into the next month
     new(d.year, d.month) - 1 # back off one day from first of that month
   end
end

puts Date.last_day_of_the_month(2006, 9)
puts Date.last_day_of_the_month(2006, 12)
puts Date.last_day_of_the_month(2007, 2)


harp:~ > ruby a.rb
2006-09-30
2006-12-31
2007-02-28


-a
-- 
in order to be effective truth must penetrate like an arrow - and that is
likely to hurt. -- wei wu wei