Re: AW: date arithmetic?

[Rici Lake <lua@...>]

On 23-Aug-05, at 5:09 PM, steffenj wrote:

> Seems to work, but I'm not sure if this is by luck or design.. :)

I think it's by luck. The "official" way of doing it would be to figure 
out how much was a day by subtracting one valid date from the next 
valid date (although it would work out to 24*60*60 on most OS's), and 
then subtracting that from the first day of the next month to get the 
last day of the current month.

However, if your way works on all the OS's you care about, go for it :)

Sample code:

do
  local oneDay = os.time{year = 2004, month = 2, day = 2}
                 - os.time{year = 2004, month = 2, day = 1}
  function lastDayOfMonth(aDate)
    local nextMonth = {year = aDate.year, month = aDate.month + 1, day 
= 1}
    if nextMonth.month > 12 then
      nextMonth.year, nextMonth.month = nextMonth.year + 1, 1
    end
    return os.date("*t", os.time(nextMonth) - oneDay)
  end
end