Re: [Boost-users] Date calculations with exclusions

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-09-01 11:31:02

kingos_at_[hidden] wrote:
> Hi, 
> 
> I am hoping to use boost::date_time to do some date calculations. What I want to do is
> basically work out the number of days to a given date with various exclusions applied.
> 
> eg.
> 
> How many working days are there to christmas?
> 
> using namespace boost::gregorian;
> 
> int CalculateDaysToChristmas()
> {
> 	date_period someHoliday(date(2006, Dec, 01), date_duration(1));
> 
>     date today(2006, Sep, 1);
> 
>     date christmas(2006, Dec, 25);
> 
>     int days = 0;
>     for (day_iterator i = today; i != christmas; ++i)
>     {
>         if (is_weekday(*i) && !someHoliday.contains(*i))
>             ++days;
>     }
> 
>     return days;
> }
> 
> However, I can't find a simply way to work out is_weekday ...

Here's something I have laying around that does this:

using namespace boost::gregorian;
   inline
   bool is_weekday(date d)
   {
     greg_weekday dow = d.day_of_week();
     if (dow == Saturday || dow == Sunday) {
       return false;
     }
     return true;
   }

   inline
   int weekdays_in_period(const date_period& dp)
   {
     day_iterator i(dp.begin());
     int count = 0;
     while ( i <= dp.end()) {
       if (is_weekday(*i)) {
         count++;
       }
       ++i;
     }
     return count;
   }

When I'm writing this sort of code I also like to hide the details of getting 
the date period.  Something like this:

class holiday_period : public date_period
{
  public:
   holiday_period(const date& holiday_date) :
     date_period(day_clock::local_day(), holiday_date)
   {};
  private:
};

Now you can write:

    date christmas(2006, Dec, 25);
    hoiday_period hp(christmas);
    days days_until = weekdays_in_period(hp);

> Secondly, is there some way to put every sunday in as a date_period? 

Not sure what you have in mind here?

> Thirdly, this doesn't seem very optimal ... is there a better way of doing this?

No doubt, this is suboptimal.  A better way to do this is to figure out is to 
take advantage of the fact that a week is exactly 7 days and each week 
contains 5 non-weekend days (note that the weekend days aren't Sat/Sun in all 
parts of the world).  The tricky part is that you have to account for the 
boundary conditions of landing on a weekend, or starting on a weekend, less 
than one week, etc.  My guess is it would take an hour or two to really write 
it up and test all the cases.  Anyway, I've not had a real reason to ever 
write this one up.  Contributions always welcome ;-)

Jeff