RE: [Boost-Users] Date_Time library question...

From: Jeff Garland (jeff_at_[hidden])
Date: 2002-11-29 06:54:34

Hi Luc - 

> I was wondering, while looking at the source files, why the 
> date_iterator doesn't provide an operator--() ???

A couple reasons.
1) I wasn't sure it would be needed, so to keep things simple I
   left it out.
2) See below...

> I've added this in the "date_iterator.hpp" file :
> 
> //---------------------------------------------------------
>     date_itr_base& operator--()
>     {
>       current_ = current_ - get_offset(current_);
>       return *this;
>     }
> //---------------------------------------------------------
> 
> I've rebuilt the library and done this little test :
> 
> //---------------------------------------------------------
> #include <iostream>
> #include <boost/date_time/gregorian/gregorian.hpp>
> 
> int main(void)
> {
>    using namespace boost::gregorian;
> 
>    date today = day_clock::local_day();
>    day_iterator ditr(today, 1);
>    int nbDaysToIterate = 360;
> 
>    for (;nbDaysToIterate != 0; --ditr, --nbDaysToIterate)
>    {
>       std::cout << to_iso_extended_string(*ditr) << std::endl;
>    }
> }
> //---------------------------------------------------------
> 
> Everything seems to run OK. I've checked the february month and it has a 
> 28th... Now I wonder why wasn't it included in the release ???

It's true that this works fine for the day_iterator.  If you try the
same test with the month and year iterators, they will fail.  The reason
being that the functors that calculate 'add a month' and 'add a year' 
are written assuming a forward iterator.  That's not to say that they
couldn't be modified to support bi-directional iteration, just that
it is a tad harder in these cases.

Jeff