Re: Accessing Portion(s) of STL Container

From:

"Daniel T." <daniel_t@earthlink.net>

Newsgroups:

comp.lang.c++

Date:

Sat, 30 Oct 2010 10:58:30 -0400

Message-ID:

<daniel_t-3EBD1C.10583030102010@70-3-168-216.pools.spcsdns.net>

mrc2323@cox.net (Mike Copeland) wrote:

Is there a way to access a "chunk" (or portion) of an STL map? That
is, I have a map declared, and it will normally contain more than, say,
25 objects. I want to display 25 objects at a time, e.g. 1-25, 26-50,
etc. Of course, I don't expect to have multiples of 25 to work with, so
I want to know when the what's in the last "page" of display data.
Please advise. TIA

As long as you are not adding to, or removing from the map, you could
simply iterate through it 25 elements at a time.

That's the case with my data, but _how_ do I access, say, objects 26-
50 without "picking" that range as I iterate through the entire data
set?

You have to iterate through the data set, that can't be helped.
Fortunately, that isn't a big deal.

// untested code, but it should give you the idea.
   template < typename FwIt >
std::pair<FwIt, FwIt> subrange(FwIt begin, FwIt end,
                                                int start, int size) {
   std::pair<FwIt, FwIt> result = make_pair(begin, end);
   while (result.first != end && start) {
      ++result.first;
      --start;
   }
   result.second = result.first;
   while (result.second != end && size) {
      ++result.second;
      --size;
   }
   return result;
}