Re: [Boost-users] Iterator Range, sub range of a desired size

Subject: Re: [Boost-users] Iterator Range, sub range of a desired size
From: Bill Buklis (boostusr_at_[hidden])
Date: 2012-10-29 14:35:13

On 10/28/2012 11:40 PM, David Kimmel wrote:
> Is there a function in BOOST, given a starting point and a desired size, that
> returns iterators for a (sub) range?
>
> For example, given:
> a boost::circular_buffer which contains: 1 2 3 4 5 6 7 8 9 10
> a starting point which is an iterator pointing to 5
> and finally a desired size which is an int s = 4
>
> The result of which would be iterators producing: 5 6 7 8
>
> A possible implementation might be this (but I was hoping there was a BOOST
> version since I can't find an STD algorithm)
>
> template <typename Itr>
> std::pair<Itr, Itr> getWindowDown(Itr begin, Itr end, Itr start, const int
> windowSize)
> {
> 	// Down first, then up if need be
> 	const Itr bottom = (end - start > windowSize) ? (start + windowSize) :
> (end);
> 	const Itr top = (bottom - begin > windowSize) ? (bottom - windowSize) :
> (begin);
> 	return make_pair(top, bottom);
> }
>
>
> Thanks,
>

Would using next or advance work?

For example, something like:

range = std::make_pair(first, std::next(first, 4));

I can't remember offhand if next is only c++11. If so, there might be a 
boost::next available. Or alternatively use advance, but it'll require 
an extra variable to hold the end iterator.

Also, from a purely generic standpoint using std::distance is better 
than end - start.

-- 
Bill