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

Subject: Re: [Boost-users] Iterator Range, sub range of a desired size
From: David Kimmel (davidwkimmel_at_[hidden])
Date: 2012-10-30 17:30:49

Nice, that pretty much does it.  Still had to add another range to make
sure the final range contained the proper size requested (see r2)

auto r = boost::make_iterator_range(
      boost::next(boost::begin(v), start - 1),
      boost::next(boost::begin(v), std::min(start - 1 + window,
             static_cast<int>(boost::distance(v))))
 );

auto r2 = boost::make_iterator_range(
boost::prior(r.end(), std::min( static_cast<int>(r.end()-source.begin()),
window)),
r.end());

Now range r2 should have window number of elements as long as source has at
least window number of elements.

Finally, sounds like there is an issue with using distance for non random
access containers or an input range but that should not be a problem in my
case.

On Tue, Oct 30, 2012 at 11:05 AM, Neil Groves <neil_at_[hidden]>wrote:

> On Tue, Oct 30, 2012 at 4:50 PM, David Kimmel <davidwkimmel_at_[hidden]>wrote:
>
>> I tried it out, yes you can get make_iterator_range with next to work.  I
>> like boost::next but for what I wanted it does not seem to work
>> appropriately.  Your example of "make_iterator_range(boost::next(b.begin,
>> wSize), v.end())" will only skip the first "wSize" elements.  What I want
>> is a range that contains at most wSize elements (if possible) - taking them
>> from after (and containing) a start index.
>>
>>
> boost::next absolutely shouldn't be checking against end(), that would not
> be obeying the zero-overhead principle. For your requirements surely you
> just alter the parameters to make_iterator_range?
>
>
>> Even my second attempt with this approach (commented out lines) does not
>> work because next does not check to see if it is past end.  Perhaps if
>> there is a "min" method I could pass the "boost::next(v.begin() +
>> (start-1), window)" and "v.end()".
>>
>>
> std::min from <algorithm> ?
>
>
>>  typedef vector<int> Vector;
>> Vector v = { 1, 2, 3, 4, 5, 6, 7, 8 , 9, 10, 11 };
>>
>> const int start = 10;
>>  const int window = 4;
>>
>> auto r = boost::make_iterator_range(boost::next(v.begin(), start-1),
>> v.end());
>>  auto r2 = boost::make_iterator_range(boost::prior(r.end(), window),
>> r.end());
>>
>> // auto r = boost::make_iterator_range(v.begin() + (start-1),
>> boost::next(v.begin() + (start-1), window) );
>> // auto r2 = boost::make_iterator_range(boost::prior(r.end(), window),
>> r.end());
>>
>>
>
> // General solution for all iterator types - assume that source here is v
> from your example
> auto r = boost::make_iterator_range(
>     boost::next(boost::begin(source), start - 1),
>     boost::next(boost::begin(source), std::min(start - 1 + window,
> static_cast<int>(boost::distance(source))))
> );
>
> I'm not seeing a problem. Am I misunderstanding your question?
>
> Neil Groves
>
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