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From: Michael Doubez on 11 Mar 2010 04:32
On 10 mar, 20:15, "Hicham Mouline" <hic...(a)mouline.org> wrote:
> I have in input an STL container say std::vector<T> or std::list<T> called
> my_container;
>
> Is there any advised style re filtering such a container, so that following
> code can work only on a subset of that container , without knowing that it
> has been filtered?
>
> Say the initial container has 100 elements sorted according to some
> criteria, and the filter tells us to work only on the 20 elements.
>
> The filter could return to us a begin iterator and an end iterator to those
> 20 elements only.
> Subsequent code would then use only the iterators, and not functions like
> my_container.front()
> or
> my_container.size()
>
> Is this a customary way? Or is there something that returns a view on the
> original container?

By filtering, I assume you are talking about a subrange of the
container.

It shouldn't be too hard to make a container that uses a range as its
content:

template <class TIteraror>
class range_container
{
public:
// container types
typedef typename std::iterator_traits<TIteraror>::value_type
value_type;
typedef TIteraror iterator;
typedef std::const_iterator<TIteraror> iterator;
typedef typename std::iterator_traits<TIteraror>::reference
reference;
typedef const value_type& const_reference;
typedef typename std::iterator_traits<TIteraror>::pointer
pointer;
typedef typename std::iterator_traits<TIteraror>::difference_type
difference_type;
typedef typename std::iterator_traits<TIteraror>::size_type
size_type;

// constructor
range_container(iterator begin_range, iterator end_range)
: _begin(begin_range)
, _end (end_range)
{}
// do the same for copy constructor operator and swap

iterator begin(){ return _begin;}
iterator end(){ return _end; }
// same for const flavor

bool empty()const { return _begin == _end }

size_type size()const { return std::distance(_begin,_end);}

private:
iterator _begin;
iterator _end;
};

Depending on the kind of iterator, you can even provide an augmented
interface (reverse_iterator ...).

--
Michael


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