Question

I have a class TContainer that is an aggregate of several stl collections pointers to TItems class.

I need to create an Iterator to traverse the elements in all the collections in my TContainer class abstracting the client of the inner workings.

What would be a good way to do this?. Should I crate a class that extends an iterator (if so, what iterator class should I extend), should I create an iterator class that is an aggregate of iterators?

I only need a FORWARD_ONLY iterator.

I.E, If this is my container:

typedef std::vector <TItem*> ItemVector;
class TContainer {
   std::vector <ItemVector *> m_Items;
};

What would be a good Iterator to traverse all the items contained in the vectors of the m_Items member variable.

Answer 1

When I did my own iterator (a while ago now) I inherited from std::iterator and specified the type as the first template parameter. Hope that helps.

For forward iterators user forward_iterator_tag rather than input_iterator_tag in the following code.

This class was originally taken from istream_iterator class (and modified for my own use so it may not resemble the istram_iterator any more).

template<typename T>
class <PLOP>_iterator
         :public std::iterator<std::input_iterator_tag,       // type of iterator
                               T,ptrdiff_t,const T*,const T&> // Info about iterator
{
    public:
        const T& operator*() const;
        const T* operator->() const;
        <PLOP>__iterator& operator++();
        <PLOP>__iterator operator++(int);
        bool equal(<PLOP>__iterator const& rhs) const;
};

template<typename T>
inline bool operator==(<PLOP>__iterator<T> const& lhs,<PLOP>__iterator<T> const& rhs)
{
    return lhs.equal(rhs);
}

Check this documentation on iterator tags:
http://www.sgi.com/tech/stl/iterator_tags.html

Having just re-read the information on iterators:
http://www.sgi.com/tech/stl/iterator_traits.html

This is the old way of doing things (iterator_tags) the more modern approach is to set up iterator_traits<> for your iterator to make it fully compatible with the STL.