Exiv2

    /* Wraps a map iterator, returning the value on dereference */

    template<typename _Container, typename _Iterator, typename _ValueType = typename _Iterator::value_type::second_type>

    class map_value_iterator

        : public std::iterator<typename _Iterator::iterator_category, _ValueType, typename _Iterator::difference_type>

    {

    private:

        /*

         * const_map_value_iterator should look like an iterator of

         * const _ValueType.  Unfortunately, the map const_iterator

         * is actually just an iterator of const pairs, where

         * _ValueType is not const, so we need to explicitly add

         * const to _ValueType.

         */

        typedef map_value_iterator<_Container, typename _Container::const_iterator, const typename _Container::const_iterator::value_type::second_type> const_map_value_iterator;

    public:

        _Iterator it;

        map_value_iterator() {}

        map_value_iterator(typename _Container::const_iterator it) : it(it) {}

        map_value_iterator(typename _Container::iterator it) : it(it) {}

        _ValueType& operator*() const { return it->second; }

        _ValueType* operator->() const { return &it->second; }

        map_value_iterator& operator++() { it++; return *this; }

        map_value_iterator& operator++(int) { it++; return *this; }

        map_value_iterator& operator--() { it--; return *this; }

        map_value_iterator& operator--(int) { it--; return *this; }

        bool operator==(map_value_iterator const & rhs) const { return it == rhs.it; }

        bool operator!=(map_value_iterator const & rhs) const { return it != rhs.it; }

        /* Support conversion to const_iterator */

        operator const_map_value_iterator() const

        {

            return const_map_value_iterator(it);

        }

    };