Re: Multimap: how to get a key list?
Michael Doubez <michael.doubez@free.fr> wrote:
On 2 mar, 14:38, "Daniel T." <danie...@earthlink.net> wrote:
Michael Doubez <michael.dou...@free.fr> wrote:
Another solution is to use decoration:
template<typename iterator_type>
class key_iterator:
? ?std::iterator< typename iterator_type::iterator_category
? ? ? ? ? ? ? ? // return type of iterator is key type
? ? ? ? ? ? ? ? , typename iterator_type::value_type::first_type
? ? ? ? ? ? ? ? , typename iterator_type::difference_type
{
? public:
? ? // put here the typedefs iterator_category, ?...
? ? // build from
? ? key_iterator(const iterator_type& i):it(i){}
? ? // usual operation on iterator
? ? key_iterator& operator++()
? ? { ++it;return *this;}
? ? view_iterator ?operator++(int)
? ? { return key_iterator(it++);}
? ? bool ? ?operator ?== (const key_iterator& rhs) const
? ? {return it == rhs.it;}
? ? // and so on for other iterator operations
? ? // return key
? ? reference operator*() const
? ? {return it->first; }
? ? pointer operator->() const
? ? {return &it->first; }
? private:
? ? ?iterator_type it;
};
And then you can use
template<class T>
key_iterator<typename T::iterator_type> key_begin(T& container)
{
?return container.begin();
}
template<class T>
key_iterator<typename T::iterator_type> key_end(T& container)
{
?return container.end();
}
You can do whatever you want on the keys of an associative container.
std::accumulate(key_begin(aMap),key_end(aMap), 0 );
I think part of the point of the exorcise was to remove duplicate keys
from the multimap.
std::unique_copy() with the decorated iterator does the trick.
I like this idea better than the ones I came up with. OK if I use it?
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