Re: copy from keys from multimap into the vector

#include <vector>
#include <map>
#include <iterator>
#include <algorithm>
#include <iostream>

template<typename C, typename M>
class key_inserter :
  public std::iterator<std::output_iterator_tag,void,void,void,void> {
    private:
      C & d_coll;
    public:
      key_inserter(C & c) : d_coll(c) {}
      key_inserter & operator*() { return *this; }
      key_inserter & operator++() { return *this; }
      key_inserter & operator++(int) { return *this; }
      key_inserter &
      operator=(typename M::value_type const & p) {
        d_coll.push_back(p.first);
        return *this;
      }
};

template<typename C, typename M>
key_inserter<C,M> make_key_inserter(C & c, M & m) {
  return key_inserter<C,M>(c);
}

int main() {
  std::vector<int> v;
  std::map<int,int> m;
  m[0];m[1];m[2];m[6];
  std::copy(m.begin(),
            m.end(),
            make_key_inserter(v,m));
  std::copy(v.begin(),
            v.end(),
            std::ostream_iterator<int>(std::cout,"\n"));
  return 0;
}