Re: copy from keys from multimap into the vector

You could use std::transform with std::back_inserter to load vector
and a functor to extract the std::string from multimap's value_type.

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

template< typename P >
struct extract_first
{
  const typename P::first_type&
  operator()(const P& p) const
  {
    return p.first;
  }
};

int main()
{
  std::vector< std::string > vec;
  std::multimap< std::string, int > mm;
  // populate mm

  typedef std::multimap< std::string, int >::value_type VType;

  std::transform( mm.begin(),
                  mm.end(),
                  std::back_inserter(vec),
                  extract_first< VType >() );
}