Flatten an std::map into an std::vector

flatten.cc

// g++ -O3 -I/opt/local/include -L/opt/local/lib -lboost_system flatten.cc
#include <iostream>
#include <algorithm>

#include <map>
#include <vector>
#include <string>

#include <boost/bind.hpp>
#include <boost/bind/placeholders.hpp>

namespace {
/*static*/ void print(const std::string& elem)
{
    std::cout << elem << std::endl;
}
}

template <typename K, typename V>
std::size_t flatten(std::map<K,V>& m, std::vector<V>& v)
{
    v.clear();
    v.reserve(m.size());
    std::transform(m.begin(), m.end(),
                   std::back_inserter(v),
                   boost::bind(&std::map<K,V>::value_type::second, _1));
    return v.size();
}

int main(int argc, char* argv[])
{
    std::map<int, std::string> m;
    std::vector<std::string> v;

    m[1] = "World";
    m[0] = "Hello";
    m[2] = "!!";

    flatten(m,v);

    std::for_each(v.begin(), v.end(), print);

    return 0;
}