std::copy to std::cout for std::pair

Question

I have next code:

#include 
#include 
#include 

Answer 1

Here is an adaptor to use with std::copy and std::ostream_iterator for the std::pair type. You end up holding one extra reference, but the compiler optimization may take care of it. BTW, the first type in std::pair of the std::map::value_type will be a const.

template 
class pair_adaptor
{
public:
    const pair_type &m;
    pair_adaptor(const pair_type &a) : m(a) {}

    friend std::ostream &operator << (std::ostream &out, 
        const pair_adaptor  &d)
    {
        const pair_type &m = d.m;
        return out << m.first << " => " << m.second;
    }
};

typedef std::map::value_type value_type;

std::copy (mymap.begin(), mymap.end(),
    std::ostream_iterator < 
        pair_adaptor  > (std::cout, "\n"));

std::copy (mymap.begin(), mymap.end(),
    std::ostream_iterator < 
        pair_adaptor <
            std::pair>> (std::cout, "\n"));