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

Question

I have next code:

#include 
#include 
#include 

Answer 1

There is no standard way to cout a std::pair because, well, how you want it printed is probably different from the way the next guy wants it. This is a good use case for a custom functor or a lambda function. You can then pass that as an argument to std::for_each to do the work.

typedef std::map MyMap;

template 
struct PrintMyMap : public std::unary_function
{
    std::ostream& os;
    PrintMyMap(std::ostream& strm) : os(strm) {}

    void operator()(const T& elem) const
    {
        os << elem.first << ", " << elem.second << "\n";
    }
}

To call this functor from your code:

std::for_each(some_map.begin(),
              some_map.end(),
              PrintMyMap(std::cout));