Generic Map to String Map (convert_to_string_map) c++

convert_to_string_map.cpp

#include <stdio.h>
#include <stdlib.h>
#include <map>
#include <functional>
#include <string> 
#include <iostream> 

template <typename T1, typename T2>
static std::map<std::string, std::string> convert_to_string_map(std::map<T1, T2> _map_in,
        std::function<std::pair<std::string, std::string>(T1, T2) > converter) {
    std::map<std::string, std::string> retval;
    for (auto _map_it : _map_in) {
        auto _values = converter(_map_it.first, _map_it.second);
        retval[_values.first] = _values.second;
    }
    return retval;
}

std::pair<std::string, std::string> testFunct(char a, int b) {
    std::pair<std::string, std::string> retval;
    retval.first = std::to_string(a);
    retval.second = std::to_string(b);
    return retval;
}

int main() {
    std::map<char, int> first;

    first['a'] = 10;
    first['b'] = 30;
    first['c'] = 50;
    first['d'] = 70;

    std::map<std::string, std::string> newMap;
    std::function < std::pair<std::string, std::string>(char, int) > myFunc = testFunct;
    newMap = convert_to_string_map(first, myFunc);

    std::cout << "Old Map:\n";
    for (auto _map_it : first) {
        printf("%c -> %d\n", _map_it.first, _map_it.second);
    }

    std::cout << "\nNew map:\n";
    for (auto _map_it : newMap) {
        printf("%s -> %s\n", _map_it.first.c_str(), _map_it.second.c_str());
    }
}