c++ map access by key code example

Example 1: c++ get map keys

template<typename TK, typename TV>
std::vector<TK> extract_keys(std::map<TK, TV> const& input_map) {
  std::vector<TK> retval;
  for (auto const& element : input_map) {
    retval.push_back(element.first);
  }
  return retval;
}

Example 2: map data access by key in cpp

// accessing mapped values
#include <iostream>
#include <map>
#include <string>

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

  mymap['a']="an element";
  mymap['b']="another element";
  mymap['c']=mymap['b'];

  std::cout << "mymap['a'] is " << mymap['a'] << '\n';
  std::cout << "mymap['b'] is " << mymap['b'] << '\n';
  std::cout << "mymap['c'] is " << mymap['c'] << '\n';
  std::cout << "mymap['d'] is " << mymap['d'] << '\n';

  std::cout << "mymap now contains " << mymap.size() << " elements.\n";

  return 0;
}