#include <map>
    #include <vector>
    #include <iostream>

    using namespace std;

    int main()
    {
        vector<int> keys = {0, 1};

        map<int, int> m;
        m[1] = 5;
        m[2] = 12;

        for (const int i : keys)
        {
            m[i]; // touch value
        }

        for (auto const & kv : m)
        {
            cout << kv.first << ", " << kv.second << endl;
        }
    }