C++ map<int, map<int, int>>

mapOfMap.hpp

// C++17 for structure binding
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <map>

using namespace std;

int main()
{
    map<int, map<int,int>> mapmap = {};
    
    mapmap[1][2] = 3;
    mapmap[1][3] = 30;
    mapmap[0][0] = 0;
    
    for(auto& [k, v]: mapmap[1])
        cout << "mapmap[1]:" << k << " " << v << endl;
    cout << endl;
    
    for(auto& [k, v]: mapmap[500])
        cout << "mapmap[500]:" << k << " " << v << endl;
    cout << "size of 500: " << mapmap[500].size() << endl;
    cout << endl;
}