Implementing Multidimensional Map in C++

Last Updated : 12 Jul, 2025

Multidimensional maps are used when we want to map a value to a combination of keys. The key can be of any data type, including those that are user-defined. Multidimensional maps are nested maps; that is, they map a key to another map, which itself stores combinations of key values with corresponding mapped values. Syntax:

// Creating a two-dimensional map:
map< key_1_type, map< key_2_type, value_type> > object;

// Creating an N-dimensional map:
map< key_1_type, map< key_2_type, ... map< key_N_type, value_type> > > object;

Example 1:

CPP14

// C++14 code to implement two-dimensional map

#include <bits/stdc++.h>
using namespace std;

int main()
{

    // Two-dimensional key
    map<int, map<int, int> > m;

    // For accessing outer map
    map<int, map<int, int> >::iterator itr;

    // For accessing inner map
    map<int, int>::iterator ptr;

    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            m[i][j] = i + j;
        }
    }

    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {

            // Accessing through array subscript
            cout << "First key is " << i
                 << " And second key is " << j
                 << " And value is " << m[i][j] << endl;
        }
    }

    cout << "\nNow accessing map though iterator \n\n";

    for (itr = m.begin(); itr != m.end(); itr++) {

        for (ptr = itr->second.begin(); ptr != itr->second.end(); ptr++) {
            cout << "First key is " << itr->first
                 << " And second key is " << ptr->first
                 << " And value is " << ptr->second << endl;
        }
    }
}

Output:

First key is 0 And second key is 0 And value is 0
First key is 0 And second key is 1 And value is 1
First key is 1 And second key is 0 And value is 1
First key is 1 And second key is 1 And value is 2

Now accessing map though iterator 

First key is 0 And second key is 0 And value is 0
First key is 0 And second key is 1 And value is 1
First key is 1 And second key is 0 And value is 1
First key is 1 And second key is 1 And value is 2

Example 2:

CPP14

// C++14 code to implement two-dimensional map
// and inserting value through insert()

#include <bits/stdc++.h>
using namespace std;

int main()
{

    // First key type is a string
    map<string, map<int, int> > m;

    map<string, map<int, int> >::iterator itr;
    map<int, int>::iterator ptr;

    m.insert(make_pair("Noob", map<int, int>()));
    m["Noob"].insert(make_pair(0, 5));

    m.insert(make_pair("Geek", map<int, int>()));
    m["Geek"].insert(make_pair(1, 10));

    m.insert(make_pair("Geek", map<int, int>()));
    m["Geek"].insert(make_pair(2, 20));

    for (itr = m.begin(); itr != m.end(); itr++) {

        for (ptr = itr->second.begin(); ptr != itr->second.end(); ptr++) {
            cout << "First key is " << itr->first
                 << " And second key is " << ptr->first
                 << " And value is " << ptr->second << endl;
        }
    }
}

Output:

First key is Geek And second key is 1 And value is 10
First key is Geek And second key is 2 And value is 20
First key is Noob And second key is 0 And value is 5