How to Check if a Map is Empty in C++?

In C++, a map is an associative container that stores elements as key-value pairs and an empty map means it contains no elements. In this article, we will learn how to check if a map is empty or not in C++.

Example:

Input: 
map<int,string>mp1 = {{1, "Ram"}, {2, "Mohit"}};
map<int,string> mp2={};

Output:
mp1 is not empty
mp2 is empty 

Check if a Map is Empty in C++

To check if a std::map is empty or not, we can use the std::map::empty() function that returns true if the map is empty otherwise it returns false.

C++ Program to Check if a Map is Empty or Not

The below example demonstrates how we can use the empty() function to check if the given map is empty or not in C++ STL.

C++

// C++ program to check whether map is empty or not.

#include <iostream>
#include <map>
using namespace std;

int main()
{

    // defining an empty map
    map<int, string> mp1;

    // checking if the mp1 is empty
    if (mp1.empty()) {
        cout << "mp1 is empty." << endl;
    }
    else {
        cout << "mp1 is not empty." << endl;
    }

    // defining a map and inserting a key value pair
    map<int, string> mp2;
    mp2.insert(make_pair(1, "One"));

    // Checking if mp2 is empty
    if (mp2.empty()) {
        cout << "mp2 is empty." << endl;
    }
    else {
        cout << "mp2 is not empty." << endl;
    }

    return 0;
}

Output

mp1 is empty.
mp2 is not empty.

Time Complexity: O(1)
Auxiliary Space: O(1)

Note: We can also use map::size() function to check if the given map is empty or not in C++.