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

In C++, a set is an associative container that stores unique elements in a sorted order. In this article, we’ll explore different approaches to check if a set is empty in C++ STL.

Check if a Set is Empty or Not in C++

To check if a std::set is empty in C++, we can use the std::set::empty() function. This function returns a boolean value indicating whether the set is empty.

C++ Program to Check if a Set is Empty

C++

// C++ Program to show how to check if a set is empty or not
#include <iostream>
#include <set>
using namespace std;

int main()
{
    // Creating sets named 'mySet1' and 'mySet2'
    set<int> mySet1;
    set<int> mySet2 = { 1, 2 };

    // Checking if mySet1 is empty
    if (mySet1.empty()) {
        cout << "Set1 is empty." << endl;
    }
    else {
        cout << "Set1 is not empty." << endl;
    }

    // Checking if mySet1 is empty
    if (mySet2.empty()) {
        cout << "Set2 is empty." << endl;
    }
    else {
        cout << "Set2 is not empty." << endl;
    }

    return 0;
}

// This code is contributed by Susobhan Akhuli

Output

Set1 is empty.
Set2 is not empty.

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

The set container in C++ STL provides an size() member function that returns the size (or number of elements) of the set. We can also check is a set is empty or not using size() function in C++ because if the size is 0, then the set is empty otherwise not.