unordered_set empty() function in C++ STL

The unordered_set::empty is a built-in function in C++ STL which is used to check if an unordered_set container is empty or not. It returns True if the unordered_set container is empty, otherwise it returns False. 

Syntax:

map_name.empty()

Parameters: This function does not accepts any parameter. 

Return Value: It returns a boolean value True if the unordered_set container is empty, else false. 

Below programs illustrate the above function: 

Program 1:

CPP

// C++ program to illustrate the
// unordered_set::empty function
#include <iostream>
#include <unordered_set>
using namespace std;

int main()
{

    // declaration
    unordered_set<int> sample;

    // Check whether the unordered_set is empty
    if (sample.empty() == true)
        cout << "true" << endl;
    else
        cout << "false" << endl;

    // Insert a value
    sample.insert(5);

    // Now check whether it is empty
    if (sample.empty() == true)
        cout << "true" << endl;
    else
        cout << "false" << endl;

    return 0;
}

Output:

true
false

Program 2:

CPP

// C++ program to illustrate the
// unordered_set::empty function
#include <iostream>
#include <unordered_set>
using namespace std;

int main()
{
    // declaration
    unordered_set<int> uset;

    // Insert a value
    uset.insert({ 5, 6, 7, 8 });
    // Check whether the unordered_set is empty
    if (uset.empty() == true)
        cout << "true" << endl;
    else
        cout << "false" << endl;

    return 0;
}

Output:

false

Time complexity: O(1)