unordered_set size() function in C++ STL

The unordered_set::size() method is a builtin function in C++ STL which is used to return the number of elements in the unordered_set container. Syntax:

unordered_set_name.size()

Parameter: It does not accepts any parameter. Return Value: The function returns the number of elements in the container. Below programs illustrate the unordered_set::size() function: Program 1: 

CPP

// C++ program to illustrate the
// unordered_set.size() function
#include <iostream>
#include <unordered_set>

using namespace std;

int main()
{

    unordered_set<int> arr1 = { 1, 2, 3, 4, 5 };

    // prints the size of arr1
    cout << "size of arr1:" << arr1.size();

    // prints the element
    cout << "\nThe elements are: ";
    for (auto it = arr1.begin(); it != arr1.end(); it++)
        cout << *it << " ";

    return 0;
}

Output:

size of arr1:5
The elements are: 5 1 2 3 4

Program 2: 

CPP

// C++ program to illustrate the
// unordered_set::size() function
// when container is empty
#include <iostream>
#include <unordered_set>

using namespace std;

int main()
{

    unordered_set<int> arr2 = {};

    // prints the size
    cout << "Size of arr2 : " << arr2.size();

    return 0;
}

Output:

Size of arr2 : 0

Time complexity: O(1)