multiset clear() function in C++ STL

Last Updated : 30 Nov, 2021

The multiset::clear() function is a built-in function in C++ STL which removes all elements from the multiset container. The final size of multiset container after removal is 0.

Syntax:

multiset_name.clear()

Parameters: The function does not accept any parameter.
Return Value: The function does not returns anything.

Below programs illustrates the multiset::clear() function:

Program 1:

C++

// C++ program to demonstrate the
// multiset::clear() function
#include <bits/stdc++.h>
using namespace std;
int main()
{

    int arr[] = { 15, 10, 15, 11, 10 };

    // initializes the set from an array
    multiset<int> s(arr, arr + 5);

    // prints all elements in set
    cout << "The elements in multiset are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";

    cout << "\nThe size after clear() is: ";

    // erases all elements
    s.clear();
    cout << s.size();

    return 0;
}

Output:

The elements in multiset are: 10 10 11 15 15 
The size after clear() is: 0

Time Complexity: O(N), where N is the total number of elements present in the multiset.
Auxiliary Space: O(N)

Program 2:

C++

// C++ program to demonstrate the
// multiset::clear() function
#include <bits/stdc++.h>
using namespace std;
int main()
{

    int arr[] = { 15, 10, 15, 11, 10, 18, 18, 20, 20 };

    // initializes the set from an array
    multiset<int> s(arr, arr + 9);

    // prints all elements in set
    cout << "The elements in multiset are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";

    cout << "\nThe size after clear() is: ";

    // erases all elements
    s.clear();
    cout << s.size();

    return 0;
}

Output:

The elements in multiset are: 10 10 11 15 15 18 18 20 20 
The size after clear() is: 0

Time Complexity: O(N), where N is the total number of elements present in the multiset.
Auxiliary Space: O(N)

multiset::swap() in C++ STL

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