multimap clear() function in C++ STL

The multimap clear() function is an inbuilt function in C++ STL which is used to remove all elements from the multimap container (which are destroyed), leaving the container with a size of 0.

Syntax :

mymultimap_name.clear()

Parameters: This function does not take any arguments.

Return Value: This function does not returns anything. The return type of the function is void. It just empties the whole container.

Below program illustrate the multimap::clear() function in C++: 

C++

// CPP program to illustrate the
// multimap::clear() function

#include <cstring>
#include <iostream>
#include <map>

using namespace std;

int main()
{
    // Creating multimap of string and int
    multimap<string, int> mymultimap;

    // Inserting 3 Items with their value
    // using insert function
    mymultimap.insert(pair<string, int>("Item1", 10));
    mymultimap.insert(pair<string, int>("Item2", 20));
    mymultimap.insert(pair<string, int>("Item3", 30));

    cout << "Size of the multimap before using "
         << "clear function : ";
    cout << mymultimap.size() << '\n';

    // Removing all the elements
    // present in the multimap
    mymultimap.clear();

    cout << "Size of the multimap after using"
         << " clear function : ";
    cout << mymultimap.size() << '\n';

    return 0;
}

Output

Size of the multimap before using clear function : 3
Size of the multimap after using clear function : 0

Time Complexity: O(N), where N is the total number of elements in multimap.