Create & Initialise MultiSet in C++

In this tutorial, we will discuss how to create & initialise a multiset in C++.

To use multiset, you need to include the ‘set’ header file i.e.

#include <set>

The syntax for creating a multiset object is as follows:

std::multiset<data_type> obj;

We need to specify the data type (data_type) as a template parameter when declaring a multiset object. This means that this multiset can only hold elements of the specified data type.

For instance, one could create a multiset of integers, like this,

std::multiset<int> numbers;

or a multiset of strings, like this,

std::multiset<std::string> words;

This will establish an empty multiset of strings; there will be no elements in it.

You can also create and initialize a multiset in the same line. Like this,

// Create multiset and initialize with values
std::multiset<int> numSet {11, 22, 33, 33, 33, 44, 33, 55};

For example, doing so with integers will initialize the multiset with 8 integer values. Internally, the multiset arranges the elements in a sorted order, which is ascending by default. We can verify this by iterating over all the elements in the multiset using a range-based for loop. In the example below, we’ll create a multiset of integers, initialize it using an initializer list, and then iterate over all the elements of the multiset, printing them to the console.

Let’s see the complete example,

#include <iostream>
#include <set>

int main()
{
    // Create an empty multiset
    std::multiset<int> numbers;

    // Create multiset and initialize with values
    std::multiset<int> numSet {11, 22, 33, 33, 33, 44, 33, 55};

    // Content of the multiset will be:
    // 11, 22, 33, 33, 33, 33, 44, 55

    // Iterate over set and print elements
    for(const auto& elem : numSet)
    {
        std::cout<< elem<< ", ";
    }
    std::cout<<std::endl;
}

Output

11, 22, 33, 33, 33, 33, 44, 55,

Summary

Today, we learned how to how to create & initialise a multiset in C++.