What is a multiset in C++ STL?

A multiset in STL is an associative container just like a set the only difference is it can store duplicate elements in it.

Syntax:

multiset<object_type> variable_name;

Example:

multiset<int> s;
multiset<string> str;

Functions in multiset:

• insert() – to insert an element in the multiset.

multiset<int> s;
s.insert(1);
s.insert(2);

• begin() – return an iterator pointing to the first element in the multiset.

s.begin();

• end() – returns an iterator to the theoretical element after the last element.

s.end();

• count() – gives the count of a particular element in the multiset.

multiset<int> s;
s.insert(1);
s.insert(2);
s.count(2); //returns 1

• clear() – deletes all the elements in the multiset.

s.clear();

• find() – to search an element in the multiset.

multiset<int> s;
s.insert(1);
s.insert(2);
if(s.find(2)!=s.end())
cout<<"true"<<endl;

• erase() – to delete a single element or elements between a particular range.

s.erase();

• size() – returns the size of the multiset.

s.size();

• empty() – to check if the multiset is empty or not.

s.empty();

Code:

#include<bits/stdc++.h>

using namespace std;

int main() {
  multiset < int > s;
  for (int i = 1; i <= 10; i++) {
    s.insert(i);
  }
  s.insert(5);
  cout << "Elements present in the multiset: ";
  for (auto it = s.begin(); it != s.end(); it++) {
    cout << * it << " ";
  }
  cout << endl;
  int n = 2;
  if (s.find(2) != s.end())
    cout << n << " is present in multiset" << endl;

  s.erase(s.begin());
  cout << "Elements after deleting the first element: ";
  for (auto it = s.begin(); it != s.end(); it++) {
    cout << * it << " ";
  }
  cout << endl;

  cout << "The size of the multiset is: " << s.size() << endl;

  if (s.empty() == false)
    cout << "The multiset is not empty " << endl;
  else
    cout << "The multiset is empty" << endl;
  s.clear();
  cout << "Size of the multiset after clearing all the elements: " << s.size();
}

• cbegin() – it refers to the first element of the multiset.
• cend() – it refers to the theoretical element after the last element of the multiset.
• rbegin() – it points to the last element of the multiset.
• rend() – it points to the theoretical element before the first element of the multiset.
• emplace() – to insert an element in the multiset.
• max_size() – the maximum elements a multiset can hold.

Special thanks to Subhrajit Das for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article