The size() method of unordered_multiset is used to count the number of elements of unordered_set it is called with. It takes the number of elements in the container and counts the number of elements.
size_type size() const;
where size_type is an unsigned integral type.
Return Value: This function returns the length of the controlled sequence or in short, it returns the number of elements in the container.
Below program illustrate the unordered_multiset size() function :-
The container has 6 elements in it
It takes constant(O(1)) time of complexity to perform an operation.