W3cubDocs

/C++

std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::empty

bool empty() const noexcept;
(since C++11)
(until C++20)
[[nodiscard]] bool empty() const noexcept;
(since C++20)

Checks if the container has no elements, i.e. whether begin() == end().

Parameters

(none).

Return value

true if the container is empty, false otherwise.

Complexity

Constant.

Example

The following code uses empty to check if a std::unordered_multiset<int> contains any elements:

#include <unordered_set>
#include <iostream>
 
int main()
{
    std::unordered_multiset<int> numbers;
    std::cout << std::boolalpha;
    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
 
    numbers.insert(42);
    numbers.insert(13317); 
    std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}

Output:

Initially, numbers.empty(): true
After adding elements, numbers.empty(): false

See also

(C++11)
returns the number of elements
(public member function)
(C++17)
checks whether the container is empty
(function template)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/container/unordered_multiset/empty