std::unordered_set::empty

From cppreference.com

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_set<int> contains any elements:

#include <unordered_set>
#include <iostream>

int main()
{
    std::unordered_set<int> numbers;
    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(): 1
After adding elements, numbers.empty(): 0

See also

returns the number of elements
(public member function)