NAME¶

std::unordered_set::empty - std::unordered_set::empty

Synopsis¶

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:

// Run this code

#include <iostream>
#include <unordered_set>

int main()
{
std::unordered_set<int> numbers;
std::cout << std::boolalpha;
std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';

numbers.insert(42);
numbers.insert(19937);
std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}

Output:¶

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

See also¶

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