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().
(none).
true if the container is empty, false otherwise.
Constant.
The following code uses empty to check if a std::unordered_map<int,int> contains any elements:
#include <unordered_map>
#include <iostream>
#include <utility>
int main()
{
std::unordered_map<int, int> numbers;
std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
numbers.emplace(42, 13);
numbers.insert(std::make_pair(13317, 123));
std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}Output:
Initially, numbers.empty(): 1 After adding elements, numbers.empty(): 0
| returns the number of elements (public member function) |
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