bool empty() const; | (until C++11) | |
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::list<int> contains any elements:
#include <list>
#include <iostream>
int main()
{
std::list<int> numbers;
std::cout << std::boolalpha;
std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';
numbers.push_back(42);
numbers.push_back(13317);
std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}Output:
Initially, numbers.empty(): true After adding elements, numbers.empty(): false
| returns the number of elements (public member function) |
|
|
(C++17) | checks whether the container is empty (function template) |
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