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::map<int, int>
contains any elements:
#include <map> #include <iostream> #include <utility> int main() { std::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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