std::unordered_set<Key,Hash,KeyEqual,Allocator>::clear
From cppreference.com
< cpp | container | unordered set
| void clear() noexcept; |
(since C++11) | |
Erases all elements from the container. After this call, size() returns zero.
Invalidates any references, pointers, or iterators referring to contained elements. May also invalidate past-the-end iterators.
Parameters
(none)
Return value
(none)
Complexity
Linear in the size of the container, i.e., the number of elements.
Example
Run this code
#include <algorithm> #include <iostream> #include <unordered_set> int main() { std::unordered_set<int> container{1, 2, 3}; auto print = [](const int& n) { std::cout << ' ' << n; }; std::cout << "Before clear:"; std::for_each(container.begin(), container.end(), print); std::cout << "\nSize=" << container.size() << '\n'; std::cout << "Clear\n"; container.clear(); std::cout << "After clear:"; std::for_each(container.begin(), container.end(), print); std::cout << "\nSize=" << container.size() << '\n'; }
Possible output:
Before clear: 1 2 3 Size=3 Clear After clear: Size=0
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior
|
|---|---|---|---|
| LWG 2550 | C++11 | for unordered associative containers, unclear if complexity is linear in the number of elements or buckets |
clarified that it's linear in the number of elements |
See also
| (C++11) |
erases elements (public member function) |