std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::clear
From cppreference.com
< cpp | container | unordered map
| 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_map> int main() { std::unordered_map<int, char> container{{1, 'x'}, {2, 'y'}, {3, 'z'}}; auto print = [](std::pair<const int, char>& n) { std::cout << " " << n.first << '(' << n.second << ')'; }; 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(x) 2(y) 3(z) 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) |