std::unordered_set<Key,Hash,KeyEqual,Allocator>::clear

From cppreference.com

 
 
 
 
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

#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)