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

Since C++11

Erases all elements from the container. After this call, size() returns zero.

# Declarations

void clear() noexcept;

(since C++11)

# Return value

(none)

# Example

#include <iostream>
#include <string_view>
#include <unordered_set>
 
void print_info(std::string_view rem, const std::unordered_set<int>& v)
{
    std::cout << rem << "{ ";
    for (const auto& value : v)
        std::cout << value << ' ';
    std::cout << "}\n";
    std::cout << "Size=" << v.size() << '\n';
}
 
int main()
{
    std::unordered_set<int> container{1, 2, 3};
    print_info("Before clear: ", container);
    container.clear();
    print_info("After clear: ", container);
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 2550	C++11	for unordered associative containers, unclear if complexityis linear in the number of elements or buckets	clarified that it’s linear in the number of elements

# See also

erase