std::unordered_multimap<Key,T,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_map>
 
void print_info(std::string_view rem, const std::unordered_multimap<int, char>& v)
{
    std::cout << rem << "{ ";
    for (const auto& [key, value] : v)
        std::cout << '[' << key << "]:" << value << ' ';
    std::cout << "}\n";
    std::cout << "Size=" << v.size() << '\n';
}
 
int main()
{
    std::unordered_multimap<int, char> container{{1, 'x'}, {2, 'y'}, {3, 'z'}};
    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