std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::clear
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std::unordered_multimap unordered_multimap::clear
(C++23)
(C++17)
(C++17)
(C++20)
(until C++20)
void clear() noexcept;
(since C++11) (constexpr since C++26)
Erases all elements from the container. After this call, size() returns zero.
Invalidates any references, pointers, and iterators referring to contained elements. May also invalidate past-the-end iterators.
Contents
[edit] Complexity
Linear in the size of the container, i.e., the number of elements.
[edit] Example
Run this code
#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); }
Possible output:
Before clear: { [1]:x [2]:y [3]:z }
Size=3
After clear: { }
Size=0Defect 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 |