table of contents
std::unordered_map::clear(3) | C++ Standard Libary | std::unordered_map::clear(3) |
NAME¶
std::unordered_map::clear - std::unordered_map::clear
Synopsis¶
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
for unordered associative
LWG 2550 C++11 containers, unclear if complexity clarified that it's linear
in
is linear in the number of the number of elements
elements or buckets
See also¶
erase erases elements
(C++11) (public member function)
2022.07.31 | http://cppreference.com |