std::map<Key,T,Compare,Allocator>::clear

void clear();

(noexcept since C++11)

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

Invalidates any references, pointers, and iterators referring to contained elements. Any past-the-end iterator remains valid.

Complexity

Linear in the size of the container, i.e., the number of elements.

Example

#include <iostream>
#include <string_view>
#include <map>

void print_info(std::string_view rem, const std::map<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::map<int, char> container{{1, 'x'}, {2, 'y'}, {3, 'z'}};
    print_info("Before clear: ", container);
    container.clear();
    print_info("After clear: ", container);
}

Output:

Before clear: { [1]:x [2]:y [3]:z }
Size=3
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 224	C++98	the complexity was `log(size()) + N`, but `N` was not defined	corrected to 'linear in `size()`'

std::map<Key,T,Compare,Allocator>::clear

Complexity

Example

Defect reports

See also