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Showing content from https://en.cppreference.com/w/cpp/language/../language/../algorithm/../container/map/clear.html below:

std::map<Key,T,Compare,Allocator>::clear - cppreference.com

void clear();

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.

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

#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

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

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