std::unordered_map clear() method

od C++11

// Non const version only
void clear() noexcept;

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

Invalidation

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 - O(size()).

Exceptions

(none)

Example

Main.cpp

#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