std:: erase_if (std::flat_map)

Erases all elements that satisfy the predicate pred from c .

The predicate pred is satisfied if the expression bool ( pred ( std:: pair < const Key & , const T & > ( e ) ) ) is true , where e is some element in c .

Key and T must be MoveAssignable . Otherwise, the behavior is undefined.

Parameters

Return value

The number of erased elements.

Complexity

Exactly c. size ( ) applications of the predicate pred .

Exceptions

If erase_if throws, c remains in valid but unspecified (maybe empty) state.

Notes

The algorithm is stable , that is, the order of elements that are not deleted remains unchanged.

Example

#include <iostream>
#include <flat_map>
 
void println(auto rem, auto const& container)
{
    std::cout << rem << '{';
    for (char sep[]{0, ' ', 0}; const auto& [key, value] : container)
        std::cout << sep << '{' << key << ", " << value << '}', *sep = ',';
    std::cout << "}\n";
}
 
int main()
{
    std::flat_map<int, char> data
    {
        {1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'},
        {5, 'e'}, {4, 'f'}, {5, 'g'}, {5, 'g'},
    };
    println("Original:\n", data);
 
    const auto count = std::erase_if(data, [](const auto& item)
    {
        auto const& [key, value] = item;
        return (key & 1) == 1;
    });
 
    println("Erase items with odd keys:\n", data);
    std::cout << count << " items removed.\n";
}

Original:
{{1, a}, {2, b}, {3, c}, {4, d}, {5, e}}
Erase items with odd keys:
{{2, b}, {4, d}}
3 items removed.

See also