std::erase_if (std::flat_map)

< cpp‎ | container‎ | flat map
Defined in header <flat_map>
template< class Key, class T, class Compare, class KeyContainer, class MappedContainer,

          class Pred >
std::flat_map<Key, T, Compare, KeyContainer, MappedContainer>::size_type
    erase_if( std::flat_map<Key, T, Compare, KeyContainer, MappedContainer>& c,

              Pred pred );
(since C++23)

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.


[edit] Parameters

c - container adaptor from which to erase
pred - predicate that returns true if the element should be erased

[edit] Return value

The number of erased elements.

[edit] Complexity

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


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


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

[edit] Example

#include <iostream>
#include <flat_map>
void print(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'},
    print("Original:\n", data);
    const auto count = std::erase_if(data, [](const auto& item)
        auto const& [key, value] = item;
        return (key & 1) == 1;
    print("Erase items with odd keys:\n", data);
    std::cout << count << " items removed.\n";


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

[edit] See also

removes elements satisfying specific criteria
(function template) [edit]