NAME¶

std::erase_if(std::flat_map) - std::erase_if(std::flat_map)

Synopsis¶

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, (since C++23)
MappedContainer>::size_type
erase_if( std::flat_map<Key, T, Compare, KeyContainer,
MappedContainer>& c,

Pred pred );

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¶

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

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¶

// Run this code

#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";
}

Output:¶

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¶

remove removes elements satisfying specific criteria
remove_if (function template)