NAME¶

std::erase_if(std::unordered_multiset) - std::erase_if(std::unordered_multiset)

Synopsis¶

Defined in header <unordered_set>
template< class Key, class Hash, class KeyEqual, class Alloc, class Pred >
(since
typename std::unordered_multiset<Key,Hash,KeyEqual,Alloc>::size_type C++20)

erase_if( std::unordered_multiset<Key,Hash,KeyEqual,Alloc>& c, Pred pred );

Erases all elements that satisfy the predicate pred from the container. Equivalent
to

auto old_size = c.size();
for (auto i = c.begin(), last = c.end(); i != last; ) {
if (pred(*i)) {
i = c.erase(i);
} else {
++i;
}
}
return old_size - c.size();

Parameters¶

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

Return value¶

The number of erased elements.

Complexity¶

Linear.

Example¶

// Run this code

#include <unordered_set>
#include <iostream>

template<typename Os, typename Container>
inline Os& operator<<(Os& os, Container const& container)
{
os << "{ ";
for (const auto& item : container) {
os << item << ' ';
}
return os << "}";
}

int main()
{
std::unordered_multiset data { 3, 3, 4, 5, 5, 6, 6, 7, 2, 1, 0 };
std::cout << "Original:\n" << data << '\n';

auto divisible_by_3 = [](auto const& x) { return (x % 3) == 0; };

const auto count = std::erase_if(data, divisible_by_3);

std::cout << "Erase all items divisible by 3:\n" << data << '\n'
<< count << " items erased.\n";
}

Possible output:¶

Original:
{ 0 1 2 7 6 6 5 5 4 3 3 }
Erase all items divisible by 3:
{ 1 2 7 5 5 4 }
5 items erased.

See also¶

remove removes elements satisfying specific criteria
remove_if (function template)