NAME¶

std::erase_if(std::unordered_multimap) - std::erase_if(std::unordered_multimap)

Synopsis¶

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

erase_if( std::unordered_multimap<Key,T,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_map>
#include <iostream>

template<typename Os, typename Container>
inline Os& operator<<(Os& os, Container const& cont)
{
os << "{";
for (const auto& item : cont) {
os << "{" << item.first << ", " << item.second << "}";
}
return os << "}";
}

int main()
{
std::unordered_multimap<int, char> data {{1, 'a'},{2, 'b'},{3, 'c'},{4, 'd'},
{5, 'e'},{4, 'f'},{5, 'g'},{5, 'g'}};
std::cout << "Original:\n" << data << '\n';

const auto count = std::erase_if(data, [](const auto& item) {
auto const& [key, value] = item;
return (key & 1) == 1;
});

std::cout << "Erase items with odd keys:\n" << data << '\n'
<< count << " items removed.\n";
}

Possible output:¶

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

See also¶

remove removes elements satisfying specific criteria
remove_if (function template)