NAME¶

std::erase_if(std::multimap) - std::erase_if(std::multimap)

Synopsis¶

Defined in header <map>
template< class Key, class T, class Compare, class Alloc, class Pred
>
(since C++20)
typename std::multimap<Key,T,Compare,Alloc>::size_type

erase_if( std::multimap<Key,T,Compare,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 <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::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";
}

Output:¶

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

See also¶

remove removes elements satisfying specific criteria
remove_if (function template)