Defined in header <map> | ||
|---|---|---|
template< class Key, class T, class Compare, class Alloc, class Pred >
typename std::map<Key, T, Compare, Alloc>::size_type
erase_if( std::map<Key, T, Compare, Alloc>& c, Pred pred );
| (since C++20) |
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();| c | - | container from which to erase |
| pred | - | predicate that returns true if the element should be erased |
The number of erased elements.
Linear.
#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::map<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}{5, e}}
Erase items with odd keys:
{{2, b}{4, d}}
3 items removed.| removes elements satisfying specific criteria (function template) |
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