NAME¶

std::erase_if(std::unordered_set) - std::erase_if(std::unordered_set)

Synopsis¶

Defined in header <unordered_set>
template< class Key, class Hash, class KeyEqual, class Alloc,

class Pred >
std::unordered_set<Key, Hash, KeyEqual, Alloc>::size_type (since C++20)
erase_if( std::unordered_set<Key, Hash, KeyEqual, Alloc>& c,

Pred pred );

Erases all elements that satisfy the predicate pred from c.

Equivalent to

auto old_size = c.size();
for (auto first = c.begin(), last = c.end(); first != last;)
{
if (pred(*first))
first = c.erase(first);
else
++first;
}
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 <iostream>
#include <unordered_set>

void println(auto rem, auto const& container)
{
std::cout << rem << '{';
for (char sep[]{0, ' ', 0}; const auto& item : container)
std::cout << sep << item, *sep = ',';
std::cout << "}\n";
}

int main()
{
std::unordered_set data{3, 3, 4, 5, 5, 6, 6, 7, 2, 1, 0};
println("Original:\n", data);

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

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

println("Erase all items divisible by 3:\n", data);
std::cout << count << " items erased.\n";
}

Possible output:¶

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

See also¶

remove removes elements satisfying specific criteria
remove_if (function template)