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 >
std::unordered_multimap<Key, T, Hash, KeyEqual, Alloc>::size_type (since C++20)
erase_if( std::unordered_multimap<Key, T, 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_map>

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

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

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

println("Erase items with odd keys:\n", data);
std::cout << 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)