std::erase_if (std::unordered_multimap)

Since C++20

Header: <unordered_map>

Erases all elements that satisfy the predicate pred from c.

# Declarations

template< class Key, class T, class Hash, class KeyEqual, class Alloc,
class Pred >
std::unordered_multimap<Key, T, Hash, KeyEqual, Alloc>::size_type
erase_if( std::unordered_multimap<Key, T, Hash, KeyEqual, Alloc>& c,
Pred pred );

(since C++20)

# Parameters

# Return value

The number of erased elements.

# Example

#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";
}

# See also