std::erase_...d_multiset)(3)

✨ std::erase_if(std::unordered_multiset) ✨

okay so welcome to the std::erase_...d_multiset)(3) page from the C++ Standard Libary manual — yes bestie, that manual name is spelled exactly like that, we’re not fixing it, we’re honoring it 💅. this is giving C++20 container-cleanup main character energy and I’m obsessed.

🌸 NAME 🌸

std::erase_if(std::unordered_multiset) — and the description is literally the same thing again: std::erase_if(std::unordered_multiset). no cap, that’s the name and the one-liner, periodt 🫶.

🌈 Synopsis 🌈

Defined in header <unordered_set>:

template< class Key, class Hash, class KeyEqual, class Alloc,

          class Pred >
std::unordered_multiset<Key, Hash, KeyEqual, Alloc>::size_type
(since C++20)
    erase_if( std::unordered_multiset<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. it’s the unordered multiset getting the glow-up ✨
• pred — predicate that returns true if the element should be erased. if it says true, that element is outta here 💅

🎁 Return value 🎁

The number of erased elements. that’s the count, bestie — the size_type situation fr fr 💖

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

👀 See also 👀

• remove — removes elements satisfying specific criteria
• remove_if — (function template)

that’s the whole page, bestie 🫶 source/version: http://cppreference.com, 2024.06.10, page std::erase_...d_multiset)(3). mwah 💋✨