std::erase_...ordered_set)(3)

💖 NAME 💖

std::erase_if(std::unordered_set) — std::erase_if(std::unordered_set).

Okay bestie, this is the std::erase_...ordered_set)(3) page from the C++ Standard Libary manual (and yes, “Libary” is literally how it’s spelled in the header 😭). The main character here is std::erase_if(std::unordered_set), and it’s here to erase elements from an unordered_set when your predicate says so. Slay.

✨ Synopsis ✨

Defined in header <unordered_set>. No cap.

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 );

It erases all elements that satisfy the predicate pred from c. It’s giving selective-cleanup energy, honestly. 💅

Equivalent to this loop:

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_set you’re cleaning out, bestie.
• pred — predicate that returns true if the element should be erased. true means bye-bye 👋.

🎀 Return value 🎀

The number of erased elements. That’s the return value, periodt. 💖

🦋 Complexity 🦋

Linear. That’s the whole complexity note, bestie.

🔥 Example 🔥

Run this code (the comment in the code literally says so):

// 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).

Okay that’s the page 💅 source: http://cppreference.com; version/date: 2024.06.10; and it’s the std::erase_...ordered_set)(3) page from the C++ Standard Libary manual. Bye bestie, go erase with main character energy 🫶