std::erase_...at_multiset)(3)

💅 NAME

Okay bestie, this page is for std::erase_if(std::flat_multiset) — literally std::erase_if(std::flat_multiset). It’s a C++ Standard Library manual page, and the page title is std::erase_...at_multiset)(3).

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✨ Synopsis ✨

Defined in header <flat_set>:

template< class Key, class Compare, class KeyContainer,
          class Pred >
std::flat_multiset<Key, Compare, KeyContainer>::size_type
(since C++23)
    erase_if( std::flat_multiset<Key, Compare, KeyContainer>& c,
              Pred pred );

So what does it do? It erases all elements that satisfy the predicate pred from c. The predicate pred is satisfied if the expression bool(pred(std::as_const(e))) is true, where e is some element in c. 🫶

Vibe check: Key must be MoveAssignable. Otherwise, the behavior is undefined. Not me risking UB, bestie 😭

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🎀 Parameters 🎀

• c — the container adaptor from which to erase, aka the one getting a little cleanup.
• pred — the predicate that returns true if the element should be erased</c>. It’s giving “you gotta go” energy.

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🌸 Return value 🌸

It returns the number of erased elements. Simple. Iconic. Periodt.

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🦋 Complexity 🦋

Exactly c.size() applications of the predicate pred. No extra chaos, just that many calls.

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💜 Exceptions 💜

If erase_if throws, c remains in a valid but unspecified (maybe empty) state. So yes, valid-ish, but don’t assume it still looks the same, bestie.

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👑 Notes 👑

The algorithm is stable, that is, the order of elements that are not deleted remains unchanged. We love a stable queen 🌈

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🍓 Example 🍓

Run this code, bestie:

#include <iostream>
#include <flat_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::flat_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";
}

Output

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

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👀 See also 👀

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

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That’s the whole page, bestie 🫶 — source is http://cppreference.com, dated 2024.06.10, page std::erase_...at_multiset)(3). Mwah 💋✨