std::multiset::erase(3)

🦋 std::multiset::erase(3) — C++ Standard Libary

okay bestie, welcome to the std::multiset::erase(3) page from the C++ Standard Libary manual. This is the multiset erase glow-up where you yeet elements out, and yes there are multiple overloads because C++ loves a little drama 💅✨

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✨ NAME ✨

std::multiset::erase — std::multiset::erase (literally the same name twice, iconic 💖)

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🌸 Synopsis 🌸

iterator erase( iterator pos );                          (until C++23)
iterator erase( iterator pos )
    requires(!std::same_as<iterator, const_iterator>);   (since C++23)
iterator erase( const_iterator pos );                    (2) (since C++11)
iterator erase( iterator first, iterator last );         (1) (until C++11)
iterator erase( const_iterator first, const_iterator last ); (3) (since C++11)
size_type erase( const Key& key );                       (4)
template< class K >
size_type erase( K&& x );                                (5) (since C++23)

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💖 Description 💖

Removes specified elements from the container. The order of the remaining equivalent elements is preserved. no cap 🫶

• 1,2) Removes the element at pos.
• Only one overload is provided if iterator and const_iterator are the same type. (since C++11)
• 3) Removes the elements in the range [first, last), which must be a valid range in *this.
• 4) Removes all elements with the key equivalent to key.
• 5) Removes all elements with key that compares equivalent to the value x. This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type, and neither iterator nor const_iterator is implicitly convertible from K. It allows calling this function without constructing an instance of Key.

References and iterators to the erased elements are invalidated. Other references and iterators are not affected. 🚨

The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos. bestie that is not a suggestion, that is the rule 💀

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🎀 Parameters 🎀

• pos — iterator to the element to remove
• first, last — range of elements to remove
• key — key value of the elements to remove
• x — a value of any type that can be transparently compared with a key denoting the elements to remove

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🌈 Return value 🌈

• 1-3) Iterator following the last removed element.
• 4) Number of elements removed.
• 5) Number of elements removed.

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🦋 Exceptions 🦋

• 1-3) Throws nothing.
• 4,5) Any exceptions thrown by the Compare object.

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⭐ Complexity ⭐

Given an instance c of multiset:

• 1,2) Amortized constant
• 3) log(c.size()) + std::distance(first, last)
• 4) log(c.size()) + c.count(key)
• 5) log(c.size()) + c.count(x)

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🧚 Notes 🧚

Feature-test macro vibes, iykyk:

• Feature-test macro: __cpp_lib_associative_heterogeneous_erasure
• Value: 202110L
• Std: (C++23)
• Feature: Heterogeneous erasure in associative containers and unordered associative containers; overload (5)

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🍓 Example 🍓

// Run this code

#include <set>
#include <iostream>

int main()
{
    std::multiset<int> c = {1, 2, 3, 4, 1, 2, 3, 4};

    auto print = [&c]
    {
        std::cout << "c = { ";
        for (int n : c)
            std::cout << n << ' ';
        std::cout << "}\n";
    };
    print();

    std::cout << "Erase all odd numbers:\n";
    for (auto it = c.begin(); it != c.end();)
    {
        if (*it % 2 != 0)
            it = c.erase(it);
        else
            ++it;
    }
    print();

    std::cout << "Erase 1, erased count: " << c.erase(1) << '\n';
    std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
    std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
    print();
}

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🧚 Defect reports 🧚

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• LWG 130, applied to C++98 — behavior as published: the return type of overloads (1) and (3) was void (it is not consistent with the erase() requirement on sequence containers); correct behavior: corrected to iterator.
• LWG 371, applied to C++98 — behavior as published: the order of equivalent elements that are not erased was not guaranteed to be preserved; correct behavior: required to be preserved.
• LWG 2059, applied to C++11 — behavior as published: replacing overload (1) with overload (2) introduced new ambiguity; correct behavior: added overload (1) back.

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👑 See also 👑

• clear — clears the contents (public member function)

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This page’s footer vibes: source http://cppreference.com, version/date 2024.06.10, page std::multiset::erase(3). bye bestie, go erase something iconic 🫶💅✨