std::queue::swap(3)

✨ NAME ✨

bestie, welcome to std::queue::swap(3) from the C++ Standard Libary ✨ — the manual name is literally std::queue::swap(3), and the NAME line is exactly std::queue::swap - std::queue::swap 💅. It's giving "swap your queue's contents" main character energy, no cap.

---

🦋 Synopsis

void swap( queue& other ) noexcept(/* see below */);  (since C++11)

Exchanges the contents of the container adaptor with those of other. Effectively calls:

using std::swap;
swap(c, other.c);

---

🎀 Parameters

• other — container adaptor to exchange the contents with 💖

---

🌸 Return value

(none) — literally nothing, bestie 🫶

---

🔥 Exceptions

• noexcept specification, (since C++11) and (until C++17):

noexcept(noexcept(swap(c, other.c)))

In the expression above, the identifier swap is looked up in the same manner as the one used by the C++17 std::is_nothrow_swappable trait.

• noexcept specification, (since C++17):

noexcept(std::is_nothrow_swappable_v<Container>)

---

🦋 Complexity

Same as underlying container (typically constant) ✨

---

💜 Notes

Some implementations (e.g. libc++) provide the swap member function as an extension to pre-C++11 modes 👑

---

🎀 Example

okay so // Run this code — here's the whole example, bestie:

#include <iostream>
#include <concepts>
#include <queue>
#include <string>
#include <string_view>
#include <vector>

template<typename Adaptor>
requires (std::ranges::input_range<typename Adaptor::container_type>)
void print(std::string_view name, const Adaptor& adaptor)
{
    struct Printer : Adaptor // to use protected Adaptor::Container c;
    {
        void print(std::string_view name) const
        {
            std::cout << name << " [" << std::size(this->c) << "]: ";
            for (auto const& elem : this->c)
                std::cout << elem << ' ';
            std::cout << '\n';
        }
    };

    static_cast<Printer const&>(adaptor).print(name);
}

int main()
{
    std::vector<std::string> v1{"1","2","3","4"},
                             v2{"Ɐ","B","Ɔ","D","Ǝ"};

    std::queue s1(std::move(v1));
    std::queue s2(std::move(v2));

    print("s1", s1);
    print("s2", s2);

    s1.swap(s2);

    print("s1", s1);
    print("s2", s2);
}

Output:

s1 [4]: 4 3 2 1
s2 [5]: Ǝ D Ɔ B Ɐ
s1 [5]: Ǝ D Ɔ B Ɐ
s2 [4]: 4 3 2 1

---

💀 Defect reports

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

• LWG 2456 — applied to C++11; behavior as published: the noexcept specification is ill-formed; correct behavior: made to work 💀

---

🌈 See also

• std::swap(std::queue) specializes the std::swap algorithm — (C++11) (function template) ⭐

---

👑 Category

• conditionally noexcept

---

okay bestie, that's the whole page 💖 — source/version: http://cppreference.com, dated 2024.06.10 🌸