std::swap(std::queue)(3)

💖 NAME 💖

std::swap(std::queue) — bestie, it’s literally std::swap(std::queue). We’re in the C++ Standard Libary manual (3), and this page is all about swapping two std::queue containers with main character energy 💅✨

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🦋 Synopsis 🦋

Defined in header <queue> — noted, bestie 🫶

template< class T, class Container >
                                                       (since C++11)
void swap( std::queue<T, Container>& lhs,    (until C++17)

           std::queue<T, Container>& rhs );
template< class T, class Container >

void swap( std::queue<T, Container>& lhs,    (since C++17)
           std::queue<T, Container>& rhs )

                     noexcept(/* see below */);

okay so this thing specializes the std::swap algorithm for std::queue 🔥 It swaps the contents of lhs and rhs, and it calls lhs.swap(rhs). no cap.

Also heads up: (since C++17), this overload only participates in overload resolution if std::is_swappable_v<Container> is true 👑

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🌸 Parameters 🌸

• lhs, rhs — containers whose contents to swap. that’s the whole assignment, bestie 💖

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🎀 Return value 🎀

(none) — literally no return value, periodt 💅

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🦋 Complexity 🦋

Same as swapping the underlying container. lowkey straightforward, highkey iconic ✨

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🔥 Exceptions 🔥

noexcept specification: (since C++17)

noexcept(noexcept(lhs.swap(rhs)))

that’s the vibe check for exceptions, and it passed 🫶

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💜 Notes 💜

Although the overloads of std::swap for container adaptors are introduced in C++11, container adaptors can already be swapped by std::swap in C++98 😭 Such calls to std::swap usually have linear time complexity, but better complexity may be provided. so yeah, it’s giving “works before it was officially cool” 💀✨

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🌈 Example 🌈

// Run this code

#include <algorithm>
#include <iostream>
#include <queue>

int main()
{
    std::queue<int> alice;
    std::queue<int> bob;

    auto print = [](const auto& title, const auto& cont)
    {
        std::cout << title << " size=" << cont.size();
        std::cout << " front=" << cont.front();
        std::cout << " back=" << cont.back() << '\n';
    };

    for (int i = 1; i < 4; ++i)
        alice.push(i);
    for (int i = 7; i < 11; ++i)
        bob.push(i);

    // Print state before swap
    print("Alice:", alice);
    print("Bob  :", bob);

    std::cout << "-- SWAP\n";
    std::swap(alice, bob);

    // Print state after swap
    print("Alice:", alice);
    print("Bob  :", bob);
}

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⭐ Output ⭐

Alice: size=3 front=1 back=3
Bob  : size=4 front=7 back=10
-- SWAP
Alice: size=4 front=7 back=10
Bob  : size=3 front=1 back=3

slay, Alice and Bob really traded places and ate 💅🔥

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👑 See also 👑

• swap — swaps the contents; (C++11) (public member function) 🫶

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💀 Category 💀

• * conditionally noexcept

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okay bye bestie 💜 this page is from http://cppreference.com, dated 2024.06.10, and the page id is std::swap(std::queue)(3) 🎀✨🦋