# std::queue<T,Container>::swap

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< cpp‎ | container‎ | queue

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)

### Exceptions

`noexcept` specification: 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. | (since C++11) (until C++17)
`noexcept` specification: noexcept(std::is_nothrow_swappable_v<Container>) | (since C++17)

### 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

Run this code

    #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.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2456 | C++11 | the `noexcept` specification is ill-formed | made to work

### See also

std::swap(std::queue) (C++11) | specializes the std::swap algorithm (function template)

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