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

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

#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