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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

Tables

Iterator invalidation

Member function table

Non-member function table

 

std::queue

Member functions

queue::queue

queue::~queue

queue::operator=

Element access

queue::front

queue::back

Capacity

queue::empty

queue::size

Modifiers

queue::push

queue::push_range (C++23)

queue::emplace (C++11)

queue::pop

queue::swap (C++11)

Non-member functions

swap(std::queue) (C++11)

operator==operator!=operator<operator>operator<=operator>=operator<=> (C++20)

Helper classes

uses_allocator<std::queue> (C++11)

formatter<std::queue> (C++23)

Deduction guides(C++17)

 

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)