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

 

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)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

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)

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

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

std::swap

Helper classes

std::uses_allocator (C++11)

Deduction guides(C++17)

 

queue() : queue(Container()) {}	(1)	(since C++11)
	(2)
explicit queue( const Container& cont = Container() );			(until C++11)
explicit queue( const Container& cont );			(since C++11)
explicit queue( Container&& cont );		(3)	(since C++11)
queue( const queue& other );		(4)
queue( queue&& other );		(5)	(since C++11)
template< class InputIt > queue( InputIt first, InputIt last );		(6)	(since C++23)
template< class Alloc > explicit queue( const Alloc& alloc );		(7)	(since C++11)
template< class Alloc > queue( const Container& cont, const Alloc& alloc );		(8)	(since C++11)
template< class Alloc > queue( Container&& cont, const Alloc& alloc );		(9)	(since C++11)
template< class Alloc > queue( const queue& other, const Alloc& alloc );		(10)	(since C++11)
template< class Alloc > queue( queue&& other, const Alloc& alloc );		(11)	(since C++11)
template< class InputIt, class Alloc > queue( InputIt first, InputIt last, const Alloc& alloc );		(12)	(since C++23)
template< container-compatible-range<T> R> queue( std::from_range_t, R&& rg );		(13)	(since C++23)
template< container-compatible-range<T> R, class Alloc > queue( std::from_range_t, R&& rg, const Alloc& alloc );		(14)	(since C++23)

Constructs new underlying container of the container adaptor from a variety of data sources.

1) Default constructor. Value-initializes the container.

2) Copy-constructs the underlying container c with the contents of cont. This is also the default constructor. (until C++11)

3) Move-constructs the underlying container c with std::move(cont).

4) Copy constructor. The adaptor is copy-constructed with the contents of other.c. (implicitly declared)

5) Move constructor. The adaptor is constructed with std::move(other.c). (implicitly declared)

6) Constructs the underlying container c with the contents of the range [first, last). This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator.

7-12) These constructors participate in overload resolution only if std::uses_allocator<Container, Alloc>::value is true, that is, if the underlying container is an allocator-aware container (true for all standard library containers that can be used with queue).

7) Constructs the underlying container using alloc as allocator, as if by c(alloc).

8) Constructs the underlying container with the contents of cont and using alloc as allocator, as if by c(cont, alloc).

9) Constructs the underlying container with the contents of cont using move semantics while utilizing alloc as allocator, as if by c(std::move(cont), alloc).

10) Constructs the adaptor with the contents of other.c and using alloc as allocator, as if by c(other.c, alloc).

11) Constructs the adaptor with the contents of other using move semantics while utilizing alloc as allocator, as if by c(std::move(other.c), alloc).

12) Constructs the underlying container with the contents of the range [first, last) using alloc as allocator, as if by c(first, last, alloc). This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator.

13) Constructs the underlying container with ranges::to<Container>(std::forward<R>(rg)).

14) Constructs the underlying container with ranges::to<Container>(std::forward<R>(rg), alloc).

Parameters

alloc	-	allocator to use for all memory allocations of the underlying container
other	-	another container adaptor to be used as source to initialize the underlying container
cont	-	container to be used as source to initialize the underlying container
first, last	-	range of elements [first, last) to initialize with
rg	-	a container compatible range, that is, an input_range whose elements are convertible to T
Type requirements
- Alloc must meet the requirements of Allocator.
- Container must meet the requirements of Container. The constructors taking an allocator parameter participate in overload resolution only if Container meets the requirements of AllocatorAwareContainer.
- InputIt must meet the requirements of LegacyInputIterator.

Complexity

Same as the corresponding operation on the wrapped container.

Notes

Feature-test macro	Value	Std	Comment
__cpp_lib_adaptor_iterator_pair_constructor	202106L	(C++23)	Iterator pair constructors for std::queue and std::stack; overloads (6) and (12)
__cpp_lib_containers_ranges	202202L	(C++23)	Ranges-aware construction and insertion; overloads (13) and (14)

Example

Run this code

#include <cassert>
#include <deque>
#include <iostream>
#include <memory>
#include <ranges>
#include <queue>
 
int main()
{
    std::queue<int> c1;
    c1.push(5);
    assert(c1.size() == 1);
 
    std::queue<int> c2(c1);
    assert(c2.size() == 1);
 
    std::deque<int> deq {3, 1, 4, 1, 5};
    std::queue<int> c3(deq); // overload (2)
    assert(c3.size() == 5);
 
#   ifdef __cpp_lib_adaptor_iterator_pair_constructor
    const auto il = {2, 7, 1, 8, 2};
    std::queue<int> c4{ il.begin(), il.end() }; // C++23, (6)
    assert(c4.size() == 5);
#   endif
 
#   if __cpp_lib_containers_ranges >= 202202L
    // C++23, overload (13)
    auto c5 = std::queue(std::from_range_t, std::ranges::iota(0, 42));
    assert(c5.size() == 42);
 
    // the same effect with pipe syntax, internally uses overload (13)
    auto c6 = std::ranges::iota(0, 42) | std::ranges::to<std::queue>();
    assert(c6.size() == 42);
 
    std::allocator<int> alloc;
 
    // C++23, overload (14)
    auto c7 = std::queue(std::from_range_t, std::ranges::iota(0, 42), alloc);
    assert(c7.size() == 42);
 
    // the same effect with pipe syntax, internally uses overload (14)
    auto c8 = std::ranges::iota(0, 42) | std::ranges::to<std::queue>(alloc);
    assert(c8.size() == 42);
#   endif
}

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
P0935R0	C++11	default constructor was explicit	made implicit

See also

operator=

assigns values to the container adaptor (public member function)