std::queue::queue - cppreference.com (2024)

[edit template]

C++

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[edit]

Containers library

See Also

Queue Data Structure - GeeksforGeeks

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)	(implicitly declared)
queue( queue&& other );		(5)	(since C++11) (implicitly declared)
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.

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

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).

1 Parameters
2 Complexity
3 Notes
4 Example
5 Defect reports
6 See also

[edit] 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.

[edit] Complexity

Same as the corresponding operation on the wrapped container.

[edit] Notes

Feature-test macro	Value	Std	Feature
__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)

[edit] 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}

[edit] 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

[edit] See also

operator=

assigns values to the container adaptor
(public member function) [edit]

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

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)

std::queue<T,Container>::queue - cppreference.com (2024)

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