NAME¶

std::queue::queue - std::queue::queue

Synopsis¶

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

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).

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 Feature
Iterator pair
constructors for
__cpp_lib_adaptor_iterator_pair_constructor 202106L (C++23) std::queue and
std::stack; overloads
(6) and (12)
Ranges-aware
__cpp_lib_containers_ranges 202202L (C++23) 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)