std::deque<T,Allocator>::deque
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std::deque
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deque::deque
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(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
deque() : deque(Allocator()) {}
(1)
(since C++11) (constexpr since C++26)
(2)
explicit deque( const Allocator& alloc = Allocator() );
(until C++11)
explicit deque( const Allocator& alloc );
(since C++11) (constexpr since C++26)
explicit deque( size_type count,
const Allocator& alloc = Allocator() );
(3)
(since C++11) const Allocator& alloc = Allocator() );
(constexpr since C++26)
(4)
explicit deque( size_type count, const T& value = T(),
const Allocator& alloc = Allocator() );
(until C++11)
const Allocator& alloc = Allocator() );
deque( size_type count, const T& value,
const Allocator& alloc = Allocator() );
(since C++11) const Allocator& alloc = Allocator() );
(constexpr since C++26)
template< class InputIt >
(5)
(constexpr since C++26)
deque( InputIt first, InputIt last,
template< container-compatible-range <T> R >
(6)
(since C++23) deque( std::from_range_t, R&& rg,
(constexpr since C++26)
deque( const deque& other );
(7)
(constexpr since C++26)
deque( deque&& other );
(8)
(since C++11) (constexpr since C++26)
(9)
deque( const deque& other, const Allocator& alloc );
(since C++11) (until C++23)
deque( const deque& other,
const std::type_identity_t <Allocator>& alloc );
(since C++23) const std::type_identity_t <Allocator>& alloc );
(constexpr since C++26)
(10)
deque( deque&& other, const Allocator& alloc );
(since C++11) (until C++23)
deque( deque&& other, const std::type_identity_t <Allocator>& alloc );
(since C++23) (constexpr since C++26)
deque( std::initializer_list <T> init,
const Allocator& alloc = Allocator() );
(11)
(since C++11) const Allocator& alloc = Allocator() );
(constexpr since C++26)
Constructs a new deque from a variety of data sources, optionally using a user supplied allocator alloc.
1) The default constructor since C++11. Constructs an empty
deque with a default-constructed allocator. If
Allocator is not DefaultConstructible, the behavior is undefined.2) The default constructor until C++11. Constructs an empty
deque with the given allocator alloc.3) Constructs a
deque with count default-inserted objects of T. No copies are made.4) Constructs a
deque with count copies of elements with value value.
If T is not CopyInsertable into deque, the behavior is undefined.
5) Constructs a
deque with the contents of the range [first, last). Each iterator in [first, last) is dereferenced exactly once.
If InputIt does not satisfy the requirements of LegacyInputIterator, overload (4) is called instead with arguments static_cast<size_type>(first), last and alloc.
This overload participates in overload resolution only if InputIt satisfies the requirements of LegacyInputIterator.
If T is not EmplaceConstructible into deque from *first, the behavior is undefined.
6) Constructs a
deque with the contents of the range rg. Each iterator in rg is dereferenced exactly once.7) The copy constructor. Constructs a
deque with the contents of other.
The allocator is obtained as if by calling
std::allocator_traits <Allocator>::select_on_container_copy_construction
(other.get_allocator()).
8) The move constructor. Constructs a
deque with the contents of other. The allocator is obtained by move construction from other.get_allocator().9) Same as the copy constructor, except that alloc is used as the allocator.
10) Same as the move constructor, except that alloc is used as the allocator.
11) Equivalent to deque(il.begin(), il.end(), alloc).
[edit] Parameters
alloc
-
allocator to use for all memory allocations of this container
count
-
the size of the container
value
-
the value to initialize elements of the container with
first, last
-
the pair of iterators defining the source range of elements to copy
other
-
another container to be used as source to initialize the elements of the container with
init
-
initializer list to initialize the elements of the container with
rg
-
a container compatible range
[edit] Complexity
1,2) Constant.
3,4) Linear in count.
5) Linear in std::distance (first, last).
6) Linear in ranges::distance (rg).
7) Linear in other.size().
8) Constant.
9) Linear in other.size().
10) Linear in other.size() if alloc != other.get_allocator(), otherwise constant.
11) Linear in init.size().
[edit] Exceptions
Calls to Allocator::allocate may throw.
[edit] Notes
After container move construction (overloads (8) and (10)), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in [container.reqmts]/67, and a more direct guarantee is under consideration via LWG issue 2321.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_containers_ranges |
202202L |
(C++23) | Ranges-aware construction and insertion; overload (6) |
[edit] Example
Run this code
#include <deque> #include <iostream> #include <string> template<typename T> std::ostream & operator<<(std::ostream & s, const std::deque <T>& v) { s.put('{'); for (char comma[]{'0円', ' ', '0円'}; const auto& e : v) s << comma << e, comma[0] = ','; return s << "}\n"; } int main() { // C++11 initializer list syntax: std::deque <std::string > words1{"the", "frogurt", "is", "also", "cursed"}; std::cout << "1: " << words1; // words2 == words1 std::deque <std::string > words2(words1.begin(), words1.end()); std::cout << "2: " << words2; // words3 == words1 std::deque <std::string > words3(words1); std::cout << "3: " << words3; // words4 is {"Mo", "Mo", "Mo", "Mo", "Mo"} std::deque <std::string > words4(5, "Mo"); std::cout << "4: " << words4; const auto rg = {"cat", "cow", "crow"}; #ifdef __cpp_lib_containers_ranges std::deque <std::string > words5(std::from_range, rg); // overload (6) #else std::deque <std::string > words5(rg.begin(), rg.end()); // overload (5) #endif std::cout << "5: " << words5; }
Output:
1: {the, frogurt, is, also, cursed}
2: {the, frogurt, is, also, cursed}
3: {the, frogurt, is, also, cursed}
4: {Mo, Mo, Mo, Mo, Mo}
5: {cat, cow, crow}[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 |
|---|---|---|---|
| LWG 144 | C++98 | the complexity requirement of overload (5) was the same as that of the corresponding overload of std::vector |
changed to linear complexity |
| LWG 237 | C++98 | the complexity requirement of overload (5) was linear in first - last |
changed to linear in std::distance (first, last) |
| LWG 438 | C++98 | overload (5) would only call overload (4) if InputIt is an integral type
|
calls overload (4) if InputItis not an LegacyInputIterator |
| LWG 2193 | C++11 | the default constructor was explicit | made non-explicit |
| LWG 2210 | C++11 | overload (3) did not have an allocator parameter | added the parameter |
| N3346 | C++11 | for overload (3), the elements in the container were value-initialized |
they are default-inserted |