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std::deque<T,Allocator>::deque

deque();	(1)
explicit deque( const Allocator& alloc );	(2)
	(3)
explicit deque( size_type count, const T& value = T(), const Allocator& alloc = Allocator());		(until C++11)
deque( size_type count, const T& value, const Allocator& alloc = Allocator());		(since C++11)
	(4)
explicit deque( size_type count );		(since C++11) (until C++14)
explicit deque( size_type count, const Allocator& alloc = Allocator() );		(since C++14)
template< class InputIt > deque( InputIt first, InputIt last, const Allocator& alloc = Allocator() );	(5)
deque( const deque& other );	(6)
deque( const deque& other, const Allocator& alloc );	(7)	(since C++11)
deque( deque&& other );	(8)	(since C++11)
deque( deque&& other, const Allocator& alloc );	(9)	(since C++11)
deque( std::initializer_list<T> init, const Allocator& alloc = Allocator() );	(10)	(since C++11)
template< container-compatible-range<T> R > deque( std::from_range_t, R&& rg, const Allocator& alloc = Allocator() );	(11)	(since C++23)

Constructs a new container from a variety of data sources, optionally using a user supplied allocator alloc.

1) Default constructor. Constructs an empty container with a default-constructed allocator.

2) Constructs an empty container with the given allocator alloc.

3) Constructs the container with count copies of elements with value value.

4) Constructs the container with count default-inserted instances of T. No copies are made.

5) Constructs the container with the contents of the range [first, last).

This constructor has the same effect as `deque(static_cast<size_type>(first), static_cast<value_type>(last), a)` if `InputIt` is an integral type.	(until C++11)
This overload participates in overload resolution only if `InputIt` satisfies LegacyInputIterator, to avoid ambiguity with the overload (3).	(since C++11)

6) Copy constructor. Constructs the container with the copy of the contents of other.

The allocator is obtained as if by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction( other.get_allocator()).

(since C++11)

7) Constructs the container with the copy of the contents of other, using alloc as the allocator.

During class template argument deduction, only the first argument contributes to the deduction of the container's Allocator template parameter.

(since C++23)

8) Move constructor. Constructs the container with the contents of other using move semantics. Allocator is obtained by move-construction from the allocator belonging to other.

9) Allocator-extended move constructor. Using alloc as the allocator for the new container, moving the contents from other; if alloc != other.get_allocator(), this results in an element-wise move.

During class template argument deduction, only the first argument contributes to the deduction of the container's Allocator template parameter.

(since C++23)

10) Constructs the container with the contents of the initializer list init.

11) Constructs the container with the contents of the range rg.

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 range `[first,` `last)` to copy the elements from
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, that is, an `input_range` whose elements are convertible to `T`

Complexity

1-2) Constant.

3-4) Linear in count.

5) Linear in distance between first and last.

6-7) Linear in size of other.

8) Constant.

9) Linear if alloc != other.get_allocator(), otherwise constant.

10) Linear in size of init.

11) Linear in ranges::distance(rg).

Exceptions

Calls to Allocator::allocate may throw.

Notes

After container move construction (overload (8)), 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.rev.reqmts]/17, and a more direct guarantee is under consideration via LWG 2321.

Feature-test macro	Value	Std	Comment
`__cpp_lib_containers_ranges`	202202L	(C++23)	Ranges-aware construction and insertion; overload (11)

Example

#include <deque>
#include <iostream>
#include <string>
 
template<typename T>
std::ostream& operator<<(std::ostream& s, const std::deque<T>& v)
{
    s.put('{');
    char comma[3]{'\0', ' ', '\0'};
    for (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;
}

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}

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 2193	C++11	the default constructor is explicit	made non-explicit

assign	assigns values to the container (public member function)
operator=	assigns values to the container (public member function)