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

 

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)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

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)

Tables

Iterator invalidation

Member function table

Non-member function table

 

std::deque

Member types
Member functions
deque::deque deque::~deque deque::operator= deque::assign deque::assign_range (C++23)   deque::get_allocator Element access deque::at deque::operator[] deque::front deque::back Iterators deque::begindeque::cbegin (C++11) deque::enddeque::cend (C++11) deque::rbegindeque::crbegin (C++11) deque::renddeque::crend (C++11)	Capacity deque::empty deque::size deque::max_size deque::shrink_to_fit (DR*) Modifiers deque::clear deque::insert deque::insert_range (C++23) deque::emplace deque::erase deque::push_front deque::emplace_front (C++11) deque::prepend_range (C++23) deque::pop_front deque::push_back deque::emplace_back (C++11) deque::append_range (C++23) deque::pop_back deque::resize deque::swap
Non-member functions
operator==operator<=> (C++20) swap(std::deque) erase(std::deque)erase_if(std::deque) (C++20)(C++20)	operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides(C++17)

 

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

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.

If T is not DefaultInsertable into std::deque<T>, the behavior is undefined.

4) Constructs a deque with count copies of elements with value value.

If T is not CopyInsertable into std::deque<T>, the behavior is undefined.

(since C++11)

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

If InputIt does not satisfy the requirements of LegacyInputIterator, overload (4) is called instead with arguments static_cast<size_type>(first), last and alloc.	(until C++11)
This overload participates in overload resolution only if InputIt satisfies the requirements of LegacyInputIterator. If T is not EmplaceConstructible into std::deque<T> from *first, the behavior is undefined.	(since C++11)

6) Constructs a deque with the contents of the range rg. Each iterator in the rg is dereferenced exactly once.

If T is not EmplaceConstructible into std::deque<T> from *ranges::begin(rg), the behavior is undefined.

7-10) Constructs a deque with the contents of other.

7) The copy constructor.

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

(since C++11)

8) The move constructor. 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.

If T is not CopyInsertable into std::deque<T>, the behavior is undefined.

(since C++11)

10) Same as the move constructor, except that alloc is used as the allocator.

If T is not MoveInsertable into std::deque<T>, the behavior is undefined.

11) Equivalent to deque(il.begin(), il.end(), alloc).

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 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

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().

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.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)

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', ' ', '\0'}; 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}

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 InputIt is 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

See also

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