NAME¶

std::deque::deque - std::deque::deque

Synopsis¶

deque(); (1)
explicit deque( const Allocator& alloc ); (2)
explicit deque( size_type count,

const T& value = T(), (until C++11)

const Allocator& alloc =
Allocator() );
deque( size_type count,

const T& value, (since C++11)

const Allocator& alloc = Allocator() );
explicit deque( size_type count ); (since C++11)
(until C++14)
explicit deque( size_type count,
const Allocator& alloc = (since C++14)
Allocator() );
template< class InputIt > (3)

deque( InputIt first, InputIt last, (5)

const Allocator& alloc = Allocator() );
deque( const deque& other ); (4) (6)
deque( const deque& other, const Allocator& (7) (since C++11)
alloc );
deque( deque&& other ); (8) (since C++11)
deque( deque&& other, const Allocator& alloc ); (9) (since C++11)
deque( std::initializer_list<T> init, (10) (since C++11)
const Allocator& alloc = Allocator() );
template< container-compatible-range<T> R >

deque( std::from_range_t, R&& rg, (11) (since C++23)

const Allocator& alloc = Allocator() );

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) (until C++11)
if InputIt is an integral type.
This overload participates in overload resolution only if InputIt
satisfies LegacyInputIterator, to avoid ambiguity with the overload (since C++11)
(3).

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

The allocator is obtained as if by calling (since
std::allocator_traits<allocator_type>::select_on_container_copy_construction( C++11)
other.get_allocator()).

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 (since C++23)
parameter.

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 (since C++23)
parameter.

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.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 (11)

Example¶

// Run this code

#include <iostream>
#include <string>
#include <deque>

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;

auto const rg = {"cat", "cow", "crow"};
#ifdef __cpp_lib_containers_ranges
std::deque<std::string> words5(std::from_range, rg); // overload (11)
#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
the complexity requirement of
LWG 144 C++98 overload (5) was the same changed to linear complexity
as that of the corresponding
overload of std::vector
the complexity requirement of changed to linear in
LWG 237 C++98 overload std::distance(first, last)
(5) was linear in first - last
for overload (4), the elements in
LWG 868 C++98 the container were default they are value-initialized
constructed
LWG 2193 C++11 the default constructor is explicit made non-explicit

See also¶

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