C++ Library - <deque>

Introduction

Deque is acronym for Double Ended Queue. It is a sequence container that can change it's size runtime. Container is an object that holds data of same type. Sequence containers store elements strictly in linear sequence.

Elements of deque can be scattered in different chunks of memory. Container stores necessary information to allow direct access to any element in constant time. Unlike vectors, deque are not guaranteed to store all it's element at contiguous memory locations. Hence it does not allow direct access to data by offsetting pointers. But it enables direct access to any element using subscript operator [ ].

Deque can shrink or expand as needed from both ends at run time. The storage requirement is fulfilled automatically by internal allocator. Deque provides similar functionality as vectors, but provides efficient way to insert and delete data from any end.

Zero sized deques are also valid. In that case deque.begin() and deque.end() points to same location. But behavior of calling front() or back() is undefined.

Definition

Below is definition of std::deque from <deque> header file

template < class T, class Alloc = allocator<T> > class deque;

Parameters

T − Type of the element contained.

T may be substituted by any other data type including user-defined type.
Alloc − Type of allocator object.

By default, the allocator class template is used, which defines the simplest memory allocation model and is value-independent.

Member types

Following member types can be used as parameters or return type by member functions.

Sr.No.	Member types	Definition
1	value_type	T (First parameter of the template)
2	allocator_type	Alloc (Second parameter of the template)
3	reference	value_type&
4	const_reference	const value_type&
5	pointer	value_type*
6	const_pointer	const value_type*
7	iterator	a random access iterator to value_type
8	const_iterator	a random access iterator to const value_type
9	reverse_iterator	std::reverse_iterator <iterator>
10	const_reverse_iterator	std::reverse_iterator <const_iterator>
11	size_type	size_t
12	difference_type	ptrdiff_t

Functions from <deque>

Below is list of all methods from <deque> header.

Constructors

Sr.No.	Method & Description
1	deque::deque `default constructor` Constructs an empty deque with zero element.
2	deque::deque `fill constructor` construct a new deque with `n` elements and assign `val` to each element of deque
3	deque::deque `range constructor` Constructs a deque with as many elements as in range of `first` to `last`.
4	deque::deque `copy constructor` Constructs a deque with copy of each elements present in existing container.
5	deque::deque `move constructor` Constructs a deque with the contents of other using move semantics.
6	deque::deque `initializer list constructor` Constructs a deque from initialize list.

Destructor

Sr.No.	Method & Description
1	deque::~deque Destroys deque object by deallocating it's memory.

Member functions

Sr.No.	Method & Description
1	deque::assign `range version` Assign new values to the deque elements by replacing old ones.
2	deque::assign `fill version` Assign new values to the deque elements by replacing old ones.
3	deque::assign `initializer list version` Assign new values to the deque elements by replacing old ones.
4	deque::at Returns reference to the element present at location `n` in the deque.
5	deque::back Returns a reference to the last element of the deque.
6	deque::begin Return a random access iterator pointing to the first element of the deque.
7	deque::cbegin Returns a constant random access iterator which points to the beginning of the deque.
8	deque::cend Returns a constant random access iterator which points to the beginning of the deque.
9	deque::clear Destroys the deque by removing all elements from the deque and sets size of deque to zero.
10	deque::crbegin Returns a constant reverse iterator which points to the reverser beginning of the container.
11	deque::crend Returns a constant reverse iterator which points to the reverse end of the deque.
12	deque::emplace Extends container by inserting new element at `position`.
13	deque::emplace_back Inserts new element at the end of deque.
14	deque::emplace_front Inserts new element at the beginning of deque.
15	deque::empty Tests whether deque is empty or not.
16	deque::end Returns an iterator which points to `past-the-end element` in the deque container.
17	deque::erase `position version` Removes single element from the the deque.
18	deque::erase `range version` Removes single element from the the deque.
19	deque::front Returns a reference to the first element of the deque
20	deque::get_allocator Returns an allocator associated with deque
21	deque::insert `single element version` Extends container by inserting new element at `position.`
22	deque::insert `fill version` Extends container by inserting new element in the container.
23	deque::insert `range version` Extends container by inserting new element in the container.
24	deque::insert `move version` Extends container by inserting new element in the container.
25	deque::insert `initializer list version` Extends container by inserting new element in the container.
26	deque::max_size Returns the maximum number of elements can be held by deque.
27	deque::operator= `copy version` Assign new contents to the deque by replacing old ones and modifies size if necessary.
28	deque::operator= `move version` Assign new contents to the deque by replacing old ones and modifies size if necessary.
29	deque::operator= `initializer list version` Assign new contents to the deque by replacing old ones and modifies size if necessary.
30	deque::operator[] Returns a reference to the element present at location `n`.
31	deque::pop_back Removes last element from deque and reduces size of deque by one.
32	deque::pop_front Removes first element from deque and reduces size of deque by one.
33	deque::push_back Inserts new element at the end of deque and increases size of deque by one.
34	deque::push_back `move version` Inserts new element at the end of deque and increases size of deque by one.
35	deque::push_front Inserts new element at the front of deque and increases size of deque by one.
36	deque::push_front `move version` Inserts new element at the front of deque and increases size of deque by one.
37	deque::rbegin Returns a reverse iterator which points to the last element of the deque.
38	deque::rend Returns a reverse iterator which points to the reverse end of the deque.
39	deque::resize Changes the size of deque.
40	deque::resize `value version` Changes the size of deque.
41	deque::shrink_to_fit Requests the container to reduce it's capacity to fit its size.
42	deque::size Returns the number of elements present in the deque.
43	deque::swap Exchanges the content of deque with contents of another deque `x`.

Non-member overloaded functions

Sr.No.	Method & Description
1	operator== Tests whether two deques are equal or not.
2	operator!= Tests whether two deques are equal or not.
3	operator< Tests whether first deque is less than other or not.
4	operator<= Tests whether first deque is less than or equal to other or not.
5	operator> Tests whether first deque is greater than other or not.
6	operator>= Tests whether first deque is greater than or equal to other or not.
7	swap Exchanges the contents of two deque.