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.
DefinitionBelow 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.
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 constructorConstructs an empty deque with zero element.
2 deque::deque fill constructorconstruct a new deque with n elements and assign val to each element of deque
3 deque::deque range constructorConstructs a deque with as many elements as in range of first to last.
4 deque::deque copy constructorConstructs a deque with copy of each elements present in existing container.
5 deque::deque move constructorConstructs a deque with the contents of other using move semantics.
6 deque::deque initializer list constructorConstructs a deque from initialize list.
Destructor Sr.No. Method & Description 1 deque::~dequeDestroys deque object by deallocating it's memory.
Member functions Sr.No. Method & Description 1 deque::assignAssign new values to the deque elements by replacing old ones.
2 deque::atReturns reference to the element present at location n in the deque.
3 deque::backReturns a reference to the last element of the deque.
4 deque::beginReturn a random access iterator pointing to the first element of the deque.
5 deque::cbeginReturns a constant random access iterator which points to the beginning of the deque.
6 deque::cendReturns a constant random access iterator which points to the beginning of the deque.
7 deque::clearDestroys the deque by removing all elements from the deque and sets size of deque to zero.
8 deque::crbeginReturns a constant reverse iterator which points to the reverser beginning of the container.
9 deque::crendReturns a constant reverse iterator which points to the reverse end of the deque.
10 deque::emplaceExtends container by inserting new element at position.
11 deque::emplace_backInserts new element at the end of deque.
12 deque::emplace_frontInserts new element at the beginning of deque.
13 deque::emptyTests whether deque is empty or not.
14 deque::endReturns an iterator which points to past-the-end element in the deque container.
15 deque::eraseRemoves single element from the the deque.
16 deque::frontReturns a reference to the first element of the deque
17 deque::get_allocatorReturns an allocator associated with deque
18 deque::insertExtends container by inserting new element in the deque.
19 deque::max_sizeReturns the maximum number of elements can be held by deque.
20 deque::operator=Assign new contents to the deque by replacing old ones and modifies size if necessary.
21 deque::operator[]Returns a reference to the element present at location n.
22 deque::pop_backRemoves last element from deque and reduces size of deque by one.
23 deque::pop_frontRemoves first element from deque and reduces size of deque by one.
24 deque::push_backInserts new element at the end of deque and increases size of deque by one.
25 deque::push_frontInserts new element at the front of deque and increases size of deque by one.
26 deque::rbeginReturns a reverse iterator which points to the last element of the deque.
27 deque::rendReturns a reverse iterator which points to the reverse end of the deque.
28 deque::resizeChanges the size of deque.
29 deque::shrink_to_fitRequests the container to reduce it's capacity to fit its size.
30 deque::sizeReturns the number of elements present in the deque.
31 deque::swapExchanges the content of deque with contents of another deque.
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.
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