Showing content from https://cplusplus.com/deque below:
class template
<deque>
std::deque
template < class T, class Alloc = allocator<T> > class deque;
Double ended queue
deque (usually pronounced like "deck") is an irregular acronym of double-ended queue. Double-ended queues are sequence containers with dynamic sizes that can be expanded or contracted on both ends (either its front or its back).
Specific libraries may implement deques in different ways, generally as some form of dynamic array. But in any case, they allow for the individual elements to be accessed directly through random access iterators, with storage handled automatically by expanding and contracting the container as needed.
Therefore, they provide a functionality similar to vectors, but with efficient insertion and deletion of elements also at the beginning of the sequence, and not only at its end. But, unlike vectors, deques are not guaranteed to store all its elements in contiguous storage locations: accessing elements in a deque by offsetting a pointer to another element causes undefined behavior.
Both vectors and deques provide a very similar interface and can be used for similar purposes, but internally both work in quite different ways: While vectors use a single array that needs to be occasionally reallocated for growth, the elements of a deque can be scattered in different chunks of storage, with the container keeping the necessary information internally to provide direct access to any of its elements in constant time and with a uniform sequential interface (through iterators). Therefore, deques are a little more complex internally than vectors, but this allows them to grow more efficiently under certain circumstances, especially with very long sequences, where reallocations become more expensive.
For operations that involve frequent insertion or removals of elements at positions other than the beginning or the end, deques perform worse and have less consistent iterators and references than lists and forward lists.
Container properties
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Sequence
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Elements in sequence containers are ordered in a strict linear sequence. Individual elements are accessed by their position in this sequence.
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Dynamic array
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Generally implemented as a dynamic array, it allows direct access to any element in the sequence and provides relatively fast addition/removal of elements at the beginning or the end of the sequence.
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Allocator-aware
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The container uses an allocator object to dynamically handle its storage needs.
Template parameters
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T
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Type of the elements.
Aliased as member type deque::value_type.
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Alloc
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Type of the allocator object used to define the storage allocation model. By default, the allocator class template is used, which defines the simplest memory allocation model and is value-independent.
Aliased as member type deque::allocator_type.
Member types member type definition notes value_type The first template parameter (T) allocator_type The second template parameter (Alloc) defaults to: allocator<value_type> reference allocator_type::reference for the default allocator: value_type& const_reference allocator_type::const_reference for the default allocator: const value_type& pointer allocator_type::pointer for the default allocator: value_type* const_pointer allocator_type::const_pointer for the default allocator: const value_type* iterator a random access iterator to value_type convertible to const_iterator const_iterator a random access iterator to const value_type reverse_iterator reverse_iterator<iterator> const_reverse_iterator reverse_iterator<const_iterator> difference_type a signed integral type, identical to: iterator_traits<iterator>::difference_type usually the same as ptrdiff_t size_type an unsigned integral type that can represent any non-negative value of difference_type usually the same as size_t member type definition notes value_type The first template parameter (T) allocator_type The second template parameter (Alloc) defaults to: allocator<value_type> reference value_type& const_reference const value_type& pointer allocator_traits<allocator_type>::pointer for the default allocator: value_type* const_pointer allocator_traits<allocator_type>::const_pointer for the default allocator: const value_type* iterator a random access iterator to value_type convertible to const_iterator const_iterator a random access iterator to const value_type reverse_iterator reverse_iterator<iterator> const_reverse_iterator reverse_iterator<const_iterator> difference_type a signed integral type, identical to:
iterator_traits<iterator>::difference_type usually the same as ptrdiff_t size_type an unsigned integral type that can represent any non-negative value of difference_type usually the same as size_t
Member functions
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(constructor)
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Construct deque container (public member function)
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(destructor)
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Deque destructor (public member function)
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operator=
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Assign content (public member function)
Iterators:
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begin
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Return iterator to beginning (public member function)
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end
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Return iterator to end (public member function)
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rbegin
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Return reverse iterator to reverse beginning (public member function)
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rend
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Return reverse iterator to reverse end (public member function)
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cbegin
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Return const_iterator to beginning (public member function)
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cend
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Return const_iterator to end (public member function)
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crbegin
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Return const_reverse_iterator to reverse beginning (public member function)
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crend
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Return const_reverse_iterator to reverse end (public member function)
Capacity:
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size
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Return size (public member function)
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max_size
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Return maximum size (public member function)
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resize
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Change size (public member function)
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empty
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Test whether container is empty (public member function)
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shrink_to_fit
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Shrink to fit (public member function)
Element access:
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operator[]
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Access element (public member function)
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at
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Access element (public member function)
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front
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Access first element (public member function)
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back
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Access last element (public member function)
Modifiers:
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assign
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Assign container content (public member function)
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push_back
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Add element at the end (public member function)
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push_front
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Insert element at beginning (public member function)
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pop_back
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Delete last element (public member function)
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pop_front
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Delete first element (public member function)
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insert
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Insert elements (public member function)
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erase
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Erase elements (public member function)
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swap
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Swap content (public member function)
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clear
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Clear content (public member function)
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emplace
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Construct and insert element (public member function)
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emplace_front
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Construct and insert element at beginning (public member function)
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emplace_back
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Construct and insert element at the end (public member function)
Allocator:
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get_allocator
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Get allocator (public member function)
Non-member functions overloads
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relational operators
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Relational operators for deque (function)
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swap
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Exchanges the contents of two deque containers (function template)
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