class template
<vector>

std::vector

template < class T, class Alloc = allocator<T> > class vector; // generic template
Vector
Vectors are sequence containers representing arrays that can change in size.

Just like arrays, vectors use contiguous storage locations for their elements, which means that their elements can also be accessed using offsets on regular pointers to its elements, and just as efficiently as in arrays. But unlike arrays, their size can change dynamically, with their storage being handled automatically by the container.

Internally, vectors use a dynamically allocated array to store their elements. This array may need to be reallocated in order to grow in size when new elements are inserted, which implies allocating a new array and moving all elements to it. This is a relatively expensive task in terms of processing time, and thus, vectors do not reallocate each time an element is added to the container.

Instead, vector containers may allocate some extra storage to accommodate for possible growth, and thus the container may have an actual capacity greater than the storage strictly needed to contain its elements (i.e., its size). Libraries can implement different strategies for growth to balance between memory usage and reallocations, but in any case, reallocations should only happen at logarithmically growing intervals of size so that the insertion of individual elements at the end of the vector can be provided with amortized constant time complexity (see push_back).

Therefore, compared to arrays, vectors consume more memory in exchange for the ability to manage storage and grow dynamically in an efficient way.

Compared to the other dynamic sequence containers (deques, lists and forward_lists), vectors are very efficient accessing its elements (just like arrays) and relatively efficient adding or removing elements from its end. For operations that involve inserting or removing elements at positions other than the end, they perform worse than the others, and have less consistent iterators and references than lists and forward_lists.

Container properties

Sequence
Elements in sequence containers are ordered in a strict linear sequence. Individual elements are accessed by their position in this sequence.
Dynamic array
Allows direct access to any element in the sequence, even through pointer arithmetics, and provides relatively fast addition/removal of elements at the end of the sequence.
Allocator-aware
The container uses an allocator object to dynamically handle its storage needs.

Template parameters

T
Type of the elements.
Only if T is guaranteed to not throw while moving, implementations can optimize to move elements instead of copying them during reallocations.
Aliased as member type vector::value_type.
Alloc
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 vector::allocator_type.

Member types

member typedefinitionnotes
value_typeThe first template parameter (T)
allocator_typeThe second template parameter (Alloc)defaults to: allocator<value_type>
referenceallocator_type::referencefor the default allocator: value_type&
const_referenceallocator_type::const_referencefor the default allocator: const value_type&
pointerallocator_type::pointerfor the default allocator: value_type*
const_pointerallocator_type::const_pointerfor the default allocator: const value_type*
iteratora random access iterator to value_typeconvertible to const_iterator
const_iteratora random access iterator to const value_type
reverse_iteratorreverse_iterator<iterator>
const_reverse_iteratorreverse_iterator<const_iterator>
difference_typea signed integral type, identical to: iterator_traits<iterator>::difference_typeusually the same as ptrdiff_t
size_typean unsigned integral type that can represent any non-negative value of difference_typeusually the same as size_t
member typedefinitionnotes
value_typeThe first template parameter (T)
allocator_typeThe second template parameter (Alloc)defaults to: allocator<value_type>
referencevalue_type&
const_referenceconst value_type&
pointerallocator_traits<allocator_type>::pointerfor the default allocator: value_type*
const_pointerallocator_traits<allocator_type>::const_pointerfor the default allocator: const value_type*
iteratora random access iterator to value_typeconvertible to const_iterator
const_iteratora random access iterator to const value_type
reverse_iteratorreverse_iterator<iterator>
const_reverse_iteratorreverse_iterator<const_iterator>
difference_typea signed integral type, identical to:
iterator_traits<iterator>::difference_type
usually the same as ptrdiff_t
size_typean unsigned integral type that can represent any non-negative value of difference_typeusually the same as size_t

Member functions


Iterators:

Capacity:

Element access:

Modifiers:

Allocator:

Non-member function overloads


Template specializations

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