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std::vector

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Defined in header <vector>
template<

    class T,
    class Allocator = std::allocator<T>

> class vector;

std::vector is a sequence container that encapsulates dynamic size arrays.

The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets on regular pointers to elements. This means that a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array.

The storage of the vector is handled automatically, being expanded and contracted as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using capacity() function. Extra memory can be returned to the system via a call to shrink_to_fit().

Reallocations are usually costly operations in terms of performance. reserve() function can be used to eliminate reallocations if the number of elements is known beforehand.

The complexity (efficiency) of common operations on vectors is as follows:

  • Random access - constant O(1)
  • Insertion or removal of elements at the end - amortized constant O(1)
  • Insertion or removal of elements - linear in distance to the end of the vector O(n)

std::vector meets the requirements of Container, AllocatorAwareContainer, SequenceContainer and ReversibleContainer.

Contents

Template parameters

T - The type of the elements.
T must meet the requirements of CopyAssignable and CopyConstructible. (until C++11)
The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type is a complete type and meets the requirements of MoveConstructible and MoveAssignable, but many member functions impose stricter requirements. (since C++11)

[edit]

Allocator - An allocator that is used to acquire memory to store the elements. The type must meet the requirements of Allocator. [edit]

Specializations

The standard library provides a specialization of std::vector for the type bool, which is optimized for space efficiency.

space-efficient dynamic bitset
(class template specialization) [edit]

Member types

Member type Definition
value_type T [edit]
allocator_type Allocator [edit]
size_type Unsigned integral type (usually std::size_t) [edit]
difference_type Signed integer type (usually std::ptrdiff_t) [edit]
reference
Allocator::reference (until C++11)
value_type& (since C++11)
[edit]
const_reference
Allocator::const_reference (until C++11)
const value_type& (since C++11)
[edit]
pointer
Allocator::pointer (until C++11)
std::allocator_traits<Allocator>::pointer (since C++11)
[edit]
const_pointer
Allocator::const_pointer (until C++11)
std::allocator_traits<Allocator>::const_pointer (since C++11)
[edit]
iterator RandomAccessIterator [edit]
const_iterator Constant random access iterator [edit]
reverse_iterator std::reverse_iterator<iterator> [edit]
const_reverse_iterator std::reverse_iterator<const_iterator> [edit]

Member functions

constructs the vector
(public member function) [edit]
destructs the vector
(public member function) [edit]
assigns values to the container
(public member function) [edit]
assigns values to the container
(public member function) [edit]
returns the associated allocator
(public member function) [edit]
Element access
access specified element with bounds checking
(public member function) [edit]
access specified element
(public member function) [edit]
access the first element
(public member function) [edit]
access the last element
(public member function) [edit]
(C++11)
direct access to the underlying array
(public member function) [edit]
Iterators
returns an iterator to the beginning
(public member function) [edit]
returns an iterator to the end
(public member function) [edit]
returns a reverse iterator to the beginning
(public member function) [edit]
returns a reverse iterator to the end
(public member function) [edit]
Capacity
checks whether the container is empty
(public member function) [edit]
returns the number of elements
(public member function) [edit]
returns the maximum possible number of elements
(public member function) [edit]
reserves storage
(public member function) [edit]
returns the number of elements that can be held in currently allocated storage
(public member function) [edit]
reduces memory usage by freeing unused memory
(public member function) [edit]
Modifiers
clears the contents
(public member function) [edit]
inserts elements
(public member function) [edit]
(C++11)
constructs element in-place
(public member function) [edit]
erases elements
(public member function) [edit]
adds elements to the end
(public member function) [edit]
constructs elements in-place at the end
(public member function) [edit]
removes the last element
(public member function) [edit]
changes the number of elements stored
(public member function) [edit]
swaps the contents
(public member function) [edit]

Non-member functions

lexicographically compares the values in the vector
(function template) [edit]
specializes the std::swap algorithm
(function template) [edit]