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Introduction
Vectors are sequence container that can change size. Container is a objects that hold data of same type. Sequence containers store elements strictly in linear sequence.
Vector stores elements in contiguous memory locations and enables direct access to any element using subscript operator []. Unlike array, vector can shrink or expand as needed at run time. The storage of the vector is handled automatically.
To support shrink and expand functionality at runtime, vector container may allocate some extra storage to accommodate for possible growth thus container have actual capacity greater than the size. Therefore, compared to array, vector consumes more memory in exchange for the ability to manage storage and grow dynamically in an efficient way.
Zero sized vectors are also valid. In that case vector.begin() and vector.end() points to same location. But behavior of calling front() or back() is undefined.
Definition
Below is definition of std::vector from <vector> header file
template < class T, class Alloc = allocator<T> > class vector;
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 <vector>
Below is list of all methods from <vector> header.
Constructors
| Sr.No. | Method & Description |
|---|---|
| 1 | vector::vector default constructor
Constructs an empty container, with zero elements. |
| 2 | vector::vector fill constructor
Constructs a container with n elements and assignd val to each element. |
| 3 | vector::vector range constructor
Constructs a container with as many elements in range of first to last. |
| 4 | vector::vector copy constructor
Constructs a container with copy of each elements present in existing container x. |
| 5 | vector::vector move constructor
Constructs the container with the contents of other using move semantics. |
| 6 | vector::vector initializer list constructor
Constructs a container from initializer list. |
Destructor
| Sr.No. | Method & Description |
|---|---|
| 1 | vector::~vector
Destroys container by deallocating container memory. |
Member functions
| Sr.No. | Method & Description |
|---|---|
| 1 | vector::assign fill version
Assign new values to the vector elements by replacing old ones. |
| 2 | vector::assign range version
Assign new values to the vector elements by replacing old ones. |
| 3 | vector::assign initializer list version
Assign new values to the vector elements by replacing old ones. |
| 4 | vector::at
Returns reference to the element present at location n in the vector. |
| 5 | vector::back
Returns a reference to the last element of the vector. |
| 6 | vector::begin
Return a random access iterator pointing to the first element of the vector. |
| 7 | vector::capacity
Returns the size of allocate storage, expressed in terms of elements. |
| 8 | vector::cbegin
Returns a constant random access iterator which points to the beginning of the vector. |
| 9 | vector::cend
Returns a constant random access iterator which points to the beginning of the vector. |
| 10 | vector::clear
Destroys the vector by removing all elements from the vector and sets size of vector to zero. |
| 11 | vector::crbegin
Returns a constant reverse iterator which points to the reverser beginning of the container. |
| 12 | vector::crend
Returns a constant reverse iterator which points to the reverse end of the vector. |
| 13 | vector::data
Returns a pointer to the first element of the vector container. |
| 14 | vector::emplace
Extends container by inserting new element at position. |
| 15 | vector::emplace_back
Inserts new element at the end of vector. |
| 16 | vector::empty
Tests whether vector is empty or not. |
| 17 | vector::end
Returns an iterator which points to past-the-end element in the vector container. |
| 18 | vector::erase position version
Removes single element from the the vector. |
| 19 | vector::erase range version
Removes single element from the the vector. |
| 20 | vector::front
Returns a reference to the first element of the vector. |
| 21 | vector::get_allocator
Returns an allocator associated with vector. |
| 22 | vector::insert single element version
Extends iterator by inserting new element at position. |
| 23 | vector::insert fill version
Extends vector by inserting new element in the container. |
| 24 | vector::insert range version
Extends vector by inserting new element in the container. |
| 25 | vector::insert move version
Extends vector by inserting new element in the container. |
| 26 | vector::insert initializer list version
Extends vector by inserting new element in the container. |
| 27 | vector::max_size
Returns the maximum number of elements can be held by vector. |
| 28 | vector::operator= copy version
Assign new contents to the vector by replacing old ones and modifies size if necessary. |
| 29 | vector::operator= move version
Assign new contents to the vector by replacing old ones and modifies size if necessary. |
| 30 | vector::operator = initializer list version
Assign new contents to the vector by replacing old ones and modifies size if necessary. |
| 31 | vector::operator[]
Returns a reference to the element present at location n. |
| 32 | vector::pop_back
Removes last element from vector and reduces size of vector by one. |
| 33 | vector::push_back
Inserts new element at the end of vector and increases size of vector by one. |
| 34 | vector::rbegin
Returns a reverse iterator which points to the last element of the vector. |
| 35 | vector::rend
Returns a reverse iterator which points to the reverse end of the vector. |
| 36 | vector::reserve
Requests to reserve vector capacity be at least enough to contain n elements. |
| 37 | vector::resize
Changes the size of vector. |
| 38 | vector::shrink_to_fit
Requests the container to reduce it”s capacity to fit its size. |
| 39 | vector::size
Returns the number of elements present in the vector. |
| 40 | vector::swap
Exchanges the content of vector with contents of vector x. |
Non-member overloaded functions
| Sr.No. | Method & Description |
|---|---|
| 1 | operator ==
Tests whether two vectors are equal or not. |
| 2 | operator !=
Tests whether two vectors are equal or not. |
| 3 | operator <
Tests whether first vector is less than other or not. |
| 4 | operator <=
Tests whether first vector is less than or equal to other or not. |
| 5 | operator >
Tests whether first vector is greater than other or not. |
| 6 | operator >=
Tests whether first vector is greater than or equal to other or not. |
| 7 | swap
Exchanges the contents of two vector. |
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