A vector is a sequence container that supports (amortized) constant time insert and erase operations at the end; insert and erase in the middle take linear time. Storage management is handled automatically, though hints can be given to improve efficiency.
A vector satisfies all of the requirements of a container and of a reversible container, of a sequence container, including most of the optional sequence container requirements, of an allocator-aware container, and, for an element type other than bool, of a contiguous container. The exceptions are the push_front, pop_front, and emplace_front member functions, which are not provided. Descriptions are provided here only for operations on vector that are not described in one of these tables or for operations where there is additional semantic information.
namespace std {
template <class T, class Allocator = allocator<T>>
class vector {
public:
// types:
using value_type = T;
using allocator_type = Allocator;
using pointer = typename allocator_traits<Allocator>::pointer;
using const_pointer = typename allocator_traits<Allocator>::const_pointer;
using reference = value_type&;
using const_reference = const value_type&;
using size_type = implementation-defined; // see [container.requirements]
using difference_type = implementation-defined; // see [container.requirements]
using iterator = implementation-defined; // see [container.requirements]
using const_iterator = implementation-defined; // see [container.requirements]
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
// [vector.cons], construct/copy/destroy
vector() noexcept(noexcept(Allocator())) : vector(Allocator()) { }
explicit vector(const Allocator&) noexcept;
explicit vector(size_type n, const Allocator& = Allocator());
vector(size_type n, const T& value, const Allocator& = Allocator());
template <class InputIterator>
vector(InputIterator first, InputIterator last, const Allocator& = Allocator());
vector(const vector& x);
vector(vector&&) noexcept;
vector(const vector&, const Allocator&);
vector(vector&&, const Allocator&);
vector(initializer_list<T>, const Allocator& = Allocator());
~vector();
vector& operator=(const vector& x);
vector& operator=(vector&& x)
noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
allocator_traits<Allocator>::is_always_equal::value);
vector& operator=(initializer_list<T>);
template <class InputIterator>
void assign(InputIterator first, InputIterator last);
void assign(size_type n, const T& u);
void assign(initializer_list<T>);
allocator_type get_allocator() const noexcept;
// iterators:
iterator begin() noexcept;
const_iterator begin() const noexcept;
iterator end() noexcept;
const_iterator end() const noexcept;
reverse_iterator rbegin() noexcept;
const_reverse_iterator rbegin() const noexcept;
reverse_iterator rend() noexcept;
const_reverse_iterator rend() const noexcept;
const_iterator cbegin() const noexcept;
const_iterator cend() const noexcept;
const_reverse_iterator crbegin() const noexcept;
const_reverse_iterator crend() const noexcept;
// [vector.capacity], capacity
bool empty() const noexcept;
size_type size() const noexcept;
size_type max_size() const noexcept;
size_type capacity() const noexcept;
void resize(size_type sz);
void resize(size_type sz, const T& c);
void reserve(size_type n);
void shrink_to_fit();
// element access:
reference operator[](size_type n);
const_reference operator[](size_type n) const;
const_reference at(size_type n) const;
reference at(size_type n);
reference front();
const_reference front() const;
reference back();
const_reference back() const;
// [vector.data], data access
T* data() noexcept;
const T* data() const noexcept;
// [vector.modifiers], modifiers
template <class... Args> reference emplace_back(Args&&... args);
void push_back(const T& x);
void push_back(T&& x);
void pop_back();
template <class... Args> iterator emplace(const_iterator position, Args&&... args);
iterator insert(const_iterator position, const T& x);
iterator insert(const_iterator position, T&& x);
iterator insert(const_iterator position, size_type n, const T& x);
template <class InputIterator>
iterator insert(const_iterator position, InputIterator first, InputIterator last);
iterator insert(const_iterator position, initializer_list<T> il);
iterator erase(const_iterator position);
iterator erase(const_iterator first, const_iterator last);
void swap(vector&)
noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
allocator_traits<Allocator>::is_always_equal::value);
void clear() noexcept;
};
template<class InputIterator,
class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
vector(InputIterator, InputIterator, Allocator = Allocator())
-> vector<typename iterator_traits<InputIterator>::value_type, Allocator>;
template <class T, class Allocator>
bool operator==(const vector<T, Allocator>& x, const vector<T, Allocator>& y);
template <class T, class Allocator>
bool operator< (const vector<T, Allocator>& x, const vector<T, Allocator>& y);
template <class T, class Allocator>
bool operator!=(const vector<T, Allocator>& x, const vector<T, Allocator>& y);
template <class T, class Allocator>
bool operator> (const vector<T, Allocator>& x, const vector<T, Allocator>& y);
template <class T, class Allocator>
bool operator>=(const vector<T, Allocator>& x, const vector<T, Allocator>& y);
template <class T, class Allocator>
bool operator<=(const vector<T, Allocator>& x, const vector<T, Allocator>& y);
// [vector.special], specialized algorithms
template <class T, class Allocator>
void swap(vector<T, Allocator>& x, vector<T, Allocator>& y)
noexcept(noexcept(x.swap(y)));
}An incomplete type T may be used when instantiating vector if the allocator satisfies the allocator completeness requirements. T shall be complete before any member of the resulting specialization of vector is referenced.
explicit vector(const Allocator&);
explicit vector(size_type n, const Allocator& = Allocator());
vector(size_type n, const T& value,
const Allocator& = Allocator());
template <class InputIterator>
vector(InputIterator first, InputIterator last,
const Allocator& = Allocator());
Complexity: Makes only N calls to the copy constructor of T (where N is the distance between first and last) and no reallocations if iterators first and last are of forward, bidirectional, or random access categories. It makes order N calls to the copy constructor of T and order logN reallocations if they are just input iterators.
size_type capacity() const noexcept;
void reserve(size_type n);
Effects: A directive that informs a vector of a planned change in size, so that it can manage the storage allocation accordingly. After reserve(), capacity() is greater or equal to the argument of reserve if reallocation happens; and equal to the previous value of capacity() otherwise. Reallocation happens at this point if and only if the current capacity is less than the argument of reserve(). If an exception is thrown other than by the move constructor of a non-CopyInsertable type, there are no effects.
Complexity: It does not change the size of the sequence and takes at most linear time in the size of the sequence.
Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence. No reallocation shall take place during insertions that happen after a call to reserve() until the time when an insertion would make the size of the vector greater than the value of capacity().
void shrink_to_fit();
Effects: shrink_to_fit is a non-binding request to reduce capacity() to size(). [ Note: The request is non-binding to allow latitude for implementation-specific optimizations. — end note ] It does not increase capacity(), but may reduce capacity() by causing reallocation. If an exception is thrown other than by the move constructor of a non-CopyInsertable T there are no effects.
Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence as well as the past-the-end iterator. If no reallocation happens, they remain valid.
void swap(vector& x)
noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
allocator_traits<Allocator>::is_always_equal::value);
void resize(size_type sz);
Effects: If sz < size(), erases the last size() - sz elements from the sequence. Otherwise, appends sz - size() default-inserted elements to the sequence.
Remarks: If an exception is thrown other than by the move constructor of a non-CopyInsertable T there are no effects.
void resize(size_type sz, const T& c);
Effects: If sz < size(), erases the last size() - sz elements from the sequence. Otherwise, appends sz - size() copies of c to the sequence.
reserve() uses Allocator::allocate() which may throw an appropriate exception.
T* data() noexcept;
const T* data() const noexcept;
Returns: A pointer such that [data(), data() + size()) is a valid range. For a non-empty vector, data() == addressof(front()).
iterator insert(const_iterator position, const T& x);
iterator insert(const_iterator position, T&& x);
iterator insert(const_iterator position, size_type n, const T& x);
template <class InputIterator>
iterator insert(const_iterator position, InputIterator first, InputIterator last);
iterator insert(const_iterator position, initializer_list<T>);
template <class... Args> reference emplace_back(Args&&... args);
template <class... Args> iterator emplace(const_iterator position, Args&&... args);
void push_back(const T& x);
void push_back(T&& x);
Remarks: Causes reallocation if the new size is greater than the old capacity. Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence. If no reallocation happens, all the iterators and references before the insertion point remain valid. If an exception is thrown other than by the copy constructor, move constructor, assignment operator, or move assignment operator of T or by any InputIterator operation there are no effects. If an exception is thrown while inserting a single element at the end and T is CopyInsertable or is_nothrow_move_constructible_v<T> is true, there are no effects. Otherwise, if an exception is thrown by the move constructor of a non-CopyInsertable T, the effects are unspecified.
Complexity: The complexity is linear in the number of elements inserted plus the distance to the end of the vector.
iterator erase(const_iterator position);
iterator erase(const_iterator first, const_iterator last);
void pop_back();
Complexity: The destructor of T is called the number of times equal to the number of the elements erased, but the assignment operator of T is called the number of times equal to the number of elements in the vector after the erased elements.
template <class T, class Allocator>
void swap(vector<T, Allocator>& x, vector<T, Allocator>& y)
noexcept(noexcept(x.swap(y)));