The header <array> defines a class template for storing fixed-size
sequences of objects. An array supports random access iterators. An
instance of array<T, N> stores N elements of type T, so that
size() == N is an invariant. The elements of an array are stored contiguously,
meaning that if a is an array<T, N> then it obeys the identity
&a[n] == &a[0] + n for all 0 <= n < N.
An array is an aggregate ([dcl.init.aggr]) that can be initialized with the syntax
array<T, N> a = { initializer-list };
where initializer-list is a comma-separated list of up to N elements whose types are convertible to T.
An array satisfies all of the requirements of a container and of a reversible container ([container.requirements]), except that a default constructed array object is not empty and that swap does not have constant complexity. An array satisfies some of the requirements of a sequence container ([sequence.reqmts]). Descriptions are provided here only for operations on array that are not described in one of these tables and for operations where there is additional semantic information.
namespace std {
template <class T, size_t N>
struct array {
// types:
typedef T& reference;
typedef const T& const_reference;
typedef implementation-defined iterator;
typedef implementation-defined const_iterator;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef T value_type;
typedef T* pointer;
typedef const T* const_pointer;
typedef std::reverse_iterator<iterator> reverse_iterator;
typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
T elems[N]; // exposition only
// no explicit construct/copy/destroy for aggregate type
void fill(const T& u);
void swap(array&) noexcept(noexcept(swap(declval<T&>(), declval<T&>())));
// 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;
// capacity:
constexpr size_type size() const noexcept;
constexpr size_type max_size() const noexcept;
constexpr bool empty() const noexcept;
// element access:
reference operator[](size_type n);
constexpr const_reference operator[](size_type n) const;
reference at(size_type n);
constexpr const_reference at(size_type n) const;
reference front();
constexpr const_reference front() const;
reference back();
constexpr const_reference back() const;
T * data() noexcept;
const T * data() const noexcept;
};
}
[ Note: The member variable elems is shown for exposition only, to emphasize that array is a class aggregate. The name elems is not part of array's interface. — end note ]
The conditions for an aggregate ([dcl.init.aggr]) shall be met. Class array relies on the implicitly-declared special member functions ([class.ctor], [class.dtor], and [class.copy]) to conform to the container requirements table in [container.requirements]. In addition to the requirements specified in the container requirements table, the implicit move constructor and move assignment operator for array require that T be MoveConstructible or MoveAssignable, respectively.
template <class T, size_t N> void swap(array<T,N>& x, array<T,N>& y) noexcept(noexcept(x.swap(y)));
Effects:
x.swap(y);
Complexity: Linear in N.
template <class T, size_t N> constexpr size_type array<T,N>::size() const noexcept;
Returns: N
T* data() noexcept;
const T* data() const noexcept;
Returns: elems.
void swap(array& y) noexcept(noexcept(swap(declval<T&>(), declval<T&>())));
Effects: swap_ranges(begin(), end(), y.begin())
Throws: Nothing unless one of the element-wise swap calls throws an exception.
Note: Unlike the swap function for other containers, array::swap takes linear time, may exit via an exception, and does not cause iterators to become associated with the other container.
array shall provide support for the special case N == 0.
In the case that N == 0, begin() == end() == unique value. The return value of data() is unspecified.
The effect of calling front() or back() for a zero-sized array is undefined.
Member function swap() shall have a noexcept-specification which is equivalent to noexcept(true).
template <class T, size_t N>
struct tuple_size<array<T, N>>
: integral_constant<size_t, N> { };
tuple_element<I, array<T, N> >::type
Requires: I < N. The program is ill-formed if I is out of bounds.
Value: The type T.
template <size_t I, class T, size_t N>
constexpr T& get(array<T, N>& a) noexcept;
Requires: I < N. The program is ill-formed if I is out of bounds.
Returns: A reference to the Ith element of a, where indexing is zero-based.
template <size_t I, class T, size_t N>
constexpr T&& get(array<T, N>&& a) noexcept;
Effects: Equivalent to return std::move(get<I>(a));
template <size_t I, class T, size_t N>
constexpr const T& get(const array<T, N>& a) noexcept;
Requires: I < N. The program is ill-formed if I is out of bounds.
Returns: A const reference to the Ith element of a, where indexing is zero-based.