23 Containers library [containers]

23.3 Sequence containers [sequences]

23.3.3 Class template array [array]

23.3.3.1 Overview [array.overview]

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The header <array> defines a class template for storing fixed-size sequences of objects.
An array is a contiguous container.
An instance of array<T, N> stores N elements of type T, so that size() == N is an invariant.
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An array is an aggregate that can be list-initialized with up to N elements whose types are convertible to T.
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An array meets all of the requirements of a container ([container.reqmts]) and of a reversible container ([container.rev.reqmts]), except that a default constructed array object is not empty if .
An array meets some of the requirements of a sequence container.
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.
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array<T, N> is a structural type ([temp.param]) if T is a structural type.
Two values a1 and a2 of type array<T, N> are template-argument-equivalent if and only if each pair of corresponding elements in a1 and a2 are template-argument-equivalent.
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The types iterator and const_iterator meet the constexpr iterator requirements.
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namespace std { template<class T, size_t N> struct array { // types using value_type = T; using pointer = T*; using const_pointer = const T*; using reference = T&; using const_reference = const T&; using size_type = size_t; using difference_type = ptrdiff_t; 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>; // no explicit construct/copy/destroy for aggregate type constexpr void fill(const T& u); constexpr void swap(array&) noexcept(is_nothrow_swappable_v<T>); // iterators constexpr iterator begin() noexcept; constexpr const_iterator begin() const noexcept; constexpr iterator end() noexcept; constexpr const_iterator end() const noexcept; constexpr reverse_iterator rbegin() noexcept; constexpr const_reverse_iterator rbegin() const noexcept; constexpr reverse_iterator rend() noexcept; constexpr const_reverse_iterator rend() const noexcept; constexpr const_iterator cbegin() const noexcept; constexpr const_iterator cend() const noexcept; constexpr const_reverse_iterator crbegin() const noexcept; constexpr const_reverse_iterator crend() const noexcept; // capacity constexpr bool empty() const noexcept; constexpr size_type size() const noexcept; constexpr size_type max_size() const noexcept; // element access constexpr reference operator[](size_type n); constexpr const_reference operator[](size_type n) const; constexpr reference at(size_type n); // freestanding-deleted constexpr const_reference at(size_type n) const; // freestanding-deleted constexpr reference front(); constexpr const_reference front() const; constexpr reference back(); constexpr const_reference back() const; constexpr T * data() noexcept; constexpr const T * data() const noexcept; }; template<class T, class... U> array(T, U...) -> array<T, 1 + sizeof...(U)>; }

23.3.3.2 Constructors, copy, and assignment [array.cons]

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An array relies on the implicitly-declared special member functions ([class.default.ctor], [class.dtor], [class.copy.ctor]) to conform to the container requirements table in [container.requirements].
In addition to the requirements specified in the container requirements table, the implicitly-declared move constructor and move assignment operator for array require that T be Cpp17MoveConstructible or Cpp17MoveAssignable, respectively.
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template<class T, class... U> array(T, U...) -> array<T, 1 + sizeof...(U)>;
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Mandates: (is_same_v<T, U> && ...) is true.

23.3.3.3 Member functions [array.members]

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constexpr size_type size() const noexcept;
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Returns: N.
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constexpr T* data() noexcept; constexpr const T* data() const noexcept;
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Returns: A pointer such that [data(), data() + size()) is a valid range.
For a non-empty array, data() == addressof(front()) is true.
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constexpr void fill(const T& u);
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Effects: As if by fill_n(begin(), N, u).
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constexpr void swap(array& y) noexcept(is_nothrow_swappable_v<T>);
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Effects: Equivalent to swap_ranges(begin(), end(), y.begin()).
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[Note 1: 
Unlike the swap function for other containers, array​::​swap takes linear time, can exit via an exception, and does not cause iterators to become associated with the other container.
— end note]

23.3.3.4 Specialized algorithms [array.special]

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template<class T, size_t N> constexpr void swap(array<T, N>& x, array<T, N>& y) noexcept(noexcept(x.swap(y)));
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Constraints: N == 0 or is_swappable_v<T> is true.
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Effects: As if by x.swap(y).
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Complexity: Linear in N.

23.3.3.5 Zero-sized arrays [array.zero]

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array shall provide support for the special case N == 0.
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In the case that N == 0, begin() == end() == unique value.
The return value of data() is unspecified.
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The effect of calling front() or back() for a zero-sized array is undefined.
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Member function swap() shall have a non-throwing exception specification.

23.3.3.6 Array creation functions [array.creation]

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template<class T, size_t N> constexpr array<remove_cv_t<T>, N> to_array(T (&a)[N]);
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Mandates: is_array_v<T> is false and is_constructible_v<remove_cv_t<T>, T&> is true.
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Preconditions: T meets the Cpp17CopyConstructible requirements.
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Returns: {{ a[0], …, a[N - 1] }}.
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template<class T, size_t N> constexpr array<remove_cv_t<T>, N> to_array(T (&&a)[N]);
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Mandates: is_array_v<T> is false and is_constructible_v<remove_cv_t<T>, T> is true.
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Preconditions: T meets the Cpp17MoveConstructible requirements.
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Returns: {{ std​::​move(a[0]), …, std​::​move(a[N - 1]) }}.

23.3.3.7 Tuple interface [array.tuple]

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template<class T, size_t N> struct tuple_size<array<T, N>> : integral_constant<size_t, N> { };
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template<size_t I, class T, size_t N> struct tuple_element<I, array<T, N>> { using type = T; };
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Mandates: I < N is true.
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template<size_t I, class T, size_t N> constexpr T& get(array<T, N>& a) noexcept; template<size_t I, class T, size_t N> constexpr T&& get(array<T, N>&& a) noexcept; template<size_t I, class T, size_t N> constexpr const T& get(const array<T, N>& a) noexcept; template<size_t I, class T, size_t N> constexpr const T&& get(const array<T, N>&& a) noexcept;
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Mandates: I < N is true.
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Returns: A reference to the element of a, where indexing is zero-based.