标准库标头 <span> (C++20)
来自cppreference.com
此头文件是容器库的一部分。
类 | |
(C++20) |
连续的对象序列上的无所有权视图 (类模板) |
常量 | |
(C++20) |
std::size_t 类型的常量，指明 span 拥有动态长度 (常量) |
函数 | |
(C++20) |
转换 span 为对其底层字节的视图 (函数模板) |
范围访问 | |
(C++11)(C++14) |
返回指向容器或数组起始的迭代器 (函数模板) |
(C++11)(C++14) |
返回指向容器或数组结尾的迭代器 (函数模板) |
(C++14) |
返回指向一个容器或数组的逆向迭代器 (函数模板) |
(C++14) |
返回容器或数组的逆向尾迭代器 (函数模板) |
(C++17)(C++20) |
返回容器或数组的大小 (函数模板) |
(C++17) |
检查容器是否为空 (函数模板) |
(C++17) |
获得指向底层数组的指针 (函数模板) |
概要
#include <initializer_list>
// 大多数为独立
namespace std {
// 常量
inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
template<class T>
concept /*integral-constant-like*/ = // 仅用于阐释
is_integral_v<decltype(T::value)> &&
!is_same_v<bool, remove_const_t<decltype(T::value)>> &&
convertible_to<T, decltype(T::value)> &&
equality_comparable_with<T, decltype(T::value)> &&
bool_constant<T() == T::value>::value &&
bool_constant<static_cast<decltype(T::value)>(T()) == T::value>::value;
template<class T>
constexpr size_t /*maybe-static-ext*/ = dynamic_extent; // 仅用于阐释
template</*integral-constant-like*/ T>
constexpr size_t /*maybe-static-ext*/<T> = { T::value };
// 类模板 span
template<class ElementType, size_t Extent = dynamic_extent>
class span; // 部分独立
template<class ElementType, size_t Extent>
constexpr bool ranges::enable_view<span<ElementType, Extent>> = true;
template<class ElementType, size_t Extent>
constexpr bool ranges::enable_borrowed_range<span<ElementType, Extent>> = true;
// 对象表示的视图
template<class ElementType, size_t Extent>
span<const byte,
Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
as_bytes(span<ElementType, Extent> s) noexcept;
template<class ElementType, size_t Extent>
span<byte, Extent == dynamic_extent ? dynamic_extent : sizeof(ElementType) * Extent>
as_writable_bytes(span<ElementType, Extent> s) noexcept;
}
类模板 std::span
namespace std {
template<class ElementType, size_t Extent = dynamic_extent>
class span
{
public:
// 常量与类型
using element_type = ElementType;
using value_type = remove_cv_t<ElementType>;
using size_type = size_t;
using difference_type = ptrdiff_t;
using pointer = element_type*;
using const_pointer = const element_type*;
using reference = element_type&;
using const_reference = const element_type&;
using iterator = /* 由实现定义 */;
using const_iterator = std::const_iterator<iterator>;
using reverse_iterator = std::reverse_iterator<iterator>;
using const_reverse_iterator = std::const_iterator<reverse_iterator>;
static constexpr size_type extent = Extent;
// 构造函数、复制与赋值
constexpr span() noexcept;
template<class It>
constexpr explicit(extent != dynamic_extent) span(It first, size_type count);
template<class It, class End>
constexpr explicit(extent != dynamic_extent) span(It first, End last);
template<size_t N>
constexpr span(type_identity_t<element_type> (&arr)[N]) noexcept;
template<class T, size_t N>
constexpr span(array<T, N>& arr) noexcept;
template<class T, size_t N>
constexpr span(const array<T, N>& arr) noexcept;
template<class R>
constexpr explicit(extent != dynamic_extent) span(R&& r);
constexpr explicit(extent != dynamic_extent)
span(std::initializer_list<value_type> il);
constexpr span(const span& other) noexcept = default;
template<class OtherElementType, size_t OtherExtent>
constexpr explicit(/* see description */)
span(const span<OtherElementType, OtherExtent>& s) noexcept;
constexpr span& operator=(const span& other) noexcept = default;
// 子视图
template<size_t Count>
constexpr span<element_type, Count> first() const;
template<size_t Count>
constexpr span<element_type, Count> last() const;
template<size_t Offset, size_t Count = dynamic_extent>
constexpr span<element_type, /* see description */> subspan() const;
constexpr span<element_type, dynamic_extent> first(size_type count) const;
constexpr span<element_type, dynamic_extent> last(size_type count) const;
constexpr span<element_type, dynamic_extent> subspan(
size_type offset,
size_type count = dynamic_extent) const;
// 观察器
constexpr size_type size() const noexcept;
constexpr size_type size_bytes() const noexcept;
constexpr bool empty() const noexcept;
// 元素访问
constexpr reference operator[](size_type idx) const;
constexpr reference at(size_type idx) const; // 独立环境中删除
constexpr reference front() const;
constexpr reference back() const;
constexpr pointer data() const noexcept;
// 迭代器支持
constexpr iterator begin() const noexcept;
constexpr iterator end() const noexcept;
constexpr const_iterator cbegin() const noexcept { return begin(); }
constexpr const_iterator cend() const noexcept { return end(); }
constexpr reverse_iterator rbegin() const noexcept;
constexpr reverse_iterator rend() const noexcept;
constexpr const_reverse_iterator crbegin() const noexcept { return rbegin(); }
constexpr const_reverse_iterator crend() const noexcept { return rend(); }
private:
pointer /*data_*/; // 仅用于阐述
size_type /*size_*/; // 仅用于阐述
};
template<class It, class EndOrSize>
span(It, EndOrSize)
-> span<remove_reference_t<iter_reference_t<It>>, /*maybe-static-ext*/<EndOrSize>>;
template<class T, size_t N>
span(T (&)[N]) -> span<T, N>;
template<class T, size_t N>
span(array<T, N>&) -> span<T, N>;
template<class T, size_t N>
span(const array<T, N>&) -> span<const T, N>;
template<class R>
span(R&&) -> span<remove_reference_t<ranges::range_reference_t<R>>>;
}