std::span
<span> 에 정의되어 있음. | ||
template< class T, | (since C++20) | |
The class template span describes an object that can refer to a contiguous sequence of objects with the first element of the sequence at position zero. A span can either have a static extent, in which case the number of elements in the sequence is known at compile-time and encoded in the type, or a dynamic extent.
If a span has dynamic extent a typical implementation holds two members: a pointer to T and a size. A span with static extent may have only one member: a pointer to T.
Every specialization of | (since C++23) |
목차 |
[편집]Template parameters
| T | - | element type; must be a complete object type that is not an abstract class type |
| Extent | - | the number of elements in the sequence, or std::dynamic_extent if dynamic |
[편집]Member types
| Member type | Definition |
element_type | T |
value_type | std::remove_cv_t<T> |
size_type | std::size_t |
difference_type | std::ptrdiff_t |
pointer | T* |
const_pointer | const T* |
reference | T& |
const_reference | const T& |
iterator | implementation-defined LegacyRandomAccessIterator, ConstexprIterator, and contiguous_iterator whose value_type is value_type |
reverse_iterator | std::reverse_iterator<iterator> |
Note: iterator is a mutable iterator if T is not const-qualified.
All requirements on the iterator types of a Container apply to the iterator type of span as well.
[편집]Member constant
staticconstexprstd::size_t extent = Extent; | ||
[편집]Member functions
span 을 생성합니다 (public member function) | |
span을 할당합니다 (public member function) | |
Iterators | |
| 첫번째 원소로의 반복자(iterator)를 반환한다. (public member function) | |
| 마지막 원소로의 반복자(iterator)를 반환한다. (public member function) | |
| 첫번째 원소로의 역방향 반복자(reverse iterator)를 반환한다. (public member function) | |
| 마지막 원소로의 역방향 반복자(reverse iterator)를 반환한다. (public member function) | |
Element access | |
| 첫번째 요소에 접근한다. (public member function) | |
| 마지막 요소에 접근한다. (public member function) | |
| 연속체의 요소에 접근합니다 (public member function) | |
| 연속체의 시작 지점 포인터를 반환합니다 (public member function) | |
Observers | |
| 연속체 안의 요소 개수를 반환합니다 (public member function) | |
| 연속체의 크기를 바이트(byte) 단위값으로 반환합니다 (public member function) | |
| 연속체가 비어있는지 검사합니다 (public member function) | |
Subviews | |
| 연속체의 첫 N개의 요소를 담은 span을 획득합니다 (public member function) | |
| 연속체의 마지막 N개의 요소를 담은 span 을 획득합니다 (public member function) | |
| span의 하위span을 획득합니다 (public member function) | |
[편집]Non-member functions
(C++20) | span 을 하위 byte데이터에 대한 보기(view)로 변환합니다 (function template) |
[편집]Non-member constant
(C++20) | span이 동적 크기임을 나타내는 size_t 타입의 상수 (constant) |
[편집]Helper templates
template<class T, std::size_t Extent> inlineconstexprbool ranges::enable_borrowed_range<std::span<T, Extent>>=true; | ||
This specialization of ranges::enable_borrowed_range makes span satisfy borrowed_range.
template<class T, std::size_t Extent> inlineconstexprbool ranges::enable_view<std::span<T, Extent>>=true; | ||
This specialization of ranges::enable_view makes span satisfy view.
[편집]Deduction guides
[편집]Notes
Specializations of std::span are already trivially copyable types in all existing implementations, even before the formal requirement introduced in C++23.
[편집]Example
The example uses std::span to implement some algorithms on contiguous ranges.
#include <algorithm>#include <cstddef>#include <iostream>#include <span> template<class T, std::size_t N>[[nodiscard]]constexprauto slide(std::span<T,N> s, std::size_t offset, std::size_t width){return s.subspan(offset, offset + width <= s.size()? width : 0U);} template<class T, std::size_t N, std::size_t M>[[nodiscard]]constexprbool starts_with(std::span<T,N> data, std::span<T,M> prefix){return data.size()>= prefix.size()&&std::equal(prefix.begin(), prefix.end(), data.begin());} template<class T, std::size_t N, std::size_t M>[[nodiscard]]constexprbool ends_with(std::span<T,N> data, std::span<T,M> suffix){return data.size()>= suffix.size()&&std::equal(data.end()- suffix.size(), data.end(), suffix.end()- suffix.size());} template<class T, std::size_t N, std::size_t M>[[nodiscard]]constexprbool contains(std::span<T,N> span, std::span<T,M> sub){returnstd::search(span.begin(), span.end(), sub.begin(), sub.end())!= span.end();// return std::ranges::search(span, sub).begin() != span.end();} void print(constauto& seq){for(constauto& elem : seq)std::cout<< elem <<' ';std::cout<<'\n';} int main(){constexprint a[]{0, 1, 2, 3, 4, 5, 6, 7, 8};constexprint b[]{8, 7, 6}; for(std::size_t offset{};;++offset){constexprstd::size_t width{6};auto s = slide(std::span{a}, offset, width);if(s.empty())break; print(s);} static_assert(starts_with(std::span{a}, std::span{a,4})&& starts_with(std::span{a+1, 4}, std::span{a+1,3})&&!starts_with(std::span{a}, std::span{b})&&!starts_with(std::span{a,8}, std::span{a+1,3})&& ends_with(std::span{a}, std::span{a+6,3})&&!ends_with(std::span{a}, std::span{a+6,2})&& contains(std::span{a}, std::span{a+1,4})&&!contains(std::span{a,8}, std::span{a,9}));}
Output:
0 1 2 3 4 5 1 2 3 4 5 6 2 3 4 5 6 7 3 4 5 6 7 8
[편집]Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2325R3 | C++20 | span of non-zero static extents were not view | they are as default_initializable is not required |
[편집]See also
(C++11) | allows the use of initializer list syntax to initialize non plain-old-data types (class template) |
(C++17) | 읽기 전용의 문자열 보기(view) (class template) |
(C++20) | combines an iterator-sentinel pair into a view(class template) |
