std::span<T,Extent>::span

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

span (C++20)

 

std::span

Member functions

span::span

span::operator=

Element access

span::front

span::back

span::operator[]

span::data

Iterators

span::begin

span::end

span::rbegin

span::rend

Observers

span::empty

span::size

span::size_bytes

Subviews

span::first

span::last

span::subspan

Non-member functions

as_bytesas_writable_bytes

Non-member constant

dynamic_extent

Deduction guides

 

constexpr span() noexcept;	(1)
template <class It> constexpr span(It first, size_type count);	(2)
template <class It, class End> constexpr span(It first, End last);	(3)
template <std::size_t N> constexpr span(element_type (&arr)[N]) noexcept;	(4)
template <std::size_t N> constexpr span(std::array<value_type, N>& arr) noexcept;	(5)
template <std::size_t N> constexpr span(const std::array<value_type, N>& arr) noexcept;	(6)
template <class R> constexpr span(R&& r);	(7)
template <class U, std::size_t N> constexpr span(const std::span<U, N>& s) noexcept;	(8)
constexpr span(const span& other) noexcept = default;	(9)

Constructs a span.

1) Constructs an empty span whose data() == nullptr and size() == 0. This overload only participates in overload resolution if extent == 0 || extent == std::dynamic_extent.

2) Constructs a span that is a view over the range [first, first + count); the resulting span has data() == std::to_address(first) and size() == count. The behavior is undefined if [first, first + count) is not a valid range, if It does not actually model contiguous_iterator, or if extent != std::dynamic_extent && count != extent. These overloads only participate in overload resolution if

• It satisfies contiguous_iterator
• the conversion from std::iter_reference_t<It> to element_type is at most a qualification conversion.

3) Constructs a span that is a view over the range [first, last); the resulting span has data() == std::to_address(first) and size() == last-first. The behavior is undefined if [first, last) is not a valid range, if It does not actually model contiguous_iterator, if End does not actually model sized_sentinel_for for It, or if extent != std::dynamic_extent && last-first != extent. These overloads only participate in overload resolution if

• It satisfies contiguous_iterator,
• End satisfies sized_sentinel_for for It,
• the conversion from std::iter_reference_t<It> to element_type is at most a qualification conversion, and
• End is not convertible to std::size_t.

4-6) Constructs a span that is a view over the array arr; the resulting span has size() == N and data() == std::data(arr). These overloads only participate in overload resolution if extent == std::dynamic_extent || N == extent is true and std::remove_pointer_t<decltype(std::data(arr))>(*)[] is convertible to element_type (*)[]

7) Constructs a span that is a view over the range r; the resulting span has size() == std::ranges::size(r) and data() == std::ranges::data(r).

The behavior is undefined if R does not actually model contiguous_range and sized_range or if R does not model borrowed_range while element_type is non-const. These overloads only participate in overload resolution if

• extent == dynamic_extent;
• R satisfies contiguous_range and sized_range,
• either R satisfies borrowed_range or std::is_const_v<element_type> is true
• std::remove_cvref_t<R> is not a specialization of std::span,
• std::remove_cvref_t<R> is not a specialization of std::array
• std::is_array_v<std::remove_cvref_t<R>> is false, and
• the conversion from std::ranges::range_reference_t<R> to element_type is at most a qualification conversion

8) Converting constructor from another span s; the resulting span has size() == s.size() and data() == s.data(). This overload only participates in overload resolution if extent == std::dynamic_extent || N == extent is true and U (*)[] is convertible to element_type (*)[].

9) Defaulted copy constructor copies the size and data pointer; the resulting span has size() == other.size() and data() == other.data().

Parameters

first	-	iterator to the first element of the sequence
count	-	number of elements in the sequence
last	-	iterator past the last element of the sequence or another sentinel
arr	-	array to construct a view for
r	-	range to construct a view for
s	-	another span to convert from
other	-	another span to copy from

Exceptions

2-3) Throws what and when std::to_address(first) throws.

7) Throws what and when std::ranges::size(r) and std::ranges::data(r) throw.

See also

data	returns a pointer to the beginning of the sequence of elements (public member function)
size	returns the number of elements in the sequence (public member function)
operator=	assigns a span (public member function)
sizessize (C++17)(C++20)	returns the size of a container or array (function template)
data (C++17)	obtains the pointer to the underlying array (function template)