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

 

C++

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Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

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Containers library

Iterators library

Ranges library (C++20)

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Numerics library

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Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

Views

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 > explicit(extent != std::dynamic_extent) constexpr span( It first, size_type count );	(2)
template< class It, class End > explicit(extent != std::dynamic_extent) constexpr span( It first, End last );	(3)
template< std::size_t N > constexpr span( element_type (&arr)[N] ) noexcept;	(4)
template< class U, std::size_t N > constexpr span( std::array<U, N>& arr ) noexcept;	(5)
template< class U, std::size_t N > constexpr span( const std::array<U, N>& arr ) noexcept;	(6)
template< class R > explicit(extent != std::dynamic_extent) constexpr span( R&& range );	(7)
template< class U, std::size_t N > explicit(extent != std::dynamic_extent && N == std::dynamic_extent) constexpr span( const std::span<U, N>& source ) 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 participates in overload resolution only 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.
• This overload participates in overload resolution only 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.
• This overload participates in overload resolution only 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
• std::is_convertible_v<End, std::size_t> is false.

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 participate in overload resolution only if extent == std::dynamic_extent || N == extent is true and the conversion from std::remove_pointer_t<decltype(data(arr))> to element_type is at most a qualification conversion. These constructor templates are never used for class template argument deduction.

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

• 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 or both extent != dynamic_extent and std::ranges::size(range) != extent are true.
• This overload participates in overload resolution only if

• 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 source; the resulting span has size() == source.size() and data() == source.data().

• The behavior is undefined if both extent != dynamic_extent and source.size() != extent are true.
• This overload participates in overload resolution only if at least one of extent == std::dynamic_extent, N == std::dynamic_extent and N == extent is true and the conversion from U to element_type is at most a qualification conversion.

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
range	-	range to construct a view for
source	-	another span to convert from
other	-	another span to copy from

Exceptions

2) Throws nothing.

3) Throws what and when last - 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)