std::span<T,Extent>::span
From cppreference.com
| constexpr span() noexcept; |
(1) | (since C++20) |
| template< class It > explicit(extent != std::dynamic_extent) |
(2) | (since C++20) |
| template< class It, class End > explicit(extent != std::dynamic_extent) |
(3) | (since C++20) |
| template< std::size_t N > constexpr span( std::type_identity_t<element_type> (&arr)[N] ) noexcept; |
(4) | (since C++20) |
| template< class U, std::size_t N > constexpr span( std::array<U, N>& arr ) noexcept; |
(5) | (since C++20) |
| template< class U, std::size_t N > constexpr span( const std::array<U, N>& arr ) noexcept; |
(6) | (since C++20) |
| template< class R > explicit(extent != std::dynamic_extent) |
(7) | (since C++20) |
explicit(extent != std::dynamic_extent) constexpr span( std::initializer_list<value_type> il ) noexcept; |
(8) | (since C++26) |
| template< class U, std::size_t N > explicit(extent != std::dynamic_extent && N == std::dynamic_extent) |
(9) | (since C++20) |
| constexpr span( const span& other ) noexcept = default; |
(10) | (since C++20) |
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, ifItdoes not actually modelcontiguous_iterator, or if extent != std::dynamic_extent && count != extent. - This overload participates in overload resolution only if
Itsatisfiescontiguous_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, ifItdoes not actually modelcontiguous_iterator, ifEnddoes not actually modelsized_sentinel_forforIt, or if extent != std::dynamic_extent && last-first != extent. - This overload participates in overload resolution only if
-
Itsatisfiescontiguous_iterator, -
Endsatisfiessized_sentinel_forforIt, - 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.
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
Rdoes not actually modelcontiguous_rangeandsized_rangeor ifRdoes not modelborrowed_rangewhile 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
-
Rsatisfiescontiguous_rangeandsized_range, - either
Rsatisfiesborrowed_rangeor 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) Constructs a span that is a view over the initializer list
il; the resulting span has size() == il.size() and data() == il.begin().
- The behavior is undefined if both extent != dynamic_extent and il.size() != extent are true.
- This overload participates in overload resolution only if std::is_const_v<element_type> is true.
9) 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
Uto element_type is at most a qualification conversion.
10) 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.
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_span_initializer_list |
202311L |
(C++26) | Constructing std::span from a std::initializer_list, (8)
|
Example
Run this code
#include <array> #include <iostream> #include <span> #include <vector> void print_span(std::span<const int> s) { for (int n : s) std::cout << n << ' '; std::cout << '\n'; } int main() { int c[]{1, 2, 3}; print_span(c); // constructs from array std::array a{4, 5, 6}; print_span(a); // constructs from std::array std::vector v{7, 8, 9}; print_span(v); // constructs from std::vector #if __cpp_lib_span_initializer_list print_span({0, 1, 2}); // constructs from initializer_list #else print_span({{0, 1, 2}}); // ditto, a workaround #endif }
Output:
1 2 3 4 5 6 7 8 9 0 1 2
See also
| direct access to the underlying contiguous storage (public member function) | |
| returns the number of elements (public member function) | |
assigns a span (public member function) | |
| (C++17)(C++20) |
returns the size of a container or array (function template) |
| (C++17) |
obtains the pointer to the underlying array (function template) |