std::span::span(3)

NAME
std::span::span - std::span::span

Synopsis
   constexpr span() noexcept; (1)
   template< class It >
   explicit(extent != std::dynamic_extent) (2)
   constexpr span( It first, size_type count );
   template< class It, class End >
   explicit(extent != std::dynamic_extent) (3)
   constexpr span( It first, End last );
   template< std::size_t N > (4)
   constexpr span( element_type (&arr)[N] ) noexcept;
   template< class U, std::size_t N > (5)
   constexpr span( std::array<U, N>& arr ) noexcept;
   template< class U, std::size_t N > (6)
   constexpr span( const std::array<U, N>& arr ) noexcept;
   template< class R >
   explicit(extent != std::dynamic_extent) (7)
   constexpr span( R&& range );
   template< class U, std::size_t N >
   explicit(extent != std::dynamic_extent && N == std::dynamic_extent) (8)
   constexpr span( const std::span<U, N>& source ) noexcept;
   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)
   size
   ssize returns the size of a container or array
   (C++17) (function template)
   (C++20)
   data obtains the pointer to the underlying array
   (C++17) (function template)