std::span::subspan(3) - FreeBSD Ports 15.1.quarterly Manual Pages

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std::span::subspan(3)	       C++ Standard Libary	   std::span::subspan(3)

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

Synopsis
	template< std::size_t Offset,

		  std::size_t  Count  = std::dynamic_extent >	      (1) (since
     C++20)
	constexpr std::span<element_type, E /* see below */>

	    subspan() const;
	constexpr std::span<element_type, std::dynamic_extent>

	    subspan( size_type Offset,				     (2)  (since
     C++20)

		     size_type Count = std::dynamic_extent ) const;

	Obtains  a  span  that	is  a  view over the Count elements of this span
     starting at
	offset Offset. If Count is std::dynamic_extent, the number  of	elements
     in the
	subspan is size() - offset (i.e., it ends at the end of *this).

	1) Is ill-formed if
	  * Offset is greater than Extent, or
	  *  Count is not std::dynamic_extent and Count is greater than Extent -
     Offset.

	The behavior is undefined if either Offset or Count  is  out  of  range.
     This happens if

	  * Offset is greater than size(), or
	  *  Count is not std::dynamic_extent and Count is greater than size() -
     Offset.

	The extent E of the span returned by (1) is determined as follows:

	  * If Count is not std::dynamic_extent, Count;
	  * Otherwise, if Extent is not std::dynamic_extent, Extent - Offset;
	  * Otherwise, std::dynamic_extent.

Return value
	The requested subspan r, such that r.data() == this->data() + Offset. If
     Count is
	std::dynamic_extent,  r.size()	==  this->size()  -  Offset;   otherwise
     r.size() == Count.

Example
     // Run this code

      #include <algorithm>
      #include <cstdio>
      #include <numeric>
      #include <ranges>
      #include <span>

      void display(std::span<const char> abc)
      {
	  const auto columns{20U};
	  const auto rows{abc.size() - columns + 1};

	  for (auto offset{0U}; offset < rows; ++offset)
	  {
	      std::ranges::for_each(abc.subspan(offset, columns), std::putchar);
	      std::putchar('\n');
	  }
      }

      int main()
      {
	  char abc[26];
	  std::iota(std::begin(abc), std::end(abc), 'A');
	  display(abc);
      }

Output:
      ABCDEFGHIJKLMNOPQRST
      BCDEFGHIJKLMNOPQRSTU
      CDEFGHIJKLMNOPQRSTUV
      DEFGHIJKLMNOPQRSTUVW
      EFGHIJKLMNOPQRSTUVWX
      FGHIJKLMNOPQRSTUVWXY
      GHIJKLMNOPQRSTUVWXYZ

See also
	first  obtains	a  subspan consisting of the first N elements of the se-
     quence
	      (public member function)
	last  obtains a subspan consisting of the last N  elements  of	the  se-
     quence
	      (public member function)

http://cppreference.com 	   2024.06.10		   std::span::subspan(3)
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