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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)

	  constexpr std::span<element_type,  E	/*  see	 below	*/>  subspan()
       const;
	  constexpr std::span<element_type, std::dynamic_extent>

	  subspan(			size_type		       Offset,
       (2)

	  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 ele-
       ments 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  Ex-
       tent - 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  -  Off-
       set;
	    * Otherwise, std::dynamic_extent.

Return value
	  The  requested  subspan r, such that r.data()	== this->data()	+ Off-
       set. 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
       sequence
		(public	member function)
	  last	obtains	a subspan consisting of	the last N elements of the se-
       quence
		(public	member function)

http://cppreference.com		  2022.07.31		 std::span::subspan(3)

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