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std::ptrdiff_t(3)	      C++ Standard Libary	     std::ptrdiff_t(3)

NAME
       std::ptrdiff_t -	std::ptrdiff_t

Synopsis
	  Defined in header <cstddef>
	  typedef /*implementation-defined*/ ptrdiff_t;

	  std::ptrdiff_t is the	signed integer type of the result of subtract-
       ing two pointers.

	  The bit width	of std::ptrdiff_t is not less than 17. (since C++11)

Notes
	  std::ptrdiff_t is used for pointer arithmetic	and array indexing, if
       negative	values
	  are  possible.  Programs that	use other types, such as int, may fail
       on, e.g.	64-bit
	  systems when the index exceeds INT_MAX or if	it  relies  on	32-bit
       modular arithmetic.

	  When working with the	C++ container library, the proper type for the
       difference
	  between  iterators  is  the member typedef difference_type, which is
       often synonymous
	  with std::ptrdiff_t.

	  Only pointers	to elements of the same	array (including  the  pointer
       one past	the end
	  of the array)	may be subtracted from each other.

	  If an	array is so large (greater than	PTRDIFF_MAX elements, but less
       than SIZE_MAX
	  bytes),  that	 the difference	between	two pointers may not be	repre-
       sentable	as
	  std::ptrdiff_t, the result of	subtracting two	such pointers is unde-
       fined.

	  For char arrays shorter than PTRDIFF_MAX, std::ptrdiff_t acts	as the
       signed
	  counterpart of std::size_t: it can store the size of	the  array  of
       any type	and is,
	  on most platforms, synonymous	with std::intptr_t.

	  It  is  unspecified  whether	the  declaration  of std::ptrdiff_t is
       available in any
	  other	standard library header. An implementation may avoid introduc-
       ing this	name
	  even when the	standard requires std::ptrdiff_t to be used.

Possible implementation
	  // valid since C++11
	  using	 ptrdiff_t  =	decltype(static_cast<int*>(nullptr)   -	  sta-
       tic_cast<int*>(nullptr));

Example
       // Run this code

	#include <cstddef>
	#include <iostream>

	int main()
	{
	    const std::size_t N	= 10;
	    int* a = new int[N];
	    int* end = a + N;
	    for	(std::ptrdiff_t	i = N; i > 0; --i)
		std::cout << (*(end - i) = i) << ' ';
	    std::cout << '\n';
	    delete[] a;
	}

Output:
	10 9 8 7 6 5 4 3 2 1

See also
	  size_t   unsigned integer type returned by the sizeof	operator
		   (typedef)
		   byte	offset from the	beginning of a standard-layout type to
       specified
	  offsetof member
		   (function macro)
	  C documentation for
	  ptrdiff_t

http://cppreference.com		  2024.06.10		     std::ptrdiff_t(3)

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