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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c++
Subject: Re: Is this really necessary
Date: Sat, 07 Aug 2021 12:59:02 -0700
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Xref: csiph.com comp.lang.c++:80791

Richard Damon <Richard@Damon-Family.org> writes:

> On 6/5/21 9:06 AM, Bonita Montero wrote:
>
>>> No.  Subtraction of pointers is defined as the difference in their
>>> indexes within a single array.
>>
>> That coudn't be true because you can cast any pointer-pair
>> to char *, subtract them and use the difference for memcpy().
>
> Actually it is true.  Char (and its relatives) do have a few special
> cases, as Any pointer is allowed to be converted into a pointer to char
> and back and still be used.  Also I believe that any object can be
> treated as an array of char.  So you can do the conversion to char and
> subtract for two pointers in the same object.

In C the difference of two pointers might not work, in particular
if the result doesn't fit in ptrdiff_t.  I don't know if that
rule is different in C++.