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Re: on understanding & and pointer arithmetic

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David Brown <david.brown@hesbynett.no> writes:
> On 16/12/2021 20:25, Meredith Montgomery wrote:
[...]
>> Yes, so that corrects me at least once.  I didn't think &a would be of a
>> different type.  So the type of &a is array of 13 char.  I get that.
>
> /No/.  "a" is of type "array of 13 char".  "&a" is of type "pointer to
> array of 13 char".  These are different.
>
>> The value of &a is the same /value/ as &a[0].  I also get that.  I'm
>> good here.
>
> Correct.  As Ben said (and Ben is very good at explaining things
> accurately), a pointer has a type and has an address as it's value.  So
> the values of pointers here are the same, but the pointers themselves
> are different because they have different types.

I don't think I'd say that &a and &a[0] have the same *value*, though it
depends on just what you mean by "value".

They refer to the same location in memory, so that `(void*)&a` and
`(void*)&a[0]` do have the same value.  But they're of different types,
and a "value" in C includes its type.  This can get a bit vague at
times, and it's common to handwave away the difference, even in the
standard.  It can be particularly vague when were talking about numeric
values; are 3, 3U, and 3.0 the same value?

Note that `&a == &a[0]` is a constraint violation, in case you were
thinking that "same value" can be defined in terms of equality.

For pointers of different types, I suggest avoiding the issue by saying
that they refer to the same location.

The standard's definition of "value" (N1570 3.19) is:

    precise meaning of the contents of an object when interpreted as
    having a specific type

That definition is incomplete, since it excludes a "value" that results
from evaluation an expression.  `2+2` has a value (spoiler: it's 4), but
that value is not the contents of any object.

[...]

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */

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on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 11:13 -0300
  Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-16 14:23 +0000
    Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 11:57 -0300
      Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 17:42 +0000
        Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-16 18:14 +0000
          Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 21:14 +0000
        Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 16:42 -0300
          Re: on understanding & and pointer arithmetic Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 12:44 -0800
            Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:06 -0300
          Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 21:34 +0000
            Re: on understanding & and pointer arithmetic Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 14:14 -0800
              Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 23:44 +0000
            Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:09 -0300
  Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-16 16:23 +0100
    Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-16 16:25 -0300
      Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-16 21:08 +0100
        Re: on understanding & and pointer arithmetic Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-12-16 12:54 -0800
          Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-17 10:53 +0100
            Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 11:39 -0300
              Re: on understanding & and pointer arithmetic scott@slp53.sl.home (Scott Lurndal) - 2021-12-18 16:31 +0000
              Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-18 18:56 +0100
                Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-25 21:29 -0300
              Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-18 18:29 +0000
        Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 11:32 -0300
    Re: on understanding & and pointer arithmetic Manfred <noname@add.invalid> - 2021-12-16 21:34 +0100
      Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 22:20 +0000
        Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:02 -0300
          Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:34 -0300
          Re: on understanding & and pointer arithmetic Manfred <noname@add.invalid> - 2021-12-18 18:36 +0100
          Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-18 21:17 +0000
      Re: on understanding & and pointer arithmetic James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-16 18:59 -0500
  Re: on understanding & and pointer arithmetic James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-16 18:38 -0500
    Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-16 23:50 +0000
      Re: on understanding & and pointer arithmetic "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-12-17 07:34 -0800
        Re: on understanding & and pointer arithmetic Bart <bc@freeuk.com> - 2021-12-17 17:48 +0000
    Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-16 23:56 +0000
      Re: on understanding & and pointer arithmetic James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-12-16 19:06 -0500
        Re: on understanding & and pointer arithmetic Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-17 00:10 +0000
        Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:32 -0300
    Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:30 -0300
  Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-17 11:08 +0100
    Re: on understanding & and pointer arithmetic Manfred <noname@add.invalid> - 2021-12-17 16:24 +0100
      Re: on understanding & and pointer arithmetic David Brown <david.brown@hesbynett.no> - 2021-12-17 18:17 +0100
    Re: on understanding & and pointer arithmetic Meredith Montgomery <mmontgomery@levado.to> - 2021-12-18 12:11 -0300

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