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Re: C11 6.3.2.3p7 Referenced Type

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From Wojtek Lerch <wojtek_l@yahoo.ca>
Newsgroups comp.std.c
Subject Re: C11 6.3.2.3p7 Referenced Type
Date Thu, 10 Jan 2013 17:45:09 -0500
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On 07-Jan-13 1:29 AM, Shao Miller wrote:
> On 1/7/2013 00:07, Wojtek Lerch wrote:
>> In other words, does the standard guarantee that (char*)(int*)&x, if
>> defined, must be equal to (char*)&x?
>
> (I think you meant to ask about '(char*)(int*)&f' and '(char*)&f', and
> 'n' seems to have lost its relevance.)

Actually I meant to ask generally, without necessarily referring to the 
code above -- substitute "(char*)(int*)&lval" and "(char*)&lval"...  The 
only relevance of "n" was as a possible reference in "What if 
(int*)&lval points to some other object, let's call it 'n'?"

> I think that example has the same consideration as the last one.  If 'p'
> (or '(int*)&f' can point to an object than than 'f', then '(char*)p' can
> point to the lowest-addressed byte of that other object.  But
> '(float*)p' had better point to 'f' again.

Right.  But maybe it's a better example.

> One way this might happen is if, for the values of 'int *' and 'float
> *', pointers are simply indices, and '&f' means "the first float in the
> program" and '&n' means "the first int in the program".  'char *' and
> 'void *' (etc.) might have a greater range of meanings/values.

> Eep.  This would be scary.

Sure; this doesn't sound like a practical rule that a sane 
implementation might reasonably want to apply to all programs. 
Typically for C, unions and pointers to allocated memory mess things up. 
  But as far as I know, implementations aren't required to apply the 
same rules to all programs -- if a compiler only applies your 
index-based implementation of pointers only for programs that are simple 
enough to make it work, that's good enough as an example.

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Thread

C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-04 02:08 -0500
  Re: C11 6.3.2.3p7 Referenced Type Keith Thompson <kst-u@mib.org> - 2013-01-04 08:09 -0800
    Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-04 12:25 -0500
    Re: C11 6.3.2.3p7 Referenced Type lawrence.jones@siemens.com - 2013-01-04 13:47 -0500
      Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-04 14:56 -0500
        Re: C11 6.3.2.3p7 Referenced Type lawrence.jones@siemens.com - 2013-01-04 17:10 -0500
          Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-04 20:34 -0500
  Re: C11 6.3.2.3p7 Referenced Type Wojtek Lerch <wojtek_l@yahoo.ca> - 2013-01-04 23:45 -0500
    Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-05 02:07 -0500
      Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-05 02:16 -0500
    Re: C11 6.3.2.3p7 Referenced Type Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-06 17:25 -0800
      Re: C11 6.3.2.3p7 Referenced Type Wojtek Lerch <wojtek_l@yahoo.ca> - 2013-01-06 22:13 -0500
        Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-06 23:30 -0500
          Re: C11 6.3.2.3p7 Referenced Type Wojtek Lerch <wojtek_l@yahoo.ca> - 2013-01-07 00:07 -0500
            Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-07 01:29 -0500
              Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-07 02:18 -0500
              Re: C11 6.3.2.3p7 Referenced Type Wojtek Lerch <wojtek_l@yahoo.ca> - 2013-01-10 17:45 -0500
          Re: C11 6.3.2.3p7 Referenced Type Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-06 22:30 -0800
            Re: C11 6.3.2.3p7 Referenced Type Shao Miller <sha0.miller@gmail.com> - 2013-01-07 01:58 -0500
              Re: C11 6.3.2.3p7 Referenced Type Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-06 23:16 -0800
        Re: C11 6.3.2.3p7 Referenced Type Tim Rentsch <txr@alumni.caltech.edu> - 2013-01-06 22:02 -0800

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