Re: null pointer constant, address constant

From	Shao Miller <sha0.miller@gmail.com>
Newsgroups	comp.std.c
Subject	Re: null pointer constant, address constant
Date	2012-12-20 12:17 -0500
Organization	A noiseless patient Spider
Message-ID	<kavh6f$m8a$1@dont-email.me> (permalink)
References	(1 earlier) <kaq01g$6jp$1@dont-email.me> <kaqibr$gj3$1@speranza.aioe.org> <kaqmd8$u9m$1@dont-email.me> <lnzk1ark9h.fsf@nuthaus.mib.org> <89afe21d-1a8b-4749-8ad1-ec98cc65a818@a8g2000vby.googlegroups.com>

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On 12/20/2012 08:34, christian.bau wrote:
>
> Converting _any_ integer to _any_ pointer gives an implementation-
> defined result. "implementation defined" means it is defined. So the
> implementation must define what you get if you write "int x = 0; char*
> p = (char *) x; char* q = (char *) ++x; char* r = (char *) ++x;".
> There is also the requirement for the special case that an integer is,
> by chance, a null pointer constant, where the result must be a null
> pointer. So whatever definition the implementation gives, it must give
> a definition that converts 0 to a null pointer if the zero was a null
> pointer constant, therefore the definition must convert all zeroes to
> null pointers.
>

There's a jump here that I don't follow, just at the "therefore".  "So 
whatever V2 the IM gives, it must give V2 == NULL for V1 == NPC, 
therefore the IM must give V2 == NULL for V1 != NPC, also."

Since the implementation can _always_ distinguish between an NPC and a 
non-NPC, can't it satisfy the requirement without having non-NPC 0 
convert to a null pointer?  It'd seem rather useful to distinguish 
between the two, actually...

A debugger for x86 with BIOS could compare as unequal its own internal 
null pointers with a user-input-derived pointer to the Interrupt Vector 
Table.  (For example, and not that anyone does this.)

- Shao Miller

Thread

null pointer constant, address constant Szabolcs Nagy <nsz@port70.net> - 2012-12-18 13:25 +0000
  Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-18 09:53 -0500
    Re: null pointer constant, address constant Szabolcs Nagy <nsz@port70.net> - 2012-12-18 20:06 +0000
      Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-18 15:39 -0500
        Re: null pointer constant, address constant Szabolcs Nagy <nsz@port70.net> - 2012-12-19 00:44 +0000
          Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-18 20:24 -0500
            Re: null pointer constant, address constant Szabolcs Nagy <nsz@port70.net> - 2012-12-19 10:27 +0000
              Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-19 07:15 -0500
              Re: null pointer constant, address constant Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-21 03:03 +0200
                Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-21 12:13 -0500
                Re: null pointer constant, address constant Szabolcs Nagy <nsz@port70.net> - 2013-01-09 00:44 +0000
                Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2013-01-08 20:21 -0500
                Re: null pointer constant, address constant Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-01-08 20:46 -0500
          Re: null pointer constant, address constant Shao Miller <sha0.miller@gmail.com> - 2012-12-18 20:37 -0500
      Re: null pointer constant, address constant Shao Miller <sha0.miller@gmail.com> - 2012-12-18 16:15 -0500
        Re: null pointer constant, address constant Keith Thompson <kst-u@mib.org> - 2012-12-18 15:52 -0800
          Re: null pointer constant, address constant Shao Miller <sha0.miller@gmail.com> - 2012-12-18 19:12 -0500
            Re: null pointer constant, address constant Shao Miller <sha0.miller@gmail.com> - 2012-12-18 19:51 -0500
          Re: null pointer constant, address constant Keith Thompson <kst-u@mib.org> - 2012-12-18 17:02 -0800
          Re: null pointer constant, address constant "christian.bau" <christian.bau@cbau.wanadoo.co.uk> - 2012-12-20 05:34 -0800
            Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-20 10:33 -0500
              Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-20 12:28 -0500
                Re: null pointer constant, address constant Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-20 21:13 -0800
              Re: null pointer constant, address constant Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-20 21:05 -0800
            Re: null pointer constant, address constant Shao Miller <sha0.miller@gmail.com> - 2012-12-20 12:17 -0500
            Re: null pointer constant, address constant Keith Thompson <kst-u@mib.org> - 2012-12-20 12:10 -0800
              Re: null pointer constant, address constant Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-20 21:25 -0800
  Re: null pointer constant, address constant Shao Miller <sha0.miller@gmail.com> - 2012-12-18 14:02 -0500
    Re: null pointer constant, address constant Szabolcs Nagy <nsz@port70.net> - 2012-12-18 20:09 +0000
      Re: null pointer constant, address constant James Kuyper <jameskuyper@verizon.net> - 2012-12-18 15:54 -0500
        Re: null pointer constant, address constant Shao Miller <sha0.miller@gmail.com> - 2012-12-18 16:18 -0500

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