Re: Null pointer constant

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From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: Null pointer constant
Date	Wed, 21 Jun 2017 09:54:43 -0700
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Tim Rentsch <txr@alumni.caltech.edu> writes:
[...]
> In comp.lang.c there is a game some people like to play, which
> might be called "let's pretend the meaning of English words
> and phrases used in the Standard is single-valued (and by the
> way uses the values that I think it should)".  Usually it's
> easy to tell when people are playing it, because there are
> giveaway phrases like "literal meaning" or "strictly speaking"
> or "what the words actually say" in the comments.  It's a fun
> game, and I play it myself on occasion.  However, please don't
> fall into the trap of making it more than it is, because even
> though it's fun to play it doesn't match how the authors of
> the Standard interpret the text.

To some extent, sure, it can be a game, but that's not all it is.
For example, when I point out that the definition of "expression"
is flawed, I'm not arguing that 0 really isn't an expression.
Rather, I'm advocating a change to the wording of the standard to
reflect its intent -- and meanwhile, I accept the need to use a bit
of common sense, using the obvious intent behind the words rather
than the literal words themselves to determine what is and is not
an expression.

> In an expression-statement like '0;', there is no doubt that '0'
> is an expression and also an operand within that expression.

Could it be that you're playing the game yourself?

We have two inconsistent definitions, a definition of "expression"
that requires it to include "operands", and a definition of
"operand", "an entity on which an operator acts".  The latter seems
clear, unambiguous, and consistent with the usual English meaning of
the word -- which suggests that it's the definition of "expression"
that needs to be fixed.

I have no doubt that 0 is an expression.  I do not believe that, if it
appears as a full expression, it is an "operand", nor do I think it's
useful to invent a mythical implicit "operator" to make it one.

On the other hand, the term "operand" could be redefined, but I
don't think that's the simplest and clearest solution.

I'd like a definition of "expression" that does not require it to
contain operators and/or operands.  Simply deferring to the grammar
is one way to do that.

[...]

> For 6.6 p6, it might seem like "operand" is being used in a way
> that is not consistent with its definition.

The definition of "constant expression" also needs some work, I think.
On the other hand, I've read that definition before and not noticed
the problems; I subconsciously glossed over the inconsistencies.

>                                              What is actually
> going on is more subtle.  In most cases where the Standard uses
> "operand" there is an abuse of language going on.  Consider an
> expression like '1+2*3'.  The operator '+' does not "act on" the
> expression '2*3'.  Rather the operation of addition "acts on" the
> result of evaluating '2*3'.  There is an inherent ambiguity
> between results at runtime and their corresponding syntactic
> forms at translation time.

Yes, glossing over the distinction between constructs that appear
in C source and/or at compile time vs. constructs that exist at run
time is very common, and may be nearly inevitable.  Describing the
language in a way that always makes that distinction clearly might
be an interesting challange.  Doing so in a way that's legible to
a typical reader would be even more so.

[snip]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

Null pointer constant bartc <bc@freeuk.com> - 2017-06-18 17:15 +0100
  Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-18 11:20 -0700
  Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-18 19:23 +0100
    Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-18 20:57 +0100
      Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-18 13:38 -0700
        Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-19 04:35 -0700
          Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-19 18:08 +0000
            Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-19 21:05 -0700
          Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 12:12 -0700
            Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-19 21:08 -0700
      Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-19 00:34 +0100
        Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-19 04:45 -0700
          Re: Null pointer constant David Brown <david.brown@hesbynett.no> - 2017-06-19 13:55 +0200
        Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 13:16 +0100
          Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-19 16:58 +0100
  Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-18 20:58 +0000
    Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 00:11 +0100
      Re: Null pointer constant David Brown <david.brown@hesbynett.no> - 2017-06-19 03:21 +0200
        Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 10:11 +0100
          Re: Null pointer constant David Brown <david.brown@hesbynett.no> - 2017-06-19 12:38 +0200
            Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 13:05 +0100
              Re: Null pointer constant David Brown <david.brown@hesbynett.no> - 2017-06-19 14:39 +0200
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-19 11:06 -0400
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-19 15:51 +0000
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-19 12:22 -0400
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-19 17:29 +0000
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-19 13:45 -0400
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 12:31 -0700
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-19 15:10 +0000
                Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-19 16:53 +0100
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-19 13:06 -0400
                Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-19 20:03 +0100
                Re: Null pointer constant David Brown <david.brown@hesbynett.no> - 2017-06-19 22:37 +0200
                Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-19 22:10 +0100
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 14:25 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-19 22:46 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-20 08:43 -0700
                Re: Null pointer constant supercat@casperkitty.com - 2017-06-20 09:17 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-21 00:56 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-21 10:07 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-21 23:52 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-22 10:12 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-22 17:33 -0700
                Re: Null pointer constant supercat@casperkitty.com - 2017-06-23 08:54 -0700
                Re: Null pointer constant Manfred <invalid@invalid.add> - 2017-06-20 00:00 +0200
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 15:27 -0700
                Re: Null pointer constant supercat@casperkitty.com - 2017-06-19 16:38 -0700
                Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-20 01:14 +0100
                Re: Null pointer constant Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-20 12:03 +0100
                Re: Null pointer constant Manfred <noname@invalid.add> - 2017-06-20 13:16 +0200
                Re: Null pointer constant jameskuyper@verizon.net - 2017-06-20 05:34 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-20 08:49 -0700
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-20 16:35 +0000
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-20 13:07 -0400
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-20 17:29 +0000
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-20 13:55 -0400
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-20 18:06 +0000
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-20 14:42 -0400
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-20 19:10 +0000
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-20 18:31 +0000
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-20 18:36 +0000
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-20 14:45 -0400
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-20 17:14 +0000
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-20 11:55 -0700
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-20 19:23 +0000
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-20 15:39 -0400
                Re: Null pointer constant scott@slp53.sl.home (Scott Lurndal) - 2017-06-21 13:44 +0000
                Re: Null pointer constant scott@slp53.sl.home (Scott Lurndal) - 2017-06-21 13:49 +0000
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-21 23:57 -0700
                Re: Null pointer constant Philip Lantz <prl@canterey.us> - 2017-06-28 20:04 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-07-10 08:38 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-20 12:39 -0700
                Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-20 20:53 +0100
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-20 13:07 -0700
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-20 20:50 +0000
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-20 15:35 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-21 00:26 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-21 09:54 -0700
                Re: Null pointer constant "James R. Kuyper" <jameskuyper@verizon.net> - 2017-06-21 13:09 -0400
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-22 00:53 -0700
                Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-21 18:09 +0100
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-22 00:50 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 10:24 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-19 22:32 -0700
                Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 19:40 +0100
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 12:08 -0700
                Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 20:32 +0100
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 12:48 -0700
                Re: Null pointer constant jameskuyper@verizon.net - 2017-06-19 13:08 -0700
                Re: Null pointer constant Nick Bowler <nbowler@draconx.ca> - 2017-06-19 20:40 +0000
                Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 22:01 +0100
                Re: Null pointer constant supercat@casperkitty.com - 2017-06-19 14:15 -0700
                Re: Null pointer constant jameskuyper@verizon.net - 2017-06-19 14:25 -0700
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-19 21:06 +0000
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 14:28 -0700
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-19 21:35 +0000
                Re: Null pointer constant supercat@casperkitty.com - 2017-06-19 14:48 -0700
                Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-20 15:38 +0000
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 15:16 -0700
                Re: Null pointer constant supercat@casperkitty.com - 2017-06-19 14:29 -0700
                Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 15:18 -0700
                Re: Null pointer constant Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-19 22:48 -0700
                Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-20 15:09 +0100
              Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 10:19 -0700
            Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 10:15 -0700
              Re: Null pointer constant David Brown <david.brown@hesbynett.no> - 2017-06-19 22:44 +0200
            Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 12:24 -0700
      Re: Null pointer constant Ike Naar <ike@iceland.freeshell.org> - 2017-06-19 08:21 +0000
        Re: Null pointer constant bartc <bc@freeuk.com> - 2017-06-19 10:17 +0100
          Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 10:04 -0700
  Re: Null pointer constant Keith Thompson <kst-u@mib.org> - 2017-06-19 12:34 -0700

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