Re: C scope and struct definitions

Message-ID	<4FE9A080.4020608@loria.fr> (permalink)
Date	2012-06-26 13:44 +0200
From	Jens Gustedt <jens.gustedt@loria.fr>
Newsgroups	comp.lang.c
Subject	Re: C scope and struct definitions
References	(6 earlier) <js5omi$obb$1@dont-email.me> <js5t15$bln$1@dont-email.me> <js5vcd$l8p$1@dont-email.me> <jsa79j$ern$1@dont-email.me> <4FE8B219.4080409@verizon.net>
Organization	Guest of ProXad - France

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Am 25.06.2012 20:46, schrieb James Kuyper:
> On 06/25/2012 01:31 PM, Nick Bowler wrote:
>> ... However, it's easy to construct a program
>> (i.e., "existing working code") that would break if you made this
>> change.  The following is valid in C today:
>>
>>   int main(void) {
>>     void foo(struct baz { int x; } *);
>>     void bar(struct baz { int x; } *);
>>
>>     foo(0);
>>     bar(0);
> 
> Note that this code depends upon the fact that a null pointer constant
> gets implicitly converted to the parameter's type - no explicit
> conversion is needed. This is good, because C doesn't provide any way to
> explicitly specify a target type compatible with the the parameter's type.
> 
> In essence, such a declaration says "don't use this function with any
> arguments except null pointer constants". It would be simpler to have
> the function take no argument at all.

no, you forget another important possible use case, void*. E.g
something like

foo(malloc(bigNumber));

would be a valid call as well.

>> (Note that for the above function calls work, foo and bar *must* be
>> defined in a separate translation unit for the struct compatibility
>> rules in C11§6.2.7p1 to apply).

yes, thing that I always found bizarre

Another resolution of this scope problem would be to do the same as
C11 allows for typedef's: if the type is exactly the same (this could
reuse the wording of the section for compatible type) then a
redefinition could be allowed.

>> That being said, breaking the above program may be a good thing.
> 
> I think so.

definitively

Jens

Thread

C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-22 13:30 -0400
  Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-22 14:02 -0400
    Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-22 22:40 +0000
      Re: C scope and struct definitions Ben Pfaff <blp@cs.stanford.edu> - 2012-06-22 15:47 -0700
      Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-22 20:32 -0400
        Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-23 22:06 +0000
          Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 16:18 -0700
            Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-25 10:19 -0400
              Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-25 11:51 -0700
          Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 19:54 -0400
            Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 00:56 +0000
              Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 21:48 -0400
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 06:03 +0000
                Re: C scope and struct definitions nick_keighley_nospam@hotmail.com - 2012-06-25 00:05 -0700
              Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 19:25 -0700
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-24 05:40 +0000
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-24 10:47 +0200
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-24 11:00 -0700
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-25 03:53 +0000
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-25 01:14 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-24 22:38 -0700
                Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:03 -0400
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 20:08 +0000
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 23:21 +0200
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 21:47 +0000
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 18:05 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-26 16:45 -0700
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-27 08:26 +0200
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 00:01 -0700
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-27 06:57 -0400
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-27 15:00 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 14:48 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 16:14 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-29 09:36 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 16:27 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:03 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:11 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-27 15:53 -0700
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 17:59 -0400
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-26 22:18 +0000
                Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-26 18:33 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-26 17:22 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 00:03 -0700
                Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-27 14:13 -0400
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-27 12:15 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-29 09:43 -0700
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-29 11:59 -0700
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-07-01 18:32 -0700
                Re: C scope and struct definitions pacman@kosh.dhis.org (Alan Curry) - 2012-06-27 20:59 +0000
                Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-28 16:42 -0400
            Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-23 20:57 -0400
              Re: C scope and struct definitions Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-06-23 22:11 -0400
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-23 22:51 -0400
                Re: C scope and struct definitions Nick Bowler <nbowler@draconx.ca> - 2012-06-25 17:31 +0000
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-25 14:46 -0400
                Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-25 14:43 -0700
                Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-26 13:44 +0200
                Re: C scope and struct definitions Keith Thompson <kst-u@mib.org> - 2012-06-23 20:07 -0700
              Re: C scope and struct definitions Jens Gustedt <jens.gustedt@loria.fr> - 2012-06-24 10:56 +0200
                Re: C scope and struct definitions James Kuyper <jameskuyper@verizon.net> - 2012-06-24 08:29 -0400
              Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-24 10:26 -0700
          Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 10:50 -0400
      Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-24 09:23 -0700
        Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:17 -0400
          Re: C scope and struct definitions Tim Rentsch <txr@alumni.caltech.edu> - 2012-06-25 14:22 -0700
  Re: C scope and struct definitions Kenneth Brody <kenbrody@spamcop.net> - 2012-06-25 11:11 -0400

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