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Re: Do not cast pointers to functions to pointers to primitive types

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On 09/04/2012 04:27 PM, Alan Curry wrote:
> In article <lntxvettoe.fsf@nuthaus.mib.org>,
> Keith Thompson  <kst-u@mib.org> wrote:
>>
>> So you don't want to distinguish between casts whose behavior
>> is well defined, those whose behavior is implementation-defined,
>> and those whose behavior is completely undefined?
>>
>> I can understand that opinion, but it hardly seems reasonable to
>> call those who disagrees with it idiots.
>>
>> Casts are commonly interpreted to mean "Shut up, compiler, I know
>> what I'm doing"-- but the standard doesn't say or imply that.
>>
>> How do you feel about casts applied to struct types, which are a
>> constraint violation?
> 
> Those are errors, not warnings. You can't cast away an error.
> 
> Failure to distinguish errors and warnings is a problem that only The
> Standard has. In the real world everybody knows they're different.

The standard cannot distinguish between error messages and warning
messages, because whether or not something constitutes an error is
highly dependent on factors outside the scope of the standard. The code
in question has undefined behavior, the worst thing that the standard
can say about any code construct. However, the X/Open standard does
define the behavior (a fact which is outside the scope of the C
standard). A programmer who decides to write code which relies upon that
definition, believing that it will only ever need to be run on systems
that conform to the X/Open standard (something else that is also outside
the scope of the C standard) is NOT making an error (unless that belief
is incorrect).

The standard leaves the distinction between errors and warnings up to
the implementations. Were you rewriting the C standard to remove that
freedom, how would you make that distinction in such a way as to apply
to cases like this? It seems to me that a mind-reading compiler with the
capacity to make better judgements than the developer about the
reasonability of such beliefs is needed, in order to make that distinction.

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Thread

Do not cast pointers to functions to pointers to primitive types ajaybgr <ajay.bgr@gmail.com> - 2012-09-03 01:50 -0700
  Re: Do not cast pointers to functions to pointers to primitive types Ian Collins <ian-news@hotmail.com> - 2012-09-03 20:59 +1200
  Re: Do not cast pointers to functions to pointers to primitive types Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-09-03 02:13 -0700
  Re: Do not cast pointers to functions to pointers to primitive types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-09-03 11:24 +0100
  Re: Do not cast pointers to functions to pointers to primitive types James Kuyper <jameskuyper@verizon.net> - 2012-09-03 08:31 -0400
    Re: Do not cast pointers to functions to pointers to primitive types Keith Thompson <kst-u@mib.org> - 2012-09-03 13:21 -0700
      Re: Do not cast pointers to functions to pointers to primitive types James Kuyper <jameskuyper@verizon.net> - 2012-09-03 16:57 -0400
        Re: Do not cast pointers to functions to pointers to primitive types Keith Thompson <kst-u@mib.org> - 2012-09-03 14:48 -0700
          Re: Do not cast pointers to functions to pointers to primitive types pacman@kosh.dhis.org (Alan Curry) - 2012-09-03 21:57 +0000
            Re: Do not cast pointers to functions to pointers to primitive types Keith Thompson <kst-u@mib.org> - 2012-09-03 18:11 -0700
              Re: Do not cast pointers to functions to pointers to primitive types pacman@kosh.dhis.org (Alan Curry) - 2012-09-04 02:03 +0000
                Re: Do not cast pointers to functions to pointers to primitive types Keith Thompson <kst-u@mib.org> - 2012-09-03 19:20 -0700
                Re: Do not cast pointers to functions to pointers to primitive types pacman@kosh.dhis.org (Alan Curry) - 2012-09-04 20:27 +0000
                Re: Do not cast pointers to functions to pointers to primitive types James Kuyper <jameskuyper@verizon.net> - 2012-09-04 17:10 -0400
                Re: Do not cast pointers to functions to pointers to primitive types Barry Schwarz <schwarzb@dqel.com> - 2012-09-04 14:14 -0700
          Re: Do not cast pointers to functions to pointers to primitive types pete <pfiland@mindspring.com> - 2012-09-03 22:51 -0400
      Re: Do not cast pointers to functions to pointers to primitive types Vincenzo Mercuri <vincenzo.mercuri@yahoo.it> - 2012-09-04 00:02 +0200
        Re: Do not cast pointers to functions to pointers to primitive types Keith Thompson <kst-u@mib.org> - 2012-09-03 18:19 -0700
  Re: Do not cast pointers to functions to pointers to primitive types Kaz Kylheku <kaz@kylheku.com> - 2012-09-04 01:18 +0000
    Re: Do not cast pointers to functions to pointers to primitive types "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2012-09-04 11:59 -0400
      Re: Do not cast pointers to functions to pointers to primitive types Philip Lantz <prl@canterey.us> - 2012-09-06 21:34 -0700

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