Subject: Re: lib/34632
To: None <,,>
From: Alan Barrett <>
List: netbsd-bugs
Date: 09/27/2006 20:05:04
The following reply was made to PR lib/34632; it has been noted by GNATS.

From: Alan Barrett <>
Subject: Re: lib/34632
Date: Wed, 27 Sep 2006 22:00:33 +0200

 Other people have explained that the behaviour is undefined,
 but I'll back it up with quotes from the C99 standard (ISO 9899:1999).
 On Wed, 27 Sep 2006, Antony Dovgal wrote:
 >  I mean, *I* can live with that because I don't use it, but "undefined
 >  value" in my pov doesn't include "segfault", I expect to get an
 >  undefined integer value, that's it.
 It's not an "undefined value", it's "undefined behaviour".
 See section ISO 9899:1999 section 7.4:
     The header <ctype.h> declares several functions useful for
     classifying and mapping characters.  In all cases the argument is an
     int, the value of which shall be representable as an unsigned char
     or shall equal the value of the macro EOF. If the argument has any
     other value, the behavior is undefined.
 "The value of which shall be representable [...]" means:  It's the
 application programmer's responsibility to ensure that the value
 is representable [...]".  "[The] behavior is undefined" means "If the
 application programmer fails in their responsibility, then the
 implementation may do or not do anything at all".
 The definition of "undefined behavior" in section 3.4.3 says:
     undefined behavior: behavior, upon use of a nonportable or erroneous
     program construct or of erroneous data, for which this International
     Standard imposes no requirements.
     NOTE: Possible undefined behavior ranges from ignoring the
     situation completely with unpredictable results, to behaving
     during translation or program execution in a documented manner
     characteristic of the environment (with or without the issuance of a
     diagnostic message), to terminating a translation or execution (with
     the issuance of a diagnostic message).
     EXAMPLE: An example of undefined behavior is the behavior on
     integer overflow.
 Well, you got the "unpredictable results", and it's easy to argue that
 a core dump is "termination ... with the issuance of a diagnostic
 --apb (Alan Barrett)