Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c, comp.std.c |
| Subject | Re: when is casting (unsigned char*) to (signed char*) dangerous? |
| Date | 2012-01-23 00:37 -0800 |
| Organization | None to speak of |
| Message-ID | <lnehuqx1a7.fsf@nuthaus.mib.org> (permalink) |
| References | <j9ugaj$q30$4@speranza.aioe.org> <jfgdji$ilt$1@dont-email.me> |
Cross-posted to 2 groups.
Shao Miller <sha0.miller@gmail.com> writes:
> On 11/15/2011 14:59, tim wrote:
>> thanks in advance for your help, tim
>
> This one bothers me. We have:
> http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1310.htm
That says:
It is clear from the standard (specifically 6.2.6.2p1) that
unsigned integer types in general are not allowed to have trap
representations, and that unsigned char is not allowed to have
any padding bits.
I don't believe that conclusion is correct. 6.2.6.2p1, both in C99 and
in C11 (N1570) defines a value of an unsigned type in terms of the value
bits, but unsigned types can also have padding bits, and as the footnote
says, "some combinations of padding bits might generate trap
representations". An arithmetic operation on an unsigned type cannot
generate a trap representation, but operations that act directly on the
representation can.
[...]
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Will write code for food.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
when is typecasting (unsigned char*) to (char*) dangerous? tim <nospam@nospam.com> - 2011-11-15 19:59 +0000
Re: when is typecasting (unsigned char*) to (char*) dangerous? Kaz Kylheku <kaz@kylheku.com> - 2011-11-15 20:51 +0000
Re: when is typecasting (unsigned char*) to (char*) dangerous? tim <nospam@nospam.com> - 2011-11-16 16:55 +0000
Re: when is typecasting (unsigned char*) to (char*) dangerous? Kaz Kylheku <kaz@kylheku.com> - 2011-11-16 17:54 +0000
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-16 11:27 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Kaz Kylheku <kaz@kylheku.com> - 2011-11-16 19:49 +0000
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-16 11:52 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Kaz Kylheku <kaz@kylheku.com> - 2011-11-16 20:06 +0000
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-16 14:55 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 04:42 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? James Kuyper <jameskuyper@verizon.net> - 2011-11-16 15:15 -0500
Re: when is typecasting (unsigned char*) to (char*) dangerous? James Kuyper <jameskuyper@verizon.net> - 2011-11-16 15:24 -0500
Re: when is typecasting (unsigned char*) to (char*) dangerous? Harald van Dijk <truedfx@gmail.com> - 2011-11-16 12:41 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? James Kuyper <jameskuyper@verizon.net> - 2011-11-16 16:02 -0500
Re: when is typecasting (unsigned char*) to (char*) dangerous? Harald van Dijk <truedfx@gmail.com> - 2011-11-16 13:23 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-16 15:32 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Harald van Dijk <truedfx@gmail.com> - 2011-11-16 17:02 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? pete <pfiland@mindspring.com> - 2011-11-16 21:38 -0500
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-16 19:22 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Harald van Dijk <truedfx@gmail.com> - 2011-11-16 23:08 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-16 23:46 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Harald van Dijk <truedfx@gmail.com> - 2011-11-17 09:15 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-25 04:54 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Vincenzo Mercuri <vincenzo.mercuri@yahoo.it> - 2011-11-16 21:44 +0100
Re: when is typecasting (unsigned char*) to (char*) dangerous? Kenneth Brody <kenbrody@spamcop.net> - 2011-11-16 13:17 -0500
Re: when is typecasting (unsigned char*) to (char*) dangerous? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-11-16 00:58 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-11-16 01:36 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Markus Wichmann <nullplan@gmx.net> - 2011-11-16 13:28 +0100
Re: when is typecasting (unsigned char*) to (char*) dangerous? nroberts <roberts.noah@gmail.com> - 2011-11-16 08:14 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? BGB <cr88192@hotmail.com> - 2011-11-16 12:03 -0700
Re: when is typecasting (unsigned char*) to (char*) dangerous? blp@cs.stanford.edu (Ben Pfaff) - 2011-11-16 08:58 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Vincenzo Mercuri <vincenzo.mercuri@yahoo.it> - 2011-11-16 19:04 +0100
Re: when is typecasting (unsigned char*) to (char*) dangerous? Ben Pfaff <blp@cs.stanford.edu> - 2011-11-16 10:05 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-16 11:19 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Vincenzo Mercuri <vincenzo.mercuri@yahoo.it> - 2011-11-16 20:58 +0100
Re: when is typecasting (unsigned char*) to (char*) dangerous? Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-11-18 15:37 +0200
Re: when is typecasting (unsigned char*) to (char*) dangerous? Vincenzo Mercuri <vincenzo.mercuri@yahoo.it> - 2011-11-18 19:41 +0100
Re: when is typecasting (unsigned char*) to (char*) dangerous? Vincenzo Mercuri <vincenzo.mercuri@yahoo.it> - 2011-11-18 19:43 +0100
Re: when is typecasting (unsigned char*) to (char*) dangerous? Lauri Alanko <la@iki.fi> - 2011-11-17 19:09 +0000
Re: when is typecasting (unsigned char*) to (char*) dangerous? Harald van Dijk <truedfx@gmail.com> - 2011-11-17 11:44 -0800
Re: when is typecasting (unsigned char*) to (char*) dangerous? Keith Thompson <kst-u@mib.org> - 2011-11-17 13:16 -0800
Re: when is casting (unsigned char*) to (signed char*) dangerous? Shao Miller <sha0.miller@gmail.com> - 2012-01-22 02:22 -0500
Re: when is casting (unsigned char*) to (signed char*) dangerous? Harald van Dijk <haraldvdijk@gmail.com> - 2012-01-22 12:14 -0800
Re: when is casting (unsigned char*) to (signed char*) dangerous? Keith Thompson <kst-u@mib.org> - 2012-01-23 00:37 -0800
Re: when is casting (unsigned char*) to (signed char*) dangerous? Jens Gustedt <jens.gustedt@loria.fr> - 2012-01-24 15:10 +0100
Re: when is casting (unsigned char*) to (signed char*) dangerous? Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-26 08:55 -0800
Re: when is casting (unsigned char*) to (signed char*) dangerous? Keith Thompson <kst-u@mib.org> - 2012-01-26 11:32 -0800
Re: when is casting (unsigned char*) to (signed char*) dangerous? Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-31 21:57 -0800
Re: when is casting (unsigned char*) to (signed char*) dangerous? Shao Miller <sha0.miller@gmail.com> - 2012-02-01 01:12 -0500
Re: when is casting (unsigned char*) to (signed char*) dangerous? Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-26 08:48 -0800
csiph-web