Groups > comp.lang.c > #71998

Re: the language (and the role of Undefined Behavior therein)

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: the language (and the role of Undefined Behavior therein)
Date	2015-10-05 20:13 +0100
Organization	A noiseless patient Spider
Message-ID	<87r3l9jfh5.fsf@bsb.me.uk> (permalink)
References	(8 earlier) <kfn1tda6vbp.fsf@x-alumni2.alumni.caltech.edu> <d0caa5eb-5189-46a7-b6d0-84e82f59b199@googlegroups.com> <musvis$1j0$1@speranza.aioe.org> <877fn1lc3f.fsf@bsb.me.uk> <lny4fh41pf.fsf@kst-u.example.com>

Show all headers | View raw

Keith Thompson <kst-u@mib.org> writes:

> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> [...]
>> I don't think that's not really addressing supercat's point.  The
>> effective type rule renders some accesses undefined, and that is used by
>> some implementations to do what is, to some, surprising things -- like
>> not doing the access at all.  K&R 1st ed. had a notable phrase about
>> pointer conversions which was something like "the result is not
>> specified but should be unsurprising to anyone familiar with the
>> underlying address structure".  I think he or she would like to go back
>> to the days when the result of doing undefined things were largely
>> unsurprising to people in the know.
> [...]
>
> It's actually about pointer-to-integer conversions.  It's in K&R1
> Appendix A 14.4, page 210.
>
>     A pointer may be converted to any of the integral types large enough
>     to hold it.  Whether an int or a long is required is machine
>     dependent.  The mapping function is also machine dependent, but is
>     intended to be unsurprising to those who know the addressing
>     structure of the machine.  Details for some particular machines are
>     given below.

Thanks.  It seems it was a slightly less general remark than I recall,
but, given that sentiment, it's unlikely that K&R would have intended
any other pointer conversions to use a surprising mapping.

> Later in the same section, it gives details for the PDP-11, Honeywell
> 6000, IBM 370, and Interdata 8/32.  (The address structure of the
> Honeywell 6000 is peculiar by modern standards.)

I remember the Honeywell well.  I used B on one over a very slow
connection to the University of Aberdeen but that one did not run Unix
in those days.

-- 
Ben.

Thread

Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-09-29 15:48 -0700
  Re: the language (and the role of Undefined Behavior therein) Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-04 16:57 -0700
    Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-04 19:48 -0700
      Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-05 04:50 +0000
        Re: the language (and the role of Undefined Behavior therein) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-05 13:43 +0100
          Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-05 15:26 +0000
            Re: the language (and the role of Undefined Behavior therein) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-05 19:39 +0100
              Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-05 13:32 -0700
              Re: the language (and the role of Undefined Behavior therein) glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-05 22:06 +0000
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-05 16:08 -0700
                Re: the language (and the role of Undefined Behavior therein) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-06 11:04 +0100
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-06 08:06 -0700
                Re: the language (and the role of Undefined Behavior therein) Rosario19 <Ros@invalid.invalid> - 2015-10-06 18:14 +0200
                Re: the language (and the role of Undefined Behavior therein) Rosario19 <Ros@invalid.invalid> - 2015-10-06 18:54 +0200
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-06 11:20 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-06 10:00 -0700
                Re: the language (and the role of Undefined Behavior therein) David Thompson <dave.thompson2@verizon.net> - 2015-10-31 06:44 -0400
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-31 11:08 -0700
                Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-10-31 13:53 -0700
                Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-31 14:06 -0700
          Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-05 09:28 -0700
          Re: the language (and the role of Undefined Behavior therein) Keith Thompson <kst-u@mib.org> - 2015-10-05 11:20 -0700
            Re: the language (and the role of Undefined Behavior therein) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-05 20:13 +0100
              Re: the language (and the role of Undefined Behavior therein) Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-12 09:29 -0700
      Re: the language (and the role of Undefined Behavior therein) Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-12 10:32 -0700
        Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-12 12:23 -0700
        Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-12 14:42 -0700
        Re: the language (and the role of Undefined Behavior therein) supercat@casperkitty.com - 2015-10-14 09:10 -0700
          Re: the language (and the role of Undefined Behavior therein) Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-19 16:11 -0700

csiph-web