Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #100534

Re: Octal

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.lang.c
Subject Re: Octal
Date 2016-12-28 22:05 +0100
Organization A noiseless patient Spider
Message-ID <o419c8$vfm$1@dont-email.me> (permalink)
References (15 earlier) <o406lc$b3e$1@dont-email.me> <o408am$fuc$1@dont-email.me> <ln60m455ab.fsf@kst-u.example.com> <o40ta0$j5t$1@dont-email.me> <ln7f6j4yd4.fsf@kst-u.example.com>

Show all headers | View raw

On 28/12/16 21:01, Keith Thompson wrote:
> BartC <bc@freeuk.com> writes:
>> On 28/12/2016 17:31, Keith Thompson wrote:
>>> BartC <bc@freeuk.com> writes:
>>> [...]
>>>> But if a compiler is going to think up ways that a programmer may have
>>>> written numbers wrongly then what about:
>>>>
>>>>   0x123E3
>>>>
>>>> Maybe /this/ should have been written as 0x123p3!
>>>>
>>>> Or 123E3, which was supposed to be 0x123E3 but the the "0x" was left
>>>> out. Or 0123E3, when the "x" is left out.
>>>>
>>>> Why is the compiler not giving errors in these cases? Surely they must
>>>> count as pp-numbers too.
>>>
>>> 0x123E3 is a perfectly valid hexadecimal integer constant.  123E3 is a
>>> perfectly valid floating constant.  Yes, they're valid pp-numbers, and
>>> they're converted to valid constants in translation phase 7.  That's why
>>> compilers don't print error messages for them -- because they're not
>>> errors.
>>>
>>> I've already explained why 0x123e+3 is a syntax error.  I understand
>>> that you don't like that fact; I'm not entirely pleased about it myself.
>>> But it is what it is.
>>
>> David Brown suggested the compiler messages were given because 0x123E+3
>> was ambiguous (possible user-error). In which case I gave other such
>> examples that don't generate an error.
>
> I think there may have been an ambiguous use of the word "ambiguous".
>

You are correct - the ambiguity is to human readers, not to the 
standards or to a compiler that follows them correctly here.

Compilers (the correct ones) give an error here because the standards 
say they must issue a diagnostic.  I just think it is /good/ that the 
standard says this should lead to a diagnostic rather than silently 
interpreting 0x123E+3 in some way, because it can help the developer 
spot mistakes.

> As far as the C standard is concerned, 0x123E+3 is not ambiguous.
> It is a valid pp-number that cannot be converted to a valid constant,
> resulting in a syntax error.  That's why it's diagnosed.
>
> The fact that it could be ambiguous *to a human reader* (the
> writer might have meant either `0x123E + 3` or `0x123p+3`) is an
> after-the-fact observation which suggests that treating it as a
> syntax error isn't such a bad thing.  It is *not* the underlying
> rationale for the behavior, or is it an argument that all constructs
> that might be ambiguous to a human reader should be diagnosed.
> (I don't want a compiler warning me about `2+2` because I might
> have meant `2E+2`.  Do you?)
>
> The underlying rationale has already been explained, and was
> stated by the committee in section 3.1.8 of the ANSI C rationale:
>     https://www.lysator.liu.se/c/rat/c1.html#3-1-8
>
> Just how freaking difficult is it to avoid writing 0x123E+3?
>

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Octal BartC <bc@freeuk.com> - 2016-12-27 14:08 +0000
  Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-27 06:19 -0800
    Re: Octal BartC <bc@freeuk.com> - 2016-12-27 14:58 +0000
      Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-27 07:07 -0800
        Re: Octal BartC <bc@freeuk.com> - 2016-12-27 15:22 +0000
          Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-27 07:37 -0800
            Re: Octal BartC <bc@freeuk.com> - 2016-12-27 16:24 +0000
              Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-27 08:30 -0800
              Re: Octal supercat@casperkitty.com - 2016-12-27 09:10 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 09:35 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-27 10:47 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 12:03 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-27 12:27 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 12:44 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-27 13:37 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 16:38 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-27 17:53 -0800
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-27 20:26 -0600
                Re: Octal supercat@casperkitty.com - 2016-12-27 18:48 -0800
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-27 22:20 -0600
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 18:41 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-27 19:19 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-29 14:52 +1300
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 18:41 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-28 16:54 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-27 17:44 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 12:17 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-27 22:39 +0000
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-28 11:49 +1300
                Re: Octal BartC <bc@freeuk.com> - 2016-12-27 23:09 +0000
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-28 12:32 +1300
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 00:51 +0000
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-28 14:00 +1300
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 01:13 +0000
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-27 20:04 -0600
                Re: Octal supercat@casperkitty.com - 2016-12-27 18:45 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-29 13:35 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-29 14:49 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-29 15:33 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-30 12:35 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-13 15:19 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2017-01-13 15:32 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2017-01-14 12:35 +1300
                Re: Octal Keith Thompson <kst-u@mib.org> - 2017-01-13 15:51 -0800
                Re: Octal supercat@casperkitty.com - 2017-01-13 18:25 -0800
                Re: Octal Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-14 06:21 -0800
                Re: Octal supercat@casperkitty.com - 2017-01-14 14:00 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 23:08 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 23:02 -0800
                Re: Octal supercat@casperkitty.com - 2017-01-13 18:52 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-15 23:46 -0800
                Re: Octal supercat@casperkitty.com - 2017-01-16 01:46 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-31 08:33 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 17:19 -0800
                Re: Octal raltbos@xs4all.nl (Richard Bos) - 2016-12-28 09:39 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 11:02 +0000
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-28 12:13 +0100
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 11:41 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 09:31 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 17:39 +0000
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-28 22:05 +0100
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 12:01 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 20:05 +0000
                Re: Octal asetofsymbols@gmail.com - 2016-12-28 11:20 -0800
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-28 12:01 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 12:30 +0000
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-28 13:51 +0100
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-28 16:26 +0000
                Re: Octal supercat@casperkitty.com - 2016-12-28 08:40 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 09:41 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 18:04 +0000
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-28 19:36 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 19:42 +0000
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-29 00:34 +0000
                Re: Octal supercat@casperkitty.com - 2016-12-28 11:04 -0800
                Re: Octal raltbos@xs4all.nl (Richard Bos) - 2016-12-28 12:09 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 16:46 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 00:56 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 17:52 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 11:27 +0000
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-28 12:09 +0000
                Re: Octal supercat@casperkitty.com - 2016-12-28 08:17 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 17:02 +0000
                Re: Octal Ike Naar <ike@iceland.freeshell.org> - 2016-12-28 17:25 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 17:45 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 10:21 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-28 09:27 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 10:23 -0800
                Re: Octal supercat@casperkitty.com - 2016-12-28 11:18 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 10:19 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 15:54 +0000
                Re: Octal Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-29 12:57 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-30 10:01 +1300
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-30 10:44 +0100
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-29 17:32 +0100
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 17:03 +0000
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-29 16:26 -0600
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-30 11:31 +1300
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-29 16:58 -0600
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-30 11:59 +1300
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-30 09:00 +1300
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-30 10:21 +0100
                Re: Octal asetofsymbols@gmail.com - 2016-12-30 01:29 -0800
                Re: Octal asetofsymbols@gmail.com - 2016-12-30 01:29 -0800
                Re: Octal asetofsymbols@gmail.com - 2016-12-30 01:36 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 11:52 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 17:10 +0000
                Re: Octal supercat@casperkitty.com - 2016-12-29 05:52 -0800
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-28 19:51 -0600
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 21:09 +0000
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-30 10:15 +1300
                Re: Octal Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-29 13:53 -0800
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-30 12:07 +0100
                Re: Octal BartC <bc@freeuk.com> - 2016-12-30 13:04 +0000
                Re: Octal Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-30 05:31 -0800
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-30 15:00 +0100
                Re: Octal BartC <bc@freeuk.com> - 2016-12-30 15:55 +0000
                Re: Octal David Brown <david.brown@hesbynett.no> - 2017-01-01 16:00 +0100
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2017-01-02 08:33 +1300
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2017-01-02 09:02 +1300
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2017-01-02 09:38 +1300
                Re: Octal Malcolm McLean <malcolm.mclean5@btinternet.com> - 2017-01-01 13:59 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2017-01-01 14:24 -0800
                Re: Octal supercat@casperkitty.com - 2017-01-01 15:51 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2017-01-02 13:09 +1300
                Re: Octal supercat@casperkitty.com - 2017-01-01 16:50 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2017-01-02 14:24 +1300
                Re: Octal David Brown <david.brown@hesbynett.no> - 2017-01-02 01:53 +0100
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2017-01-02 14:15 +1300
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-02 02:28 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-31 06:24 +1300
                Re: Octal BartC <bc@freeuk.com> - 2016-12-30 17:53 +0000
                Re: Octal luser droog <luser.droog@gmail.com> - 2016-12-30 10:01 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-31 09:57 +1300
                Re: Octal supercat@casperkitty.com - 2016-12-30 13:50 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-31 11:09 +1300
                Re: Octal supercat@casperkitty.com - 2016-12-30 14:46 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-31 12:28 +1300
                Re: Octal supercat@casperkitty.com - 2016-12-30 16:01 -0800
                Re: Octal Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-30 14:48 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-30 22:51 +0000
                Re: Octal supercat@casperkitty.com - 2016-12-30 15:20 -0800
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-31 12:34 +1300
                Re: Octal BartC <bc@freeuk.com> - 2016-12-30 23:40 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-30 22:12 +0000
                Re: Octal raltbos@xs4all.nl (Richard Bos) - 2016-12-28 21:38 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 12:04 +0000
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-29 13:42 +0100
                Re: Octal Ian Collins <ian-news@hotmail.com> - 2016-12-30 08:59 +1300
                Re: Octal supercat@casperkitty.com - 2016-12-29 12:23 -0800
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-30 10:56 +0100
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 22:09 +0000
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-29 12:27 +0100
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 21:18 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 20:46 +0000
                Re: Octal raltbos@xs4all.nl (Richard Bos) - 2016-12-28 20:55 +0000
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-28 14:54 -0600
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 15:44 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 19:39 +0000
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-28 15:04 -0600
                Re: Octal raltbos@xs4all.nl (Richard Bos) - 2016-12-28 19:52 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-29 09:36 -0800
                Re: Octal BartC <bc@freeuk.com> - 2016-12-29 18:02 +0000
                Re: Octal BartC <bc@freeuk.com> - 2016-12-30 16:17 +0000
                Re: Octal David Brown <david.brown@hesbynett.no> - 2017-01-01 16:09 +0100
                Re: Octal BartC <bc@freeuk.com> - 2016-12-28 20:02 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 12:32 -0800
                Re: Octal Richard Heathfield <rjh@cpax.org.uk> - 2016-12-29 13:45 +0000
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-28 17:16 +0000
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 10:04 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-02 02:26 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2017-01-02 12:35 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-12 23:22 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2017-01-13 10:04 -0800
                Re: Octal Tim Rentsch <txr@alumni.caltech.edu> - 2017-01-14 00:45 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 09:59 -0800
                Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-27 09:45 -0800
        Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-27 17:14 +0100
          Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-27 08:23 -0800
            Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-28 10:37 +0100
              Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-28 03:07 -0800
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-28 12:25 +0100
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-28 11:58 +0000
                Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-28 04:35 -0800
                Re: Octal Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-28 17:31 +0000
                Re: Octal "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2016-12-28 09:38 -0800
                Re: Octal Robert Wessel <robertwessel2@yahoo.com> - 2016-12-28 15:12 -0600
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 12:01 -0800
              Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 09:20 -0800
                Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-28 13:39 -0800
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-29 12:29 +0100
                Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-28 22:20 +0100
      Re: Octal Noob <root@127.0.0.1> - 2016-12-28 13:02 +0100
        Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-28 13:30 +0100
        Re: Octal BartC <bc@freeuk.com> - 2016-12-28 13:25 +0000
  Re: Octal Manfred <noname@invalid.add> - 2016-12-27 15:19 +0100
    Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 08:37 -0800
      Re: Octal Manfred <noname@invalid.add> - 2016-12-27 18:43 +0100
        Re: Octal Keith Thompson <kst-u@mib.org> - 2016-12-27 12:07 -0800
    Re: Octal Manfred <noname@invalid.add> - 2016-12-27 18:21 +0100
  Re: Octal David Brown <david.brown@hesbynett.no> - 2016-12-27 15:28 +0100
  Re: Octal BGB <cr88192@hotmail.com> - 2016-12-27 11:42 -0600

csiph-web