Re: bart again (UCX64)

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.c
Subject	Re: bart again (UCX64)
Date	2023-09-06 03:04 +0100
Organization	A noiseless patient Spider
Message-ID	<87v8coqcpa.fsf@bsb.me.uk> (permalink)
References	(16 earlier) <ud4a6a$1d4cd$1@dont-email.me> <87edjeujqw.fsf@bsb.me.uk> <ud5gkt$1kj5t$1@dont-email.me> <87tts9sbo8.fsf@bsb.me.uk> <b9e00c9c-e879-49d2-a00a-05256b87d766n@googlegroups.com>

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Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:

> On Tuesday, 5 September 2023 at 01:31:48 UTC+1, Ben Bacarisse wrote:
>> 
>> > Do you have your own examples in other languages which do the same: return 
>> > whatever garbage is in a register, since the language allows you to omit an 
>> > explicit value?
>> If "the language" is C, then it does not allow any such thing. And the 
>> program you posted does not "do" anything. It is as meaningless and any 
>> and all other undefined C programs. 
>> 
> Originally C didn't have a void type. So 
>
> if (foo())
>
> was always a legitimate statement.

For some values of "legitimate".  It's never been legitimate in the
sense of "being in accordance with established or accepted rules" when
foo does not return a value determined by the programmer.  The accepted
rules of programming include not making a choice based on garbage data.

It is syntactically legitimate, but using the term unqualified could
suggest to readers that it was once a reasonable thing to write.

> If foo() couldn't sensibly return a value, then it would default to
> int, and ...

If foo() couldn't sensibly return a value, then the programmer would
usually omit the return type as a hint to the reader.  Since missing
types defaulted to int ...

> ... whatever garbage was in the register used for passing back
> values would be used.  This wasn't ideal, but it probably made the
> very primitive first compilers easier to write.
>
> It's hung on to the present day.

What's the "it" refer to?  Neither the default int rule nor returning
whatever is in a particular register could be taken to apply anymore.
The rule has changed, and modern compilers don't always behave that
predictably.  Optimisation, in particular, is likely to make the
behaviour quite different.

> Compilers will still accept functions which return
> garbage values. Presumably for backwards compatibility,

I suspect it's also because detecting the cases that are actual errors
is hard and expecting people to sometimes add junk return statements is
less than ideal.  Modern compilers can detect lots of the cases and can
be told to reject such programs which make the problem much less
significant (for people who are prepared to use compiler flags).

> though as some people have
> pointed out, in some case you would have to add dummy returns on control paths
> which couldn't in fact be followed, to help the compiler out.

-- 
Ben.

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Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-01 21:09 +0000
  Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-01 22:41 +0100
    Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-01 22:34 +0000
      Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-01 15:51 -0700
      Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-02 14:06 +0100
        Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-02 17:27 +0000
    Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-01 16:02 -0700
      Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-02 01:50 +0100
        Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-02 01:12 +0000
          Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-01 19:13 -0700
          Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-02 11:57 +0100
            Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-02 18:19 +0200
              Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-02 19:53 +0100
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-03 06:32 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-03 16:02 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-03 18:11 +0100
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-03 11:31 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-03 20:07 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-03 22:08 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-04 03:16 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-04 10:54 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-04 11:06 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-04 14:54 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-04 22:02 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-05 01:31 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-05 02:24 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-06 04:29 +0100
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-05 21:06 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-06 01:03 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-06 20:58 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-06 19:21 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-07 20:18 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-06 13:07 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-06 22:41 +0100
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-06 15:56 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-07 00:53 +0100
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-06 18:47 -0700
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-06 17:25 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-04 18:30 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-06 03:04 +0100
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-06 21:48 -0700
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-07 06:10 +0000
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-07 02:06 -0700
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-07 15:52 +0000
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 14:18 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-07 15:28 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-07 16:54 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-07 17:02 +0100
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-07 16:12 +0000
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 16:17 +0000
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-07 17:37 +0100
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 14:51 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 00:46 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 11:06 +0200
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 10:19 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-07 15:55 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 15:16 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-07 17:02 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 16:15 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-07 17:51 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 17:24 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-07 21:53 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 21:34 +0000
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 17:25 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-07 21:37 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 21:02 +0000
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 16:14 -0700
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 16:09 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-07 17:34 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-07 17:22 +0000
                Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-07 11:44 -0700
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 15:16 -0700
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-07 23:48 +0100
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 17:16 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 11:16 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-08 10:51 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 13:00 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-08 13:05 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 16:11 +0200
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-08 05:03 -0700
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-08 13:39 +0100
                Re: bart again (UCX64) candycanearter07 <no@thanks.net> - 2023-09-08 07:49 -0500
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-04 14:14 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-04 16:59 +0200
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-04 15:41 -0700
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-04 18:15 -0700
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-04 18:57 -0700
            Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-02 17:10 +0000
              Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-02 13:13 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-02 22:50 +0100
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-02 14:54 -0700
        Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-01 19:02 -0700
        Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-02 22:42 +0100
          Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-02 15:08 -0700
            Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-03 02:00 +0100
          Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-02 23:18 +0100
            Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-03 02:28 +0100
              Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-03 06:58 +0000
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-03 15:52 +0100
              Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-03 11:02 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-03 16:25 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-03 16:49 +0100
              Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-03 16:16 +0200
      Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-02 18:11 +0200
        Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-02 22:08 +0100
          Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-03 16:48 +0200
        Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-02 14:52 -0700
          Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-03 02:23 -0700
            Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-03 03:47 -0700
            Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-03 18:44 +0000
              Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-03 18:01 -0700
          Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-03 16:59 +0200
          Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-03 17:50 -0700

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