Re: C++ forcing unnecessary changes to C?

Path	csiph.com!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: C++ forcing unnecessary changes to C?
Date	Fri, 25 Nov 2016 12:30:00 -0800
Organization	None to speak of
Lines	44
Message-ID	<ln7f7rb8vr.fsf@kst-u.example.com> (permalink)
References	<o0mseq$e7o$1@dont-email.me> <o0n769$kth$1@dont-email.me> <o0n92n$t5k$1@dont-email.me> <o0nc67$8dh$1@dont-email.me> <faf53chagnm148n9jr0dc1a459ucos4rg2@4ax.com> <o115k5$84f$1@dont-email.me> <ef0g3cpbude8eivf8ve31aeqdgecemjs61@4ax.com>
Mime-Version	1.0
Content-Type	text/plain; charset=utf-8
Content-Transfer-Encoding	8bit
Injection-Info	mx02.eternal-september.org; posting-host="3c5e60c3a5e134696d7a5f0d024ade78"; logging-data="28230"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/Tidxwll4iOUU/90e1HaUX"
User-Agent	Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)
Cancel-Lock	sha1:kCsP8vATS2JmxizHh1psqFnpej8= sha1:aPneiJ8wUENZ/ZNao6jOJbwGVXs=
Xref	csiph.com comp.lang.c:97478

Show key headers only | View raw

Robert Wessel <robertwessel2@yahoo.com> writes:
> On Tue, 22 Nov 2016 11:11:52 +0100, jacobnavia
> <jacob@jacob.remcomp.fr> wrote:
>>Le 21/11/2016 à 10:26, Robert Wessel a écrit :
>>> Falling off the end of main() without a return was legal in C89, but
>>> the actual value returned to the environment was undefined.
>>
>>Any sensible compiler would complain since returning from a function 
>>that should return a value without assigning the return value is always 
>>an error.
>
> No, the point is that C89 makes a special dispensation (5.1.2.2.3) for
> main() (only in a hosted environment, and for no other function), so
> that falling off the end of main() without a return is *not* an error.
> At least from a standard's perspective.  It's darn bad practice, of
> course.

It depends on what you mean by "an error".  It is neither a constraint
violation nor undefined behavior.

C89 had no section 5.1.2.2.3; that's from the equivalent but renumbered
ISO C90 standard.  (It would have been 2.1.2.2.3 in the ANSI C89
standard.)

What that section says is that

    If the main function executes a return that specifies no value, the
    termination status returned to the host environment is undefined.

6.6.6.4 says that reaching the closing "}" is equivalent to a "return;".

Falling off the end of *any* function without returning a value is not
an error in C89/C90.  It's only attempting to use the result that has
undefined behavior.  C99 and C11 keep that rule; a "return;" with no
value is forbidden in a non-void function, but it's still legal (but a
bad idea) to fall off the end.

[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

C++ forcing unnecessary changes to C? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-18 20:34 +0800
  Re: C++ forcing unnecessary changes to C? Thiago Adams <thiago.adams@gmail.com> - 2016-11-18 05:09 -0800
    Re: C++ forcing unnecessary changes to C? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-18 21:42 +0800
      Re: C++ forcing unnecessary changes to C? jameskuyper@verizon.net - 2016-11-18 11:14 -0800
    Re: C++ forcing unnecessary changes to C? jameskuyper@verizon.net - 2016-11-18 11:10 -0800
      Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-19 15:26 +0100
        Re: C++ forcing unnecessary changes to C? "James R. Kuyper" <jameskuyper@verizon.net> - 2016-11-19 10:09 -0500
          Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-20 13:47 +0100
      Re: C++ forcing unnecessary changes to C? Thiago Adams <thiago.adams@gmail.com> - 2016-11-21 03:25 -0800
        Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-21 14:15 +0100
          Re: C++ forcing unnecessary changes to C? Thiago Adams <thiago.adams@gmail.com> - 2016-11-21 05:39 -0800
  Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-18 14:26 +0100
    Re: C++ forcing unnecessary changes to C? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-18 21:41 +0800
      Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-18 15:20 +0100
        Re: conduct in comp.lang.c "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-18 22:23 +0800
  Re: C++ forcing unnecessary changes to C? Philipp Klaus Krause <pkk@spth.de> - 2016-11-18 15:16 +0100
    Re: C++ forcing unnecessary changes to C? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-18 22:20 +0800
      Re: C++ forcing unnecessary changes to C? jameskuyper@verizon.net - 2016-11-18 11:18 -0800
    Re: C++ forcing unnecessary changes to C? supercat@casperkitty.com - 2016-11-18 07:15 -0800
      Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-18 16:55 +0100
        Re: C++ forcing unnecessary changes to C? supercat@casperkitty.com - 2016-11-18 08:31 -0800
          Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-18 17:38 +0100
  Re: C++ forcing unnecessary changes to C? John Bode <jfbode1029@gmail.com> - 2016-11-18 07:09 -0800
    Re: C++ forcing unnecessary changes to C? Thiago Adams <thiago.adams@gmail.com> - 2016-11-18 07:22 -0800
      Re: C++ forcing unnecessary changes to C? Thiago Adams <thiago.adams@gmail.com> - 2016-11-18 07:31 -0800
        Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-18 17:04 +0100
  Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-18 16:37 +0100
    Re: C++ forcing unnecessary changes to C? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-18 23:53 +0800
    Re: C++ forcing unnecessary changes to C? supercat@casperkitty.com - 2016-11-18 08:00 -0800
      Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-18 17:34 +0100
      Re: C++ forcing unnecessary changes to C? Keith Thompson <kst-u@mib.org> - 2016-11-18 09:32 -0800
    Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-18 17:09 +0100
      Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-18 18:02 +0100
        Re: C++ forcing unnecessary changes to C? Robert Wessel <robertwessel2@yahoo.com> - 2016-11-21 03:26 -0600
          Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-22 11:11 +0100
            Re: C++ forcing unnecessary changes to C? jameskuyper@verizon.net - 2016-11-22 08:55 -0800
            Re: C++ forcing unnecessary changes to C? Robert Wessel <robertwessel2@yahoo.com> - 2016-11-25 03:25 -0600
              Re: C++ forcing unnecessary changes to C? supercat@casperkitty.com - 2016-11-25 10:00 -0800
              Re: C++ forcing unnecessary changes to C? Keith Thompson <kst-u@mib.org> - 2016-11-25 12:30 -0800
                Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-26 00:38 +0100
                Re: C++ forcing unnecessary changes to C? supercat@casperkitty.com - 2016-11-26 10:44 -0800
                Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-26 20:44 +0100
                Re: C++ forcing unnecessary changes to C? supercat@casperkitty.com - 2016-11-26 12:38 -0800
                Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-26 21:00 +0100
  Re: C++ forcing unnecessary changes to C? jameskuyper@verizon.net - 2016-11-18 11:04 -0800
    Re: [OT] discipline and obedience "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-19 22:53 +0800
    Re: C & C++ Committee "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-19 22:55 +0800
      Re: C & C++ Committee jameskuyper@verizon.net - 2016-11-19 08:02 -0800
        Re: C & C++ Committee "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-20 00:09 +0800
          Re: C & C++ Committee jameskuyper@verizon.net - 2016-11-19 08:35 -0800
            Re: C & C++ Committee fir <profesor.fir@gmail.com> - 2016-11-19 08:51 -0800
              Re: Do you write C programs? "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-20 01:00 +0800
            Re: C & C++ Committee "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-11-20 00:59 +0800
  Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-22 11:14 +0100
    Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-22 12:05 +0100
      Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-22 14:51 +0100
        Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-22 15:50 +0100
          Re: C++ forcing unnecessary changes to C? BartC <bc@freeuk.com> - 2016-11-22 15:01 +0000
            Re: C++ forcing unnecessary changes to C? Keith Thompson <kst-u@mib.org> - 2016-11-22 08:58 -0800
              Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-22 18:08 +0100
              Re: C++ forcing unnecessary changes to C? BartC <bc@freeuk.com> - 2016-11-22 18:14 +0000
                Re: C++ forcing unnecessary changes to C? Ian Collins <ian-news@hotmail.com> - 2016-11-23 08:33 +1300
                Re: C++ forcing unnecessary changes to C? BartC <bc@freeuk.com> - 2016-11-22 19:42 +0000
                Re: C++ forcing unnecessary changes to C? Ian Collins <ian-news@hotmail.com> - 2016-11-23 08:51 +1300
                Re: C++ forcing unnecessary changes to C? Keith Thompson <kst-u@mib.org> - 2016-11-22 12:13 -0800
                Re: C++ forcing unnecessary changes to C? BartC <bc@freeuk.com> - 2016-11-22 21:35 +0000
                Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-23 00:47 +0100
                Re: C++ forcing unnecessary changes to C? Keith Thompson <kst-u@mib.org> - 2016-11-22 12:09 -0800
                Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-23 00:40 +0100
                Re: C++ forcing unnecessary changes to C? jacobnavia <jacob@jacob.remcomp.fr> - 2016-11-26 01:27 +0100
                Re: C++ forcing unnecessary changes to C? David Brown <david.brown@hesbynett.no> - 2016-11-26 01:48 +0100
              Re: C++ forcing unnecessary changes to C? Nathan Wagner <nw@hydaspes.if.org> - 2016-11-24 18:09 +0000

csiph-web