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Re: Type system protocols rest atop fundamental data

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From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: Type system protocols rest atop fundamental data
Date Thu, 15 Jun 2017 09:27:18 -0700
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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> bartc <bc@freeuk.com> writes:
> <snip>
>> Give me an example of a freely available C compiler (other than DMC
>> which is the only line that notices the mismatched arguments), which
>> out of the box and with default options, diagnoses:
>>
>>   randommadeupfunction(1,2,3,"blah");
>>   randommadeupfunction(1e37);
>>
>> as an error.
>
> You need to say a bit more for that even to be an error.  In C90 and up
> a declaration can make those lines correct (though not necessarily very
> useful) and in K&R C they are OK without one.  Only in C90 code with no
> declaration in scope is this definitely an error.

Given this complete translation unit:

int main(void) {
    randommadeupfunction(1,2,3,"blah");
    randommadeupfunction(1e37);
}

In C90, it violates no constraint or syntax rule, and no diagnostic is
required, but the behavior is undefined.  Both calls implicitly create
the same declaration in the enclosing block:

    int randommadeupfunction();

which is consistent with both calls, but there is no possible
*definition* of the function that would give both calls defined
behavior.

(Yes, this is an ugly and error-prone language feature, which is why
it's no longer in the language.)

You can even add a prototype that makes the entire translation unit
valid, and without undefined behavior if the function is defined
appropriately elsewhere:

int main(void) {
    void randommadeupfunction(double, ...);
    randommadeupfunction(1,2,3,"blah");
    randommadeupfunction(1e37);
}

On the first call, the initial argument is implicitly converted from int
to double.  A more apt example might have passed a string literal as the
first argument in the first call, and a floating constant in the second;
then no variadic prototype could make both calls valid.

[...]

-- 
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"

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Thread

Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-14 06:14 -0700
  Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-14 06:18 -0700
    Re: Type system protocols rest atop fundamental data mark.bluemel@gmail.com - 2017-06-14 08:00 -0700
      Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-14 08:06 -0700
    Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-14 20:39 +0100
      Re: Type system protocols rest atop fundamental data Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-14 21:51 +0100
        Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-14 22:25 +0100
          Re: Type system protocols rest atop fundamental data Keith Thompson <kst-u@mib.org> - 2017-06-14 14:37 -0700
            Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-15 00:32 +0100
              Re: Type system protocols rest atop fundamental data Keith Thompson <kst-u@mib.org> - 2017-06-14 17:02 -0700
                Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-15 01:34 +0100
                Re: Type system protocols rest atop fundamental data Robert Wessel <robertwessel2@yahoo.com> - 2017-06-14 20:28 -0500
                Re: Type system protocols rest atop fundamental data raltbos@xs4all.nl (Richard Bos) - 2017-06-18 10:49 +0000
                Re: Type system protocols rest atop fundamental data Keith Thompson <kst-u@mib.org> - 2017-06-14 20:02 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-15 10:29 +0200
                Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-15 10:54 +0100
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-15 13:15 +0200
                Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-15 13:51 +0100
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-15 16:13 +0200
                Re: Type system protocols rest atop fundamental data Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-15 16:01 +0100
                Re: Type system protocols rest atop fundamental data Keith Thompson <kst-u@mib.org> - 2017-06-15 09:27 -0700
                Re: Type system protocols rest atop fundamental data raltbos@xs4all.nl (Richard Bos) - 2017-06-18 10:49 +0000
                Re: Type system protocols rest atop fundamental data Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-16 23:35 -0700
                Re: Type system protocols rest atop fundamental data Keith Thompson <kst-u@mib.org> - 2017-06-17 16:10 -0700
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-17 19:23 -0700
              Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-16 13:13 +1200
                Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-15 18:44 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-16 13:42 +0200
                Re: Type system protocols rest atop fundamental data Gareth Owen <gwowen@gmail.com> - 2017-06-16 20:20 +0100
                Re: Type system protocols rest atop fundamental data Robert Wessel <robertwessel2@yahoo.com> - 2017-06-18 00:32 -0500
                Re: Type system protocols rest atop fundamental data raltbos@xs4all.nl (Richard Bos) - 2017-06-18 11:06 +0000
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-18 15:26 +0200
                Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-18 14:58 +0100
          Re: Type system protocols rest atop fundamental data Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-15 01:42 +0100
            Re: Type system protocols rest atop fundamental data bartc <bc@freeuk.com> - 2017-06-15 11:52 +0100
              Re: Type system protocols rest atop fundamental data Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-15 16:07 +0100
                Re: Type system protocols rest atop fundamental data Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-16 23:37 -0700
              Re: Type system protocols rest atop fundamental data Keith Thompson <kst-u@mib.org> - 2017-06-15 09:52 -0700
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-15 10:36 -0700
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-15 17:58 +0000
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-15 11:48 -0700
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-15 19:01 +0000
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-15 12:29 -0700
                Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-16 13:47 +1200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-15 19:33 -0700
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-15 13:02 -0700
                Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-15 13:09 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-15 22:25 +0200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-15 14:23 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-15 23:53 +0200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-15 15:39 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-16 13:50 +0200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-16 08:40 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-18 16:49 +0200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-19 10:33 -0700
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-19 17:50 +0000
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-19 12:12 -0700
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-19 19:27 +0000
                Re: Type system protocols rest atop fundamental data Ike Naar <ike@iceland.freeshell.org> - 2017-06-20 15:18 +0000
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-20 09:30 -0700
                Re: Type system protocols rest atop fundamental data David Kleinecke <dkleinecke@gmail.com> - 2017-06-16 12:05 -0700
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-16 12:30 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-18 16:54 +0200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-19 13:25 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-20 09:27 +0200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-20 08:53 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-20 22:12 +0200
                Re: Type system protocols rest atop fundamental data "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-06-20 13:14 -0700
                Re: Type system protocols rest atop fundamental data "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-06-20 13:16 -0700
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-20 14:04 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-21 15:33 +0200
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-20 13:25 +0000
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-16 19:42 +0000
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-18 16:58 +0200
                Re: Type system protocols rest atop fundamental data raltbos@xs4all.nl (Richard Bos) - 2017-06-17 19:18 +0000
                Re: Type system protocols rest atop fundamental data Robert Wessel <robertwessel2@yahoo.com> - 2017-06-15 23:40 -0500
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-16 13:51 +0200
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-16 12:55 +0000
      Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-14 14:23 -0700
        Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-16 13:48 +1200
          Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-15 19:03 -0700
            Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-16 15:12 +1200
              Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-15 20:20 -0700
              Re: Type system protocols rest atop fundamental data Richard Heathfield <rjh@cpax.org.uk> - 2017-06-16 07:03 +0100
                Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-16 20:01 +1200
                Re: Type system protocols rest atop fundamental data Richard Heathfield <rjh@cpax.org.uk> - 2017-06-16 19:21 +0100
                Re: Type system protocols rest atop fundamental data "Chris M. Thomasson" <invalid@invalid.invalid> - 2017-06-16 12:07 -0700
                Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-17 16:18 +1200
                Re: Type system protocols rest atop fundamental data Richard Heathfield <rjh@cpax.org.uk> - 2017-06-17 07:19 +0100
                Re: Type system protocols rest atop fundamental data raltbos@xs4all.nl (Richard Bos) - 2017-06-17 19:19 +0000
                Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-18 08:29 +1200
                Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-17 18:49 -0700
                Re: Type system protocols rest atop fundamental data Ian Collins <ian-news@hotmail.com> - 2017-06-18 16:18 +1200
                Re: Type system protocols rest atop fundamental data Öö Tiib <ootiib@hot.ee> - 2017-06-18 06:28 -0700
                Re: Type system protocols rest atop fundamental data Keith Thompson <kst-u@mib.org> - 2017-06-16 09:11 -0700
                Re: Type system protocols rest atop fundamental data Tim Rentsch <txr@alumni.caltech.edu> - 2017-06-16 23:37 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-18 17:04 +0200
            Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-16 12:56 +0000
              Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-16 07:10 -0700
              Re: Type system protocols rest atop fundamental data GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-06-16 16:38 +0200
                Re: Type system protocols rest atop fundamental data scott@slp53.sl.home (Scott Lurndal) - 2017-06-16 15:02 +0000
                Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-16 08:11 -0700
                Re: Type system protocols rest atop fundamental data David Brown <david.brown@hesbynett.no> - 2017-06-18 17:13 +0200
      Re: Type system protocols rest atop fundamental data supercat@casperkitty.com - 2017-06-14 14:42 -0700
  Re: Type system protocols rest atop fundamental data Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-06-14 21:32 +0100
    Re: Type system protocols rest atop fundamental data "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2017-06-14 14:28 -0700

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