Re: bart again (UCX64)

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: bart again (UCX64)
Date	2023-09-06 18:47 -0700
Organization	None to speak of
Message-ID	<87ledi3gbt.fsf@nosuchdomain.example.com> (permalink)
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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>> Bart <bc@freeuk.com> writes:
>> [...]
>>>> I assume GNU C allows semicolons after function definitions. That's
>>>> unfortunate. If the grammar rule was applied strictly, then there would be
>>>> no programs in existence that would use semicolons like that.
>>
>> Just to be clear, a semicolon after a function definition:
>>
>>     void foo(void) {};
>>
>> isn't associated with the function definition.  The semicolon is treated
>> as a file-scope declaration.  If the above is valid, then so is a
>> source file consisting of a single line with just a semicolon.
>>
>>> K&R C allowed it, mainly because a type-specifier can be omitted and
>>> defaults to int.  The /grammar/ in K&R does not permit it, but the text
>>> says that, if the type-specifier is missing it is taken to be int.
>> [...]
>>
>> So K&R C (and C90?) treated this:
>
> Not C90 as far as I know.

You're right.

>>     ;
>>
>> at file scope as a definition with an implicit type of int, so it's
>> equivalent to this:
>>
>>     int;
>
> Probably, though it's hard to tell if that is "equivalent" since there
> are no observable facts.  A K&R C Unix V7 compiler running on a PDP11
> simulator accepts this code silently:
>
>   ;
>   int;
>   int main(){ return 1; };
>
> K&R1 says that both the type specifier and the storage class specifier
> can be omitted, and that int is assumed when no type is given.  When the
> storage class is missing it is assumed to be auto in a function and
> extern outside, with the exception that function are never automatic.

Right.  What I was wondering about is which rule makes
    int;
at file scope invalid -- and I think I've found the answer.

C90 6.5 has this syntax:
    declaration
        declaration-specifiers init-declarator-list[opt] ;
with this constraint:
     A declaration shall declare at least a declarator, a tag, or the
     members of an enumeration.
The wording in later editions is similar.  K&R1 did not have that
constraint.

So `int;` satisfies the syntax of a declaration, but violates the
constraint.

The *init-declarator-list* is optional so you can have declarations
like:
    enum foo { x, y };
Both `enum foo { x, y }` and `int` are type specifiers; the former is
allowed by itself in a declaration, but the latter is not.

Getting back to the original issue, I think that gcc's acceptance of a
lone semicolon at file scope goes back to K&R C, which allowed it; the
old "implicit int" rule made it equivalent to `int;`, which was allowed
because the constraint I mentioned above had not yet been introduced.

It would IMHO have been reasonable for gcc to make this invalid by
default.  Of course it rejects it if you ask for conformance.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */

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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) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 00:56 +0000
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 00:47 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-09 18:49 +0200
                Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-09 10:27 -0700
                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) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:07 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-09 18:51 +0200
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 16:35 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:04 +0000
        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

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