Date: Wed, 29 Oct 1997 15:57:42 -0700 (MST)
From: firewind <firewind AT metroid DOT dyn DOT ml DOT org>
To: Peter Palotas <blizzar AT hem1 DOT passagen DOT se>
cc: djgpp AT delorie DOT com
Subject: Re: Reading the command line
In-Reply-To: <3.0.16.19971029215033.35b7c09c@hem1.passagen.se>
Message-ID: <Pine.LNX.3.95.971029154836.227A-100000@metroid.dyn.ml.org>
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On Wed, 29 Oct 1997, Peter Palotas wrote:

> At 07.06 1997-10-29 GMT, you wrote:
> >If you allow 'void main()' to be valid, you also allow 'if(1 + 1 == 3)' to be
> >a true comparison.
> >
> >The standard says main() shall return int, and so int it shall return.
> 
> If this is so, why doesn't the compiler generate an error for declaring
> main() as 'void main()'?

It works accidentally on some compilers (the DOS version of gcc, for
example) and as an extension to the language on others (other popular DOS
compilers, for example). In comp.lang.c, it has been brought up that some
compilers (I think it was an HP\UX compiler, although I can't recall) *do*
in fact flag 'void main()' as an error.

The reason gcc does not vomit on 'void main()' (but it should, imho) is
because the standard does not require it to. The standard says 'int
main()' or 'int main(int argc, char *argv[])' (and 'int main(int argc,
char **argv)' by congruence) are valid types for 'main.' Other
declarations of main() invoke *undefined behavior*. The compiler can
accept it, the compiler can vomit, the compiler can erase your hard drive,
the compiler can print 'READ THE STANDARD, FOOL' fifty thousand times on
your screen, and any of these are valid according to the standard.

In other words, expecting 'void main' to work is just about as foolish as
expecting 'a[i++] = i++;' to yield a predictable result. This (modifying 
and using a variable more than once without a sequence point) is also 
undefined behavior, and the compiler is not required to (but can!) refuse
to accept it.

If you would like more and detailed discussion of why 'void main' is
illegal, and why some people refuse to let go of it, there have been
several threads of this topic going on in comp.lang.c. See DejaNews.

[-                               firewind                                   -]
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