NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/std/c/224

Internet Message Format | 1996-08-06 | 4KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c,comp.std.c
Subject: Re: Integral conversion e.t.c. (was: Re: Hungarian notation)
Date: Mon, 29 Jan 96 23:37:46 GMT
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In article <[e-mail]>
           [e-mail] "James Kanze US/ESC 60/3/141 #40763" writes:

>I think the crux of Michael Furman's question lies therein.  Does the
>standard require a diagnostic if the function main is not of one of
>the two types given?

No, that is neither a syntax error (or at least need not be) or a violation
of a rule in a constraints section so no diagnostic is required.

>To tell the truth, I'm not sure what the answer is.  The text
>concerning main is in the chapter describing the environment.  It
>doesn't appear as a semantic restriction or anything.  It simply
>states that on start-up, a function called main will be called, and
>that the implementation must support the following forms.  It doesn't
>seem (to me, at least) to say anything about what other forms it might
>support, or what the implementation must do if given a fully other
>definition of main.

The standard defines the behaviour of 2 stated forms of main (and
semantically equivalent forms). It doesn't define any behaviour for any
other forms therefore those other forms result in undefined behaviour -
from 3.16:

"If a ``shall'' or ``shall not'' requirement that appears outside of
 a constraint is violated, the behaviour is undefined. Undefined behaviour
 is otherwise indicated by the words ``undefined behaviour'' or by the
 omission of any explicit definition of behaviour. There is no difference
 in emphasis among these three; they all describe ``behaviour that is
 undefined''".

Other forms of main are an example of "omission of any explicit definition
of behaviour" and by the last sentence have the same effect as any other
form of undefined behaviour.

>Normally, I would expect (at the very least) a compiler to generate a
>warning or an error for a main that it did not support.

There is no requirement for that. Indeed that allows useful implementation
extensions without making the compiler non-conforming. Of course such
extensions are non-portable.

>In fact,
>however, my compiler (gcc) accepts the following definition without
>the slightest complaint, although I'd rather not think about what will
>happen when I access parameter d:
>
>        int main( char a , int b , long c , double d )

main is something that the language leaves up to the programmer to get
right.

>|> For purposes of the C newsgroups, discussion of what is/isn't legal
>|> is generally restricted to strictly conforming C.
>
>Yes and no.  In comp.std.c, the discussion is exactly about what is
>legal according to the standard.  In comp.lang.c (to which this
>article is also cross-posted), the discussion should generally be a
>bit more open.
>
>Thus, for example, in comp.std.c, a program with a variable named far
>is illegal, and that is it.

I assume that was a typo (or thinko!) for "legal".

>In comp.lang.c (and I hope in its
>moderated variant), I would hope that someone would point out that,
>legal or not, it's going to get you into trouble.

Makes sense.

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
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