Date: Tue, 18 Dec 2001 10:36:32 +0100 From: Erik Trulsson <ertr1013@student.uu.se> To: Mark Murray <mark@grondar.za> Cc: John Baldwin <jhb@FreeBSD.org>, "David O'Brien" <obrien@FreeBSD.org>, cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org, Luigi Rizzo <rizzo@aciri.org>, Garance A Drosihn <drosih@rpi.edu> Subject: Re: Are prototypes for main() illegal by any standard ? (was Re: Message-ID: <20011218093631.GA1096@student.uu.se> In-Reply-To: <200112180848.fBI8mvO00685@grimreaper.grondar.org> References: <XFMail.011216160443.jhb@FreeBSD.org> <200112180848.fBI8mvO00685@grimreaper.grondar.org>
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On Tue, Dec 18, 2001 at 10:48:56AM +0200, Mark Murray wrote:
> > > This is comming up due to a bug in a single compiler. We have fixed that
> > > compiler. AFAIK the other two compilers we use at all today -- TenDRA
> > > and Compaq's compiler does not have this bug. So why change all this
> > > code when we fixed things at the source of the problem?
> >
> > Agreed. Requesting prototypes for main is the compiler bug, not hiding the
> > warning for main.
>
> This I do not understand. :-)
>
> AFAIK, this is perfectly legal C:
Not quite.
>
> /* begin */
> void printf(char *, ...)
Since you did not #include <stdio.h> I guess you get away with this.
(Most library functions are not reserved unless the relevant header is
included.)
>
> void main(void)
main should always return an int.
> {
> printf("Hello world");
> }
> /* end */
You haven't defined the 'printf' anywhere.
If you want to use the standard printf function you need to include
<stdio.h>
>
> And it should compile warning-free and run without error. Agreed
No it should not.
> that the style sucks, but it is _legal_ - and any compiler's prior
> assumed knowledge about main is plain wrong - it is a linker thing
> to use ``main'' as an entry point, and nobody else's damn business
> what it is after that! (argc and argv are likewise conventions that
> are less useful in an embedded environment with no shell (ya, ya I
> know about execv :)).
>
> Now if anyone can show official standards showing me that I'm
> wrong here, I'll shut up and back off. :-)
The C standard does not make a distinction between compiler and linker,
nor should it.
A compiler is allowed to have a lot of knowledge about the standard
functions.
For a hosted environment it has the following to say about main:
(From a draft for the C99 standard)
5.1.2.2.1 Program startup
[#1] The function called at program startup is named main.
The implementation declares no prototype for this function.
It shall be defined with a return type of int and with no
parameters:
int main(void) { /* ... */ }
or with two parameters (referred to here as argc and argv,
though any names may be used, as they are local to the
function in which they are declared):
int main(int argc, char *argv[]) { /* ... */ }
For a freestanding environment (which can be useful for embedded stuff)
you don't have any requirements on main(). OTOH about 95% of the
standard library is not guaranteed to be available either.
The only header files which may be included in a strictly program for a
freestanding implementation are
<float.h>, <iso646.h>, <limits.h>, <stdarg.h>, <stdbool.h>,
<stddef.h>, and <stdint.h>
--
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se
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