Date: Fri, 30 Oct 1998 08:03:14 +1100 From: Peter Jeremy <peter.jeremy@auss2.alcatel.com.au> To: hackers@FreeBSD.ORG Cc: luigi@labinfo.iet.unipi.it Subject: Re: compiler prototype question... Message-ID: <98Oct30.080247est.40341@border.alcanet.com.au>
next in thread | raw e-mail | index | archive | help
On Thu, 29 Oct 1998 05:53:44 +0100 (MET), Luigi Rizzo <luigi@labinfo.iet.unipi.it> wrote:
>can someone tell me why in the following C program:
>
> int c1 (int c);
> int c1 (char c) { return 1 ; }
> proto.c:8: conflicting types for `c1'
> proto.c:7: previous declaration of `c1'
Here, you've specified conflicting prototypes. The declaration states that
c1 takes a single `int' argument, whilst the definition states that it
takes a single `char' argument.
> int c2 (int c);
> int c2 (c) char c; { return 1 ; }
This is correct. A K&R definition means that the argument will be
promoted: {char,short}->int, float->double. The prototype therefore
matches the definition. Note that although the argument is passed as
an int, it is referenced as a char. The remaining bytes are ignored.
> int c3 (char c);
> int c3 (c) int c; { return 1 ;}
> proto.c: In function `c3':
> proto.c:14: argument `c' doesn't match prototype
> proto.c:13: prototype declaration
Here, you've specified conflicting prototypes. The declaration states that
c1 takes a single `char' argument, whilst the definition states that it
takes a single `int' argument.
> int c4 (char c);
> int c4 (int c) { return 1 ;}
> proto.c:17: conflicting types for `c4'
> proto.c:16: previous declaration of `c4'
This is identical to c3.
>To me, c2() seems as bad as the others, and i don't understand why
>the compiler does not complain.
This is according to the ANSI standard rules.
> It seems that when the prototype
>declares an "int" argument, then any signed/unsigned type is accepted
>for that argument in the non-ansi function body.
Any char, short or int argument is acceptable. long isn't and I'd
need to check on unsigned.
> As you can imagine
>this defeats the usefulness of prototypes and obfuscates code.
Not true. It complies with the K&R C calling conventions.
Peter
--
Peter Jeremy (VK2PJ) peter.jeremy@alcatel.com.au
Alcatel Australia Limited
41 Mandible St Phone: +61 2 9690 5019
ALEXANDRIA NSW 2015 Fax: +61 2 9690 5247
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?98Oct30.080247est.40341>