Date: Wed, 2 Mar 2005 19:17:52 +0200 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: Florian Hengstberger <e0025265@student.tuwien.ac.at> Cc: freebsd-questions@freebsd.org Subject: Re: c standard Message-ID: <20050302171752.GA5229@orion.daedalusnetworks.priv> In-Reply-To: <icqfqw.8f29so@webmail.tuwien.ac.at> References: <icqfqw.8f29so@webmail.tuwien.ac.at>
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On 2005-03-02 17:13, Florian Hengstberger <e0025265@student.tuwien.ac.at> wrote:
> Following is possible with gcc and g++:
>
> #include <math.h>
>
> double sin(double)
> {
> return 1;
> }
>
> int main()
> {
> sin(1);
> return 1;
> }
>
> Why I don't get any warnings like:
>
> sin prevously defined in math.h ...
>
> when I compile with -Wall -pedantic -ansi.
Are you sure? It fails to compile here:
$ cc -std=c89 -pedantic sin.c
sin.c: In function `sin':
sin.c:3: error: parameter name omitted
$ cc -std=c99 -pedantic sin.c
sin.c: In function `sin':
sin.c:3: error: parameter name omitted
> Why is it possible to overwrite the definition of sin, is this part of
> the standard?
There is no definition of sin() at that point. Only a declaration
(i.e. a prototype of the function). Your definition happens to match
the visible prototype, so it accepts your custom definition of sin().
> Secondly the definition (not declaration) of double sin(double) misses
> a variable! Is this ok, when the variable is not referenced in the
> code?
This is not ok, as far as I can tell from the warnings above.
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