Date: Thu, 02 Dec 2004 10:51:29 +0100 From: Andrea Venturoli <ml.diespammer@netfence.it> To: Rob <spamrefuse@yahoo.com> Cc: FreeBSD <freebsd-questions@freebsd.org> Subject: Re: gcc violates const-ness of variable? Message-ID: <41AEE5A1.2030405@netfence.it> In-Reply-To: <41AEC075.50207@yahoo.com> References: <41AEC075.50207@yahoo.com>
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Rob wrote:
> Hi,
>
> This should probably be discussed in the GNU gcc mailinglist.
> But I'm more familiar here, and I first want to share it here
> with other FreeBSD users.
>
> I'm surprised about this piece of code:
>
> #include<stdio.h>
> int main()
> {
> const int n = 0;
> scanf("%d", &n);
> printf("%d\n", n);
> return 0;
> }
>
> With gcc compiler, the constant variable 'n' will be overwritten
> by the scanf statement. With g++ it (silently) is not.
> So, I get following:
>
> $ gcc -W -Wall code.c
> code.c: In function `main':
> code.c:5: warning: writing into constant object (arg 2)
> $ ./a.out
> 9
> 9
> $ g++ -W -Wall code.c
> code.c: In function `int main()':
> code.c:5: warning: writing into constant object (arg 2)
> $ ./a.out
> 9
> 0
>
> Is this a bug in gcc, or a feature?
Well, I do not know the precise answer, I'd have to look in the
standards and have no time right now, so I'll just give you some pointers...
gcc -W -Wall code.c -> C compiler/you are compiling C code
g++ -W -Wall code.c -> C++ compiler/you are compiling C++ code
The source seems a mix of *standard* C and C++: stdio.h does not exist
in C++, it might only be there for legacy code, but it works most of the
times; IIRC "const" does not exist in *standardized* C...
gcc should ignore that (I guess), unless you specify -traditional.
"const" exists in C9X, which is not yet an official standard. I think
gcc will support that, possibly with some command line switch or
#define; I'm sure on Debian GNU/Linux some of the library features are
turned on the latter way.
bye
av.
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