Frama-C-discuss mailing list archives

This page gathers the archives of the old Frama-C-discuss archives, that was hosted by Inria's gforge before its demise at the end of 2020. To search for mails newer than September 2020, please visit the page of the new mailing list on Renater.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Frama-c-discuss] Problem with \old

Hello,

two remarks:

1.) ++ has  a higher precedence than * (dereference): http://www.difranco.net/cop2220/op-prec.htm
Therefore, I think your implementation must be written as

void fun(int* p) {
     (*p)++;
}

2.) Even then you must take into account that an overflow can occur when calling ++,
e.g. calling fun with p pointing to INT_MAX.

Regards

Jens

On 20.05.2010, at 12:12, Michael Schausten wrote:

> Hello,
> 
> I'm getting started using Frama-c, but now I'm stuck with a (probably simple) problem.
> My code:
> 
> /*@ ensures (\old(*p) < *p);
> */
> void fun(int* p) {
>  *p++;
> }
> 
> I try to prove it with Alt-Ergo via the GWhy-Tool with
> frama-c -jessie-analysis -jessie-gui fun.c
> 
> It seems to me, that the prover does not make the right usage of \old. In the right part of the gWhy-Tool, it says it tries to prove:
> integer_of_int32(select(int_P_int_M_p_0_22, p_0)) < integer_of_int32(select(int_P_int_M_p_0_22, p_0))
> So apparently, it doesn't try to prove \old(*p) < *p, but rather *p < *p (which is not provable, of course).
> 
> I just can't find out what I'm doing wrong, and I hope you can give me a hint what's the problem with my code.
> 
> _______________________________________________
> Frama-c-discuss mailing list
> Frama-c-discuss at lists.gforge.inria.fr
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/frama-c-discuss


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.gforge.inria.fr/pipermail/frama-c-discuss/attachments/20100520/d090e614/attachment.htm>