On Mon, Mar 19, 2007 at 07:12:24PM -0300, Gustavo Rios wrote:
> I am writing a very simple program but the output change for the c
> variable value change every time i run it. What would it be my mistake
> on the source? Did i forget some thing?
>
> #include <stdio.h>
>
> int
> main(int argc, char **argv)
> {
> unsigned long long x, c;
> unsigned *p;
>
/* stop abusing the comma operator */
> x = 1, x+= (unsigned long long)1 << 33 ;
/* Fine, storing random void * pointers in p is allowd */
> p = (void *)&x;
/*
* You assume that the in memory representation of an
* unsigned [2] looks exactly like unsigned long long and you
* expect to access the valid initialized memory of x by
* dereferencing p.
*
* These assumptions are all wrong.
*/
> c = p[0] * p[1];
>
> fprintf(stdout, "x:%llu\n", x);
> fprintf(stdout, "0,1:%u,%u\n", p[0], p[1]);
> fprintf(stdout, "c:%llu\n", c);
>
> return 0;
> }
>
>
Your program is invalid. Gcc has all rights to fuck it up,
-omg-optimized or not.
Casts are basically syntactic sugar for "(i know what i'm doing, now
shut up and stop complaining)". Remove the (void *) and compile with
-Wall.
Tobias
