On 3/19/07, Gustavo Rios <[EMAIL PROTECTED]> 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;
^ this is bad. always say your types in full.
x = 1, x+= (unsigned long long)1 << 33 ;
This sets *(&x) to 1, and then sets *(&x) (yes, the same one) to 1+(1<<33)
p = (void *)&x;
c = p[0] * p[1];
That is, p[1] == *(&x+1) is never getting set to anything. Thus the
reason the output is always changing is because p[1] is always
pointing at a different, random location in memory that has some
previous value.
Further, p[1] is not your memory, and it's only by chance that you're
not segfaulting.
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;
}
-Nick
