Re: low-level question

Keith Thompson wrote:
> "Robert Gamble" <rgamble99@xxxxxxxxx> writes:
> > jesso wrote:
> >> I couldn't get this on a midterm. Darn!
> >>
> >> Anyone want to help?
> >>
> >> 1. Why does the following program output a 0?
> >> 2. Explain in detail.
> >> 3. How could you prevent this outcome without changing the code?
> >>
> >>
> >> #include <stdio.h>
> >> #include <string.h>
> >>
> >> int
> >> main( int argc, char *argv[] )
> >> {
> >> int ii = 1;
> >> char buf[ 4 ];
> >>
> >> strcpy( buf, "AAAA" );
> >>
> >> printf( "%d\n", ii );
> >>
> >> return 0;
> >> }
> >
> > It is undefined behavior in C because you are writing past the end of
> > an arry ("AAAA" is 5 characters, buf is 4). Since it is undefined
> > behavior, anything can happen. There might be certain behaviors that
> > are more likely to occur than others due to nuances of your specific
> > platform but I can't think of anything plausible that would account for
> > the behavior suggested by the question.
>
> If ii is allocated just after the end of buf, and if the platform uses
> a little-endian representation for int, the '\0' of "AAAA" could
> plausibly be written over the low-order byte of ii, causing it to be
> set to 0.

Yep, I was being a little bit narrow-minded when I posted that. I
realized this shortly after I posted and then saw that Lew Pitcher
covered this case so I didn't feel the need to amend my post.

Robert Gamble

.

Relevant Pages

  • Re: low-level question
    ... jesso wrote ... Darn! ... Why does the following program output a 0? ... If you got this question 'wrong' on your midterm, ...
    (comp.lang.c)
  • Re: low-level question
    ... Darn! ... Why does the following program output a 0? ... If ii is allocated just after the end of buf, and if the platform uses ... a little-endian representation for int, ...
    (comp.lang.c)