Paul Gilmartin wrote:
> > ...
> > Maybe, if you overlay the pointer with an int, assigning zero could work,
> > because zero addresses in pointer variables are not translated and
> > dereferencing such pointer variables could still work?
> >
> Type punning. Most implementations state that the
> effect of type punning is implementation-dependent
> or unpredictable.
>
Type-punning _is_ "badness" for sure!
Newer C standards allow it thru characters (which is an interesting
change... perhaps because a "char" is basically a byte.)
But - Gil is correct - in this case:
union u {
void *p;
int i;
} u;
doing:
u.i = 0;
followed by:
if(u.p == 0) {
is no good and undefined. (This also completely neglects the
idea that pointers and integer might be totally different sizes.)
We can propose a different question that's along similar lines though.
What if we have:
struct s {
void *p;
int i;
} s;
...
memset(&s, 0, sizeof(s));
what is the value of 'p' then? It would be filled with 0 bytes, so
then what would:
if(s.p == 0) {
mean? (See my other post...)
- Dave R. -
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