Re: Q: void* vs. unsigned long
H. Peter Anvin (hpa@transmeta.com)
Mon, 15 Feb 1999 21:43:39 -0800 (PST)
> On 16 Feb 1999, H. Peter Anvin wrote:
>
> > > sizeof (void *) == sizeof (unsigned long) if and only if you are on a
> > > 32-bit arch, like i386.
> >
> > Actually, it will. sizeof(unsigned long) == sizeof(void *) == 8 on
> > 64-bit architectures.
>
> And probably a couple 16-bit systems as well. But that's just
> coincidence. For instance, if the 386 wasn't so woefully register-impaired,
> unsigned long would be 64-bit. And I'd bet a quarter that sizeof(void *)
> will not be 16 on a 128-bit machine (when we finally see one).
>
> But what we need here is "an integral type which can represent all
> possible pointer values". Unsigned long should be safe for that on all
> sane architectures/compilers[1] and might even be guaranteed by the C
> standard. Probably won't work on all DSPs though, but we're not likely to
> see any of those running Linux soon for other reasons.
>
I've personally been fond of poi_t (pointer or integer _t):
typedef union {
void *p;
signed long s;
unsigned long u;
} poi_t;
... or the respective. Of course, if one doesn't like unions, one can
do the same thing as a typedef to the integral type.
-hpa
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