[Swan-dev] pointer initialization and fcfcde7422a4805a56a3a4a175271c56fbbbab12

[Lennart Sorensen]

On Mon, Jul 04, 2016 at 03:15:17PM -0400, D. Hugh Redelmeier wrote:
> Let me be clearer.  A pointer value that is null must test equal to
> zero.  Not true of the raw bytes of a null pointer (no conversion
> happens when you deal with the raw bytes of a pointer).
> 
> void *p;
> ...
> 	passert(NULL = 0);	/* must not fail */
> ...
> 	memset(&p, 0, sizeof(p));
> 	passert(p == 0);	/* may fail */
> ...
> 	p = 0;
> 	passert(p == 0);	/* must not fail */
> ...
> 	static const unsigned char zeros[sizeof(void *)];
> 	p = 0;
> 	passert(memcmp(&p, zeros, sizeof(void*)) == 0); /* may fail */
> 
> Some machines with segmented memory take advantage of this liberty.
> But most of those have died out.

So did their compiler explicitly handle a cast of a 0 value integer to
a pointer and map it to the "correct" null pointer address value?

That seems horribly complicated to manage.

-- 
Len Sorensen