On 08/04/2010 10:15 AM, Massimiliano Cialdi wrote: > Il giorno mer, 04/08/2010 alle 10.06 +0100, Andrew Haley ha scritto: > >>> So why if I write: >>> big_dummy_t *p = (big_dummy_t*)0; >>> uint16_t p = (uint16_t)&(p->singledata); >>> >>> I get NO warning? >> >> Because the first is constant folded, the second isn't. Not that it >> matters, because your program is undefined anyway, since you're >> dereferencing a null pointer. > I never read or write data poined by p. I only use it to calculate > offset of fields inside it. It's still pretty dubious. Why not use offsetof? > I could write: > uint16_t p = (uint16_t)((char *)&(p->singledata) - (char*)0); You could, but that's undefined too: you can only subtract pointers that are part of the same array. But I don't see the point of this anyway. You can easily use arithmetic to calculate the offsets in your external flash memory. Andrew.
