On Jan 31, 2012, at 3:53 PM, Alexander Nasonov wrote: > David Laight wrote: >> I don't believe there is a problem using m[0], just m[non-constant-expr]. > > Practically speaking, m[0] is not a problem but the standard says > > ... to the structure member (designated by member-designator), ... > ^^^^^^ > >> OTOH 'sizeof (s *)0->m[0]' might be deemed invalid (because it has >> an inferred dereference of NULL. > > Oh yes. I can change it to: > > extern void *foo(void); > > and then sizeof(((s *)foo())->m[0]) but NULL should work too. > > So, if we reached a consensus on this, where should I add the macro?
There's no NULL dereference, so it is fine (completely standards conforming). The sizeof operator is a compile time construct that evaluates its argument for its type only, so no dereference is happening, so any value for the pointer is OK. In the absence of a local variable, 0 is just as valid as anything else. Warner
