2009/9/23 Chris Robinson <chris.k...@gmail.com>:
> On Tuesday 22 September 2009 12:32:35 am Mike Kaplinskiy wrote:
>> It actually does not dereference anything.
>
> Does the C standard specify that taking the address of a struct member being
> dereferenced doesn't actually cause a dereference, instead just offsetting?
> Doing foo-> is identical to (*foo)., so dmW->dmFormName is the same as
> &(*dmW).dmFormName, which does technically cause a dereference, followed by
> taking the address of the field.
>
> However, since GCC will remove deadcode and it's simple to see the dereference
> isn't needed, it just optimizes it away. I wouldn't even be surprised if this
> behavior is guaranteed by GCC with no optimizations enabled.. but I'm not so
> sure that it's guaranteed by the C standard. Is it?
Worth trying my sample code on non-GCC compilers then:
#include <stdio.h>
#include <stdlib.h>
struct foo
{
int baz[1];
};
int main()
{
struct foo *bar=NULL;
printf("%p\n",(void*)(NULL));
printf("%p\n",(void*)(bar->baz));
printf("%p\n",(void*)((*bar).baz));
printf("%p\n",(void*)(&(*bar).baz[5]));
printf("%d\n",(sizeof(int[5])));
return 0;
}
Expected output:
(nil)
(nil)
(nil)
0x14
20
Is there a reason why sizeof() magic can't be used instead of FIELD_OFFSET? :)
