>>> Nathan Sidwell <[EMAIL PROTECTED]> 07.12.05 16:58:11 >>> >Jan Beulich wrote: >> This test contains three invocations of Ref(), but only two of them are >> considered ill. What I'd like to get an explanation for is why the third >> (middle) instance is considered correct. After all, the u member of >> Packed is packed, and hence all the members of Unpacked in that context >> are, too. Namely, even if the object referenced by p is properly >> aligned, p.u isn't and hence p.u.i isn't either. >> >> I'm asking this because for *-*-netware*, which uses packed structures >> by default, this test fails with an error message like the ones expected >> on the other two calls to Ref(). > >Although Unpacked is a pod type, if it contained non-static member functions, >those member functions would expect a this pointer that is correctly aligned.
And that is precisely the reason why I think binding a reference to the whole object or any of its members, when the object itself is a member of a packed object, is illegal, hence requiring a diagnostic (unless, like for both other cases, the default is to pack structures). >We have two options >1) don't pack fields of structure type >2) don't pack fields of non-pod or non-static member function containing structs > >#2 means the alignment of your field can change, depending on whether the >field's type contains a non-static member or not. C++ has no term for such a class. > >#1) breaks GNU C compatibility, I think. > >I'm not sure what the best answer is here. > >If your system packs structs by default, you should not be getting the warning >on any of the uses. But I do, and if I use a native Linux compiler with -fpack-struct, I also get it (along with a second one on one of the two other instances). Jan
