Re: [boost] reinterpret_cast : differents structs or classes with identical structural type

From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2007-09-22 07:14:26

Marco Servetto wrote:
> The question is: C++ grants that
> A a;
> a.a2=8.8;
> assert(reinterpret_cast<B*>(&a)->b2==8.8);
>   
Please note that my reply is based on the final public review document
and thus not authoritative.
Yes, it grants this, according to the rules of layout-compatible PODs.
> it is even true for classes with inheritance?
>   
No. The layout-compatibility rules only apply to PODs. POD-structs are
defined by their lack of member pointer members, reference members,
object members of non-POD type (recursively), user-defined copy
assignment and user-defined destructor.
But there is one more requirement: they must be aggregate classes.
Aggregate classes are defined in 8.5.1:

"An aggregate is an array or a class with no user-declared constructors,
no private or protected non-static data members, no base classes, and no
virtual functions."

Sebastian Redl