"Anthony Williams" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Eric Woodruff writes: > > "Anthony Williams" <[EMAIL PROTECTED]> wrote in > > message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > Thus, given that h.storage is properly aligned, (which is the purpose of > > the > > > other union member), after "new(h.storage) Foo", h.storage contains a Foo > > > object. Thus accessing it through a pointer-to-Foo is legal, as Foo is the > > > dynamic type of the object. > > > > > > > This is precisely my reasoning why reinterpret_cast<> is _not_ > > implementation defined. > > > > It must be the case that it is equal to the situation of having > > > > Foo* -> char */void* -> Foo* if Foo is the dynamic type of the object. > > Nowhere do I see a requirement that supports your deductions. Indeed there are > very few requirements on reinterpret_cast<>, other than the fact that what it > does must be defined by the implementation. For pointers to objects, these > amount to: > > * T1* can be converted to T2* and back again unchanged (unless T2 has stricter > alignment requirements).
Precisely, T1 is Foo in this case as you have already pointed out. This is simply the identity conversion T1 -> T2 -> T1, which is pretty much the only thing reinterpret_cast can do portably. > > * You can convert a pointer to the first member of a POD struct to a pointer > to the struct, and vice-versa. > > * A Null pointer of any type can be cast to a null pointer of any other type. > > Anthony > -- > Anthony Williams > Senior Software Engineer, Beran Instruments Ltd. > Remove NOSPAM when replying, for timely response. > > _______________________________________________ > Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost > _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
