Re: Casting from void*

From:

Noah Roberts <dont@email.me>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 28 Jun 2011 17:13:27 CST

Message-ID:

<4e0a0b44$0$2391$cc2e38e6@news.uslec.net>

On 6/25/2011 12:47 AM, Joshua Maurice wrote:

I did make the claim that "reinterpret_cast and static_cast between
them are equivalent." To be clear, the claim made was: for all types A
and B, for pointer b of type B*, the following two expressions are
equivalent:
static_cast<A*>(static_cast<void*>(b));
reinterpret_cast<A*>(b);

Are you sure about this?

Correct me if I'm wrong:

A static cast to void* is guaranteed to create a pointer that points at
the beginning of the object. Thus:

struct X { ... };
struct Y { ... };
struct Z : X,Y { ... };

Y * ptr = new Z;

void * vptr = ptr;

Now ptr != vptr. Instead vptr == static_cast<X*>(ptr).

Then static_cast<A*>(vptr) can do the same sort of thing but in reverse
and on an unrelated tree of objects.

On the other hand, reinterpret_cast<A*>(ptr) == ptr no matter what the
inheritance looks like for either types.

Any of that in error?

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