Re: dynamic cast

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 25 Sep 2007 17:58:39 CST

Message-ID:

<9WfKi.124374$U01.992380@twister1.libero.it>

Sarang ha scritto:

Hi,

I work on a large legacy system where in we have our own RTTI Module.
Most of the system has been written in C.

RTTI Module is used extensively for downcasting and type
identification, that what it's meant to do.

e.g.,
class BaseObject : public Object
class SomeObject : public BaseObject

//BaseObjectType represents BaseObject

Object* ptr = something;
if( RTTI_is_subclass(ptr->GetClassType(),BaseObjectType) )
{
BaseObject* basePtr = (BaseObject*)ptr;
}

Now the question is what are the benefits of using dynamic_cast here
instead of C-style cast, which can be re-interpret cast or static cast
depending upon the compiler knowledge about the conversion between the
types?

First of all, you should never want to use reinterpret_cast in this
case, because it might not properly handle multiple or virtual
inheritance. You definitely should prefer static_cast over C-style casts
to have the guarantee that reinterpret_cast is never performed.

Second, dynamic_cast is able to perform a cross-cast, something that no
other cast is able to do correctly. However, as you only check for
subclasses I assume your RTTI module is not able to detect such possibility.

dynamic_cast is also able to provide checking, but you are already using
your RTTI module to perform such checking, so that may not qualify as an
"advantage" in your specific case.

Ganesh

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