From: Terje Slettebø (tslettebo_at_[hidden])
Date: 2002-12-10 08:18:04
>From: "Johan Nilsson" <johan.nilsson_at_[hidden]>
> The hack makes no 'fixed' assumptions on binary object
> layout, rather, it relies on the fact that any polymorphic type can be
> queried for an implemented interface (aka 'base class'). It does, however,
> make the assumption that the location of the rtti itself data is fixed for
a
> specific c++ implementation across different polymorphic types.
>
> Sample usage (demonstrating syntax only):
> --------------
>
> void foo(void*)
> {
> try
> {
> IMyBaseClass* pmc = dynamic_void_cast<IMyClass>(pv);
>
> if (pmc)
> {
> pmc-MyFn();
> }
> }
> catch (std::exception&)
> {}
> }
>
>
> The hack:
> ------
> template<typename T>
> T* dynamic_void_cast(void* pv)
> {
> struct rtti_obj__
> {
> virtual ~rtti_obj__() = 0;
> };
>
> rtti_obj__* pro = static_cast<rtti_obj__*>(pv);
>
> try
> {
> return dynamic_cast<T*>(pro);
> }
> catch (bad_cast&)
> {
> throw;
> }
> catch (exception& e)
> {
> throw bad_cast(e.what());
> }
> }
>
> ----------
Why do you catch, and just rethrow exceptions? Why not just let them
propagate (no try/catch), or turning them into return zero? Also, what other
exception, besides bad_cast, can dynamic_cast throw, which necessitates the
second catch clause?
Regards,
Terje