From: Jeff Flinn (TriumphSprint2000_at_[hidden])
Date: 2007-06-11 17:58:49
Pete Bartlett wrote:
> I have taken over some code that boils down to
> ///begin code
>
> #include <iostream>
> #include <boost/shared_ptr.hpp>
>
> struct base {
> int i;
> base(int i_):i(i_) {}>
> };
>
> struct derived : base
> {
> derived(int i): base(i) {}
> };
>
> int main()
> {
> boost::shared_ptr<derived> pd(new derived(5));
>
> void* ptr_to_pd = &pd;
>
> boost::shared_ptr<base>* ptr_to_pb
> = static_cast< boost::shared_ptr<base>* >(ptr_to_pd);
Why not:
boost::shared_ptr<base> pb = static_pointer_cast<base>(pd);
> std::cout << "\n" << pb->i ; //Prints 5
>
> }
> ///End code
>
> Now shared_ptr<B> and shared_ptr<A> are unrelated types, so IIUC there
> is no guarantee that this will work. Is that right? I know from the
> shared_ptr documentation that I should refactor in the direction of
> dynamic_ptr_cast (though complications not shown in the code above make
> that harder that). However for the time being this code appears to be
> working. Is that just a fluke? I.e. I am relying on the author of
> boost::shared_ptr and/or my compiler creators not to do something such
> that it doesn’t work. Is there the possibility that any memory could be
> deleted twice? Or I am worrying over nothing and in fact there is a
> reason why the above is safe?
See http://www.boost.org/libs/smart_ptr/shared_ptr.htm#functions.
Jeff