error C2248: cannot access protected member declared in class

Question

class TClass
{
    class EmbeddClass
    {
        public:
        ....

        protected:
            virtual ~EmbeddClass() {}

    }   

    boost::scoped_ptr<EmbeddClass> scpEmbeddClass;
}

The vs2010 complains the above code. I can fix the problem by defining the ~EmbeddClass as a public function.

Question> what is the cause of this problem? is it because the destructor of scoped_ptr cannot access the protected ~EmbeddClass ? It seems to me that shared_ptr has no such an issue.

Thank you

Answer 1

Question> what is the cause of this problem? is it because the destructor of scoped_ptr cannot access the protected ~EmbeddClass ?

Yes, that is exactly the issue.

It seems to me that shared_ptr has no such an issue.

I can only assume that you are not storing EmbeddClass objects, but rather objects of a type derived from it in the shared_ptr . In that case, the constructor of the shared pointer will create a deleter that will call the destructor of the most derived type (as seen by the shared_ptr constructor/ reset() /..). Because the most derived type is destroyed by the shared_ptr even if the type mentions the base, it won't call the base destructor.

Answer 2

is it because the destructor of scoped_ptr cannot access the protected ~EmbeddClass ?

Yes.

It seems to me that shared_ptr has no such an issue.

Note that you can have multiple shared_ptr owning a resource, if you do not initialize it or the use count is more than 1, it will never need to call the deleter. However, scoped_ptr is more like unique_ptr , it has unique ownership over the resource and makes sure that it can delete the pointer even if you do not initialize it.

Basically, a shared_ptr that does not own a resource does not require access to the protected destructor while scoped_ptr and unique_ptr do require access.