Question

I have the following problem. I am busy coding up an inheritance structure in C++. Briefly, this is what I am attempting to do. Class A is the base class and classes B and C are inherited class. Classes B and C each have different and unique member functions.

Now, using the boost smart pointer library I make a vector of shared pointer of class type A as follows:

class A{
   A();
   virtual print();
}

class B : public A{
   B();
   virtual print();
}

class C{
   C();
   virtual print();
   void uniqueFunc();
}

int main(){

  vector<shared_ptr<A> > myA;
  shared_ptr<B> myB;
  shared_ptr<C> myC;

  myA.push_back(myB);
  myA.push_back(myC);

}

Now I have a method for checking the type of members within the vector. This isn’t the issue. My question is, how do I call uniqueFunc for a member of class type C within the vector. Would I have to downcast? Or do I have to create virtual function. I do however, need uniqueFunc to be unique to class C. I would like to avoid creating copies of members and rather directly change the member in the vector.

Answer 1

You either need to downcast to boost::shared_ptr<C> or create a virtual function in A.

Assuming you want to downcast, you could use Boost’s pointer cast functions:

boost::static_pointer_cast<C>(myA.back())->uniqueFunc();

(or use dynamic_pointer_cast<C> if you need dynamic type checking.)