Bruce Eckel's Thinking in C++, 2nd Ed Contents | Prev | Next

Multiple inheritance

Of course, the RTTI mechanisms must work properly with all the complexities of multiple inheritance, including virtual base classes: 

//: C24:RTTIandMultipleInheritance.cpp
#include <iostream>
#include <typeinfo>
using namespace std;

class BB {
public:
  virtual void f() {}
  virtual ~BB() {}
};
class B1 : virtual public BB {};
class B2 : virtual public BB {};
class MI : public B1, public B2 {};

int main() {
  BB* bbp = new MI; // Upcast
  // Proper name detection:
  cout << typeid(*bbp).name() << endl;
  // Dynamic_cast works properly:
  MI* mip = dynamic_cast<MI*>(bbp);
  // Can't force old-style cast:
  //! MI* mip2 = (MI*)bbp; // Compile error
} ///:~

typeid( ) properly detects the name of the actual object, even through the virtual base class pointer. The dynamic_cast also works correctly. But the compiler won’t even allow you to try to force a cast the old way:

MI* mip = (MI*)bbp; // Compile-time error

It knows this is never the right thing to do, so it requires that you use a dynamic_cast.

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