C++ Programming: Cross Casts

A multiply inherited class object can be converted into a second base class.

For ex:


struct A
{
  int i;
  virtual ~A () {}
};

struct B {  bool b; };

struct D: public A, public B
{
  int k;
  D() { b = true; i = k = 0; }
};

A *ptra = new D;
B *ptrb = dynamic_cast< B* >ptra;

The static type for ptra is A * where as the dynamic type is D *. Normal static cast can't be used here as A and B are two different structures. reinterpret_cast<> will result in simply assigning ptra to ptrb. But the address of B subobject and A subobject in D are different. So to do so we have to calculate the address of B at runtime which can be achieved by dynamic_cast<>

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