Using dynamic_cast in a few examples to show how its used. (polymorphic)

dynamic_cast_example.cpp

// g++ dynamic_cast_example.cpp -o dynamic_cast_example.x && dynamic_cast_example.x
#include <iostream>
using namespace std;

class A            { public: virtual string class_string() { return "Class A"; } };
class B : public A { public: virtual string class_string() { return "Class B"; } };
class C : public A { public: virtual string class_string() { return "Class C"; } };
class D : public C { public: virtual string class_string() { return "Class D"; } };

// dynamic_cast returns NULL if the cast is impossible and the type is a pointer
void cast_my_ptr( A* pA, string s ) {
  B* pB = dynamic_cast<B*>(pA);
  C* pC = dynamic_cast<C*>(pA);
  D* pD = dynamic_cast<D*>(pA);

  if (pA) cout << s << ":pA = " << pA->class_string() << endl;
  if (pB) cout << s << ":pB = " << pB->class_string() << endl;
  if (pC) cout << s << ":pC = " << pC->class_string() << endl;
  if (pD) cout << s << ":pD = " << pD->class_string() << endl;
};

void cast_my_ref_a2a( A& rAi, string s ) {
  A& rA = dynamic_cast<A&>(rAi);
  cout << s << ":rA = " << rA.class_string() << endl;
};

void cast_my_ref_a2b( A& rA, string s ) {
  B& rB = dynamic_cast<B&>(rA);
  cout << s << ":rB = " << rB.class_string() << endl;
};

void cast_my_ref_a2c( A& rA, string s ) {
  C& rC = dynamic_cast<C&>(rA);
  cout << s << ":rC = " << rC.class_string() << endl;
};

void cast_my_ref_a2d( A& rA, string s ) {
  D& rD = dynamic_cast<D&>(rA);
  cout << s << ":rD = " << rD.class_string() << endl;
};

// dynamic_cast throws exception if the cast is impossible and the type is a reference
void cast_my_ref( A& rA, string s ) {
  B& rB = dynamic_cast<B&>(rA);
  C& rC = dynamic_cast<C&>(rA);
  D& rD = dynamic_cast<D&>(rA);
};

int main() {
  A aobj;
  B bobj;
  C cobj;
  D dobj;

  A* pAobj = &aobj;
  A* pBobj = &bobj;
  A* pCobj = &cobj;
  A* pDobj = &dobj;

  cast_my_ptr(pAobj,"pAobj");
  cast_my_ptr(pBobj,"pBobj");
  cast_my_ptr(pCobj,"pCobj");
  cast_my_ptr(pDobj,"pDobj");

  A& rAobj = aobj;
  A& rBobj = bobj;
  A& rCobj = cobj;
  A& rDobj = dobj;

  cast_my_ref_a2a(rAobj,"rAobj");
  cast_my_ref_a2b(rBobj,"rBobj");
  cast_my_ref_a2c(rCobj,"rCobj");
  cast_my_ref_a2d(rDobj,"rDobj");
  cast_my_ref(rAobj,"rAobj");
  cast_my_ref(rBobj,"rBobj");
  cast_my_ref(rCobj,"rCobj");
  cast_my_ref(rDobj,"rDobj");

}

// Output:
//    pAobj:pA = Class A
//    pBobj:pA = Class B
//    pBobj:pB = Class B
//    pCobj:pA = Class C
//    pCobj:pC = Class C
//    pDobj:pA = Class D
//    pDobj:pC = Class D
//    pDobj:pD = Class D
//    rAobj:rA = Class A
//    rBobj:rB = Class B
//    rCobj:rC = Class C
//    rDobj:rD = Class D
//    terminate called after throwing an instance of 'std::bad_cast'
//      what():  St8bad_cast
//    Abort