The operator dynamic_cast<> comes in two flavors: one uses pointers and the other uses references. Accordingly, dynamic_cast<> returns a pointer or a reference of the desired type when it succeeds. When dynamic_cast<> cannot perform the cast, it returns a NULL pointer, or in case of a reference, it throws a std::bad_cast exception:

 void f(Shape & shape) { // A pointer dynamic_cast example:  Circle * p = dynamic_cast < Circle *> (&shape);  // test whether shape's dynamic type is Circle  if ( p ) { p->fillArea (); }     // successful cast; use the resultant pointer  else {} // shape is of a different type than Circle }

You should always place a reference dynamic_cast<> within a try-block and include a suitable catch-statement:

 void f(Shape & shape) { // A reference dynamic_cast example:  try  {          /* attempt to downcast shape */    Circle& ref = dynamic_cast < Circle &> (shape); // reference version of dynamic_cast<>    ref.fillArea(); //successful cast; use the resultant object  }  catch (std:bad_cast& bc)  { }// shape is not a Circle}