Re: Casting to a derived class

The proper way to do downcasting is to turn on RTTI and use
dynamic_cast<>(). dynamic_cast<>() verifies that the actual runtime
object really is of the specified class. If called with a pointer
specification, it will return a new, class specific, pointer to the
object if successful or NULL if the object is not of the specified
type.

The way you use dynamic_cast<>() for safe pointer downcasting is
something like the following:

void main(int argc, char *argv[])
{
   base *pb = new der();
   der *pd = dynamic_cast<der*>(pb);

   if ( pd )
      pd->d = 123;
   else
      // pd == null. cast failed - object not a 'der'
      :

}