For example:
class Animal
{
virtual void dummy() {}; //LINE1
}
class Cat : public Animal
{
}
Animal* a = new Cat();
if (Cat* c = dynamic_cast<Cat*> (a)) //LINE2
{
//Do something.
}
If I remove LINE1 from the Animal class (i.e. Animal class does not contain virtual members), LINE2 will not work.
dynamic_cast can cast to the same class or base class without virtual members. But for downcasting or casting to void* (which yields a pointer to the most derived class object) dynamic_cast requires a polymorphic class, per C++11 §5.2.7/6:
“Otherwise,
vshall be a pointer to or an lvalue of a polymorphic type”
where v is the argument you supply.
A polymorphic class is one that has one or more virtual member functions, §10.3/1:
“A class that declares or inherits a virtual function is called a polymorphic class.”
Yes it does, as per the standard, dynamic_cast can only downcast polymorphic types (i.e. a type with at least one virtual function)
