reference to abstract class

Question

What does it mean when there is a reference to an abstract class? I found it in code and I can\'t understant it.

I thought that an abstract class can\'t be instantia

Answer 1

class Abstract
{
public:
  virtual void foo() = 0;
};

class Implementation : public Abstract
{
public:
  void foo() { std::cout << "Foo!" << std::endl; }
};

void call_foo(Abstract& obj) { obj.foo(); } 

int main()
{
  Abstract *bar = new Implementation();

  call_foo(*bar);

  delete bar;
}

bar is a pointer to an abstract class. It can be dereferenced using the * operator and passed as a reference into call_foo, because that is what call_foo is asking for (Abstract* would be asking for a pointer, whereas Abstract& is asking for a reference).

In the above, the reference to the abstract class is passed, and when foo() is called using the . notation (instead of the pointer -> notation), it prints Foo!, because that is what the Implementation does.

Hope this helps.