Question

I like to have well defined interface in a few classes, for this I created pure virtual functions in an abstract class that each class needs to implement.
But I’m facing the problem that I can instantiate the classes so I have to create another class that inherit the interface class, and all the other classes needs to inherit from this base class. Here is the code for example:

The interface

class Interface
{
     virtual std::string getName() = 0;
}

class Base : public Interface
{
   virtual std::string getName(return std::string("Base") ;)
}

class A : public Base
{
  std::string getName(return std::string("A") ;)

}

class B : public Base
{
  std::string getName(return std::string("B") ;)

}

All this so i could in code to have the same type for A & B.
Can I just use the Interface class without the Base class?
Something like this:

class A : public Interface
{
  std::string getName(return std::string("A") ;)

}

Answer 1

You cannot instantiate the interface, but what you can do is have a pointer to the interface, pointing to an instance of an implementation:

class Interface { /* pure virtual methods */ };
class A : virtual public Interface { /* implement all pure virtual methods */ };
class B : virtual public Interface { /* implement all pure virtual methods */ };

Interface * i0 = new A();
Interface * i1 = new B();

This is a standard way of using polymorphic classes (although you might want to use smart pointers instead of raw pointers).

Edit: concerning the use of virtual inheritance, see here and here for more information.