Inheritance

Public Inheritance

class Super { };
class Sub : public Super { };

Members in base class	Members in subclass
public	public
protected	protected
private	private

Subtyping: a Sub* can be cast to Super* and vice versa.

Protected Inheritance

class Super { };
class Sub : protected Super { };

Members in base class	Members in subclass
public	protected
protected	protected
private	private

Subtyping: a Sub* can be cast to Super* and vice versa, only within the hierarchy.

Private Inheritance

class Super { };
class Sub : Super { };

Members in base class	Members in subclass
public	private
protected	private
private	private

Subtyping: a Sub* can only be cast to Super* and vice versa inside Sub. To the outside world, Super and Sub appear unrelated.

Virtual

class Shape
{
public:
    virtual ~Shape() { }    // Virtual destructor
    virtual void foo();     // Overridable, must have body defined somewhere
    virtual void bar() = 0; // Abstract method
};

While not strictly necessary anymore thanks to smart pointers, it might be safer to still define a virtual destructor in a class hierarchy’s superclass, empty if need be.

Interfaces

An interface in C++ is nothing more than a class with nothing but pure virtual member functions.

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