Teach Yourself Borland C++ in 14 Days - portal

Totally Immersed: C++ Classes and Object-Oriented Programming
NEW TERM
NEW TERM
NOTE
Inheritance means taking an existing class and adding functionality by deriving a new
class from it.
The class you start with is called the base class, and the new class you create is called
the derived class.
Let’s take the Airplane class as an example. The civilian and military worlds are quite
different, as you know. In order to represent a military aircraft, I can derive a class from
Airplane and add functionality to it:
class MilitaryPlane : public Airplane {
public:
MilitaryPlane(char* name, int _type);
virtual int GetStatus(char* statusString);
protected:
virtual void TakeOff();
virtual void Land()
virtual void Attack();
virtual void SetMission();
private:
Mission theMission;
};
A MilitaryPlane has everything an Airplane has, plus a few more goodies. Note the first line
of the class definition. The colon after the class name is used to tell the compiler that I am
inheriting from another class. The class name following the colon is the base class from which
I am deriving. The public keyword, when used here, means that I am claiming access to all
the public functions and data members of the base class.
When you derive a class from another class, the new class gets all the
functionality of the base class plus whatever new features you add. You
can add data members and functions to the new class, but you cannot
remove anything from what the base class offers.
You’ll notice that in the private section there is a line that declares a variable of the Mission
class. The Mission class could encapsulate everything that deals with the mission of a military
aircraft: the target, navigation waypoints, ingress and egress altitudes and headings, and so
on. This illustrates the use of a data member that is an instance of another class. In fact, you’ll
see that a lot when programming in C++Builder.
There’s something else here that I haven’t discussed yet. Note the virtual keyword. This
specifies that the function is a virtual function.
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