Sams Teach Yourself C in 21 Days

Working with C++ Classes and Objects 689

BD3

Accessing Classes in Classes ........................................................................

You access a class within a class in the same way you would access a nested structure.

Remember that you are accessing data members. To access the xvalue of the starting

point in a line object called line1, you use

line1.start.x

You access the yvalue of the ending point in the same line object by using the following:

Line1.end.y

Inheriting in C++ ................................................................................................

Although C++ offers the capability to nest classes within other classes, C++ also offers a

more powerful feature. This is the third feature of an object-oriented language: inheri-

tance.

Inheritanceis the capability to create new classes by building upon existing classes.

Consider an example. There are people in the world. Every person in the world can be

characterized by a number of features. Characteristics that describe every person include

• a name


• an age


• the country lived in


• other miscellaneous features
  Now consider an employee at a company. Not every person is an employee at a com-
  pany; however, every employee at a company can be considered a person. An employee
  has all the features of a person listed above, plus additional characteristics such as


• the name of a company where work is performed


• a salary


• other miscellaneous features
  Consider a student. A student is not an employee; however, a student is a person. A stu-
  dent, too, has all the characteristics of a person, plus a few additional characteristics such
  as


• a student ID


• a school


• other miscellaneous features

38 448201x-Bonus3 8/13/02 11:19 AM Page 689