Additional Software Engineering Issues

Now that class GradeBook is defined in a header, the class is reusable. Unfortunately, placing a class definition in a header as in Fig. 3.9 still reveals the entire implementation of the class to the class’s clients—GradeBook.h is simply a text file that anyone can open and read. Conventional software engineering wisdom says that to use an object of a class, the client code needs to know only what member functions to call, what arguments to provide to each member function and what return type to expect from each member function. The client code does not need to know how those functions are implemented.

If client code does know how a class is implemented, the programmer might write client code based on the class’s implementation details. Ideally, if that implementation changes, the class’s clients should not have to change. Hiding the class’s implementation details makes it easier to change the class’s implementation while minimizing, and hopefully eliminating, changes to client code.

In Section 3.7, we show how to break up the GradeBook class into two files so that

1. the class is reusable,

2. the clients of the class know what member functions the class provides, how to call them and what return types to expect, and

3. the clients do not know how the class’s member functions are implemented.