Chapter 12: Object-Oriented Programming: Inheritance

1. a ComissionEmployee class which represents an employee who is paid a percentage of gross sales
   • CommissionEmployee.h
   • CommissionEmployee.cpp
   • fig12_06.cpp
     • See P.161 for "fixed" and "setprecision(2)".
2. Creating a BasePlusCommisionEmployee Class Without Using Inheritance
   • BasePlusCommissionEmployee.h
   • BasePlusCommissionEmployee.cpp
     • Note the similarity between this class and class CommissionEmployee
   • fig12_09.cpp
3. Creating a BasePlusCommissionEmployee Class Inherited from CommissionEmployee
   • BasePlusCommissionEmployee.h
     • This file is shorter (only 26 lines). Compare with the above one (Fig12.7), which has 45 lines.
   • BasePlusCommissionEmployee.cpp
     • In earnings(), it tries to access commissionRate and grossSales, which are private members of the base class. This will cause a compilation error 'commissionRate is private'.
   • main program
     • Compile this derived class with the base class CommissionEmployee (CommissionEmployee.h , CommissionEmployee.cpp)
4. ComissionEmployee-BasePlusCommissionEmployee Inheritance Hierarchy Using protected Data
   • the same main program
   • The same derived class BasePlusCommissionEmployee (BasePlusCommissionEmployee.h , BasePlusCommissionEmployee.cpp)
   • Data members of the base class are declared as protected. You only need to rewrite the class definition CommissionEmployee.h. The implementation CommissionEmployee.cpp need not be changed.
   • Now compile again. You will see the derived class can access those protected data members.
5. However, the author suggests , from Software Engineering Observation, to declare private data and access them via the class's set and get member functions.
   • BasePlusCommissionEmployee.h is the same as the above.
   • BasePlusCommissionEmployee.cpp accesses the private data members of the base class via set and get member functions.
     • On P.557 L.35, when the derived class needs to invoke a based-class member function (which has been redefined in the derived class), the syntax is to place the base-class name and the scope resoltuion operator (::) before the base-class member-function name.
   • CommissionEmployee.h is the same as 1.
   • In CommissionEmployee.cpp, earnings() and print() also access its own private data members via those get and set member functions, although this is not necessary.
   • the same main program as the above one.
6. 12.5 Constructors and Destrucotrs in Derived Classes