Wrox Press C++ Tutorial

Summary

In this chapter, we've covered all of the principal ideas involved in using inheritance. The fundamentals that you should keep in mind are these:

• A derived class inherits all the members of a base class except for constructors, the destructor and the overloaded assignment operator.
  
  
• Members of a base class which are declared as private in the base class are not accessible in any derived class. To obtain the effect of the keyword private but allow access in a derived class, you should use the keyword protected in place of private.
  
  
• A base class can be specified for a derived class with the keyword public, private, or protected. If none is specified, the default is private. Depending on the keyword specified for a base, the access level of the inherited members may be modified.
  
  
• If you write a derived class constructor, you must arrange for data members of the base class to be initialized properly, as well as those of the derived class.
  
  
• A function in a base class may be declared as virtual. This allows other definitions of the function appearing in derived classes to be selected at execution time, depending on the type of object for which the function call is made.
  
  
• You should declare the destructor in a base class containing a virtual function as virtual. This will ensure correct selection of a destructor for dynamically created derived class objects.
  
  
• A class may be designated as a friend of another class. In this case, all the function members of the friend class may access all the members of the other class. If class A is a friend of B, class B is not a friend of A unless it has been declared as such.
  
  
• A virtual function in a base class can be specified as pure by placing =0 at the end of the function declaration. The class will then be an abstract class for which no objects can be created. In any derived class, all the pure virtual functions must be defined; if not, it too becomes an abstract class.
  
  
• A class may be derived from multiple base classes, in which case it inherits members from all of its bases, with the exception of destructors, constructors and overloaded assignment operator functions.
  
  
• An indirect base class should be specified as virtual for derived classes when using multiple inheritance, in order to avoid duplicate occurrences of its data members in a class with multiple bases, two or more of which are derived from the indirect base.

We have now gone through all of the important language features of C++, and by now you should be comfortable with most of them. You can go back and play with the source code to try out your new skills - you could try to extend the existing examples we've been through. Remember that the code for all of the examples is available for download form the Wrox Press website: http://www.wrox.com.