Chapter 1, Problem 8E

Program Plan Intro

Class Access Modifiers:

The feature of object oriented programming that allows prevention of program functions to access a class type’s internal representation directly.

There are three access specifiers used in the class to restrict the access of members inside the class. They are as follows:

• Public
• Protected
• Private

For classes and members, the default access specifier is “private”.

Sample code:

/* class Base defines the member functions and variables with appropriate access modifiers */

class Base

{

  public:

  //public members

  protected:

  // protected members

  private:

  // private members

};

Explanation of Solution

Private members:

From outside of a class, a member variable that is private could not be accessed, or viewed. Class could access members that are private and friend functions only.

By default, class members are private, for example in class given below “width” denotes a private member, which denotes that until a label is provided to a member, it would be assumed as a private member:

/* class lBox defines member functions “lsetWidth” and “lgetWidth”*/

class lBox

{

  // Variable declarations

  double lwidth;

  public:

  // Variable declarations

  double length;

  // Member function declarations

  void lsetWidth( double lwid );

  double lgetWidth( void );

};

The data is defined in private members, and related functions are defined in public section, so that it could be called from outside of a class, as shown in below program.

This program shows the usage of “Private” access modifier, in which member variables could not be accessed from outside of class.

// Select header files

#include <iostream>

using namespace std;

Declare the class lBox that defines the member functions “lsetWidth()” and “lgetWidth()” to set  and return the width for box.

//Create the class

class lBox

{

  public:

  // Variable declarations

  double length;

  // Member function declarations

  void lsetWidth( double lwid );

  double lgetWidth( void );

  private:

  // Variable declarations

  double lwidth;

};

Define the member function lgetWidth() to return width of box...

Explanation of Solution

Protected members:

A protected member function or variable denotes similarity to a private member. That is, from outside of a class, accessing a member variable or function that is protected is not possible.

• An additional benefit is that they can be accessed within child classes which are known as derived classes.
• In below example, “width” member could be accessed by the derived class “SmallBox” member function.

This program shows the usage of “Protected” access modifier, in which member variables could not be accessed from outside of a class, but it could be accessed within child classes which are termed as derived classes.

// Select header files

#include <iostream>

using namespace std;

Declare the class lBox that defines the variable “width” to set  and return the width for box.

// class lBox defines “width” as a protected variable”

class lBox

{

  protected:

  // Variable declarations

  double width;

};

Declare the class “SmallBox” that defines the member functions “lsetSmallWidth()” and “lgetSmallWidth()” to set and return the width for box...