Accessibility of Derived-to-Base Conversion
by Barbara E. Moo, Josée Lajoie, Stanley B. Lippman
C++ Primer, Fifth Edition
- Title Page
- Copyright Page
- Dedication Page
- Contents
- New Features in C++11
- Preface
- Chapter 1. Getting Started
- Part I. The Basics
- Contents
- Chapter 2. Variables and Basic Types
- Chapter 3. Strings, Vectors, and Arrays
- Chapter 4. Expressions
- Contents
- 4.1. Fundamentals
- 4.2. Arithmetic Operators
- 4.3. Logical and Relational Operators
- 4.4. Assignment Operators
- 4.5. Increment and Decrement Operators
- 4.6. The Member Access Operators
- 4.7. The Conditional Operator
- 4.8. The Bitwise Operators
- 4.9. The sizeof Operator
- 4.10. Comma Operator
- 4.11. Type Conversions
- 4.12. Operator Precedence Table
- Chapter Summary
- Defined Terms
- Chapter 5. Statements
- Chapter 6. Functions
- Chapter 7. Classes
- Part II. The C++ Library
- Contents
- Chapter 8. The IO Library
- Chapter 9. Sequential Containers
- Chapter 10. Generic Algorithms
- Chapter 11. Associative Containers
- Chapter 12. Dynamic Memory
- Part III. Tools for Class Authors
- Contents
- Chapter 13. Copy Control
- Chapter 14. Overloaded Operations and Conversions
- Contents
- 14.1. Basic Concepts
- 14.2. Input and Output Operators
- 14.3. Arithmetic and Relational Operators
- 14.4. Assignment Operators
- 14.5. Subscript Operator
- 14.6. Increment and Decrement Operators
- 14.7. Member Access Operators
- 14.8. Function-Call Operator
- 14.9. Overloading, Conversions, and Operators
- Chapter Summary
- Defined Terms
- Chapter 15. Object-Oriented Programming
- Contents
- 15.1. OOP: An Overview
- 15.2. Defining Base and Derived Classes
- 15.3. Virtual Functions
- 15.4. Abstract Base Classes
- 15.5. Access Control and Inheritance
- 15.6. Class Scope under Inheritance
- 15.7. Constructors and Copy Control
- 15.8. Containers and Inheritance
- 15.9. Text Queries Revisited
- Chapter Summary
- Defined Terms
- Chapter 16. Templates and Generic Programming
- Part IV. Advanced Topics
- Contents
- Chapter 17. Specialized Library Facilities
- Chapter 18. Tools for Large Programs
- Chapter 19. Specialized Tools and Techniques
- Appendix A. The Library
- Contents
- A.1. Library Names and Headers
- A.2. A Brief Tour of the Algorithms
- A.2.1. Algorithms to Find an Object
- A.2.2. Other Read-Only Algorithms
- A.2.3. Binary Search Algorithms
- A.2.4. Algorithms That Write Container Elements
- A.2.5. Partitioning and Sorting Algorithms
- A.2.6. General Reordering Operations
- A.2.7. Permutation Algorithms
- A.2.8. Set Algorithms for Sorted Sequences
- A.2.9. Minimum and Maximum Values
- A.2.10. Numeric Algorithms
- A.3. Random Numbers
- Index
- Add Pages
Accessibility of Derived-to-Base Conversion
Whether the derived-to-base conversion (§ 15.2.2, p. 597) is accessible depends on which code is trying to use the conversion and may depend on the access specifier used in the derived class’ derivation. Assuming D inherits from B:
• User code may use the derived-to-base conversion only if D inherits publicly from B. User code may not use the conversion if D inherits from B using either protected or private.
• Member functions and friends of D can use the conversion to B regardless of how D inherits from B. The derived-to-base conversion to a direct base class is always accessible to members and friends of a derived class.
• Member functions and friends of classes derived from D may use the derived-to-base conversion if D inherits from B using either public or protected. Such code may not use the conversion if D inherits privately from B.
TipFor any given point in your code, if a public member of the base class would be accessible, then the derived-to-base conversion is also accessible, and not otherwise.
Key Concept: Class Design and protected Members
In the absence of inheritance, we can think of a class as having two different kinds of users: ordinary users and implementors. Ordinary users write code that uses objects of the class type; such code can access only the public (interface) members of the class. Implementors write the code contained in the members and friends of the class. The members and friends of the class can access both the public and private (implementation) sections.
Under inheritance, there is a third kind of user, namely, derived classes. A base class makes protected those parts of its implementation that it is willing to let its derived classes use. The protected members remain inaccessible to ordinary user code; private members remain inaccessible to derived classes and their friends.
Like any other class, a class that is used as a base class makes its interface members public . A class that is used as a base class may divide its implementation into those members that are accessible to derived classes and those that remain accessible only to the base class and its friends. An implementation member should be protected if it provides an operation or data that a derived class will need to use in its own implementation. Otherwise, implementation members should be private.
-
No Comment