C++ programming public, private inheritance
- 1. Object Oriented Programming (CS1143) Department of Computer Science Capital University of Science and Technology (CUST) Week 7
- 2. Outline Single Public, Private, Protected Inheritance Constructor and Destructor Chaining 2
- 3. Inheritance Inheritance enables you to define a general class (i.e., a base class) and later extend it to more specialized classes (i.e., derived classes). For example we can give the definition of an animal; we can then add to the definition to create the definition of a horse. There is an is-a relation from the more specific to the more general. All horses are animals. 3
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- 5. Base Class and Derived Class In C++, the most general class is called the base class (or super class) and a more specific class is called the derived class (or subclass). The derived class inherits all of the data members and member functions of the base class (with the exception of constructors and destructors), and it can create new data members and member functions. 5
- 6. Private, Public and Protected Inheritance To create a derived class from a base class, we have three choices in C++: private inheritance, protected inheritance, and public inheritance. To show the type of the inheritance we want to use, we insert a colon after the class, followed by one of the keywords (private protected, or public) The most common is the public inheritance. In the figure below, B is the base class and D is the derived class. 6
- 7. Public Inheritance The most common type of inheritance is public inheritance. The other two types of inheritance are rarely used. Some other object-oriented languages, like Java, have only public inheritance We will discuss it using an example 7
- 8. Example 8
- 9. Example We design two classes, Person and Student The class Student inherits from the class Person. Person class uses only one data member: identity. Student class needs two data members: identity and gpa. However, since the identity data member is already defined in the class Person, it does not need to be defined in the class Student because of inheritance. Similarly the Student class does not need to define its own set and get functions for identity. 9
- 10. 10 Person Class
- 11. 11 Student Class
- 12. main 12
- 13. 13 Output
- 14. Description On line 54, an object of the student class calls the member function of its base class (Person) as if it were its own function 14
- 15. Private Members in Public Inheritance A private data member in the base class is inherited in the derived class, but it becomes inaccessible in the derived class; it must be accessed only through its own class member functions. 15
- 16. Public and Protected Members in Public Inheritance A public member in the base class becomes a public member in the derived class. A protected member in the base class becomes a protected member in the derived class. The functions defined in the derived class can easily access a protected member without having to call a function inherited from the base class 16
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- 19. Three Types of Inheritance Although public inheritance is by far the most common type of derivation, C++ allows us to use two other types of derivation: private and protected. 19
- 20. Outline Single Public, Private, Protected Inheritance Constructor and Destructor Chaining 20
- 21. Constructors and Destructors Unlike data fields and functions, the constructors and the destructor of a base class are not inherited in the derived class. The constructors and the destructor are not inherited because an object of a derived class naturally has more data members than a corresponding base class. The constructor of a derived class must construct more; the destructor of a derived class must destruct more. 21
- 22. Calling Base Class’s Constructors You can invoke the base class’s constructor from the constructor initializer list of the derived class. If a base constructor is not invoked explicitly, the base class’s no- argument constructor (default constructor) is invoked by default. 22
- 23. Constructor Chaining When constructing an object of a derived class, the derived class constructor first invokes its base class constructor before performing its own tasks. This is called constructor chaining. 23
- 24. Destructor Chaining The destructors are automatically invoked in reverse order. When an object of a derived class is destroyed, the derived class destructor is called. After it finishes its tasks, it invokes its base class destructor. This is called destructor chaining. 24
- 25. Example Calling base class constructor implicitly 25
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- 29. Example Calling base class constructor explicitly 29
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