1. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 1 - C++ Inheritance Data Abstraction and Abstract Data Types Abstract Data Type Encapsulated data type Accessible only through interface Properties Defined by the interface not by the Internal structure or Implementation Data Abstraction Effective technique for extending predefined type system When one has a single clearly defined concept

2. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 2 - C++ Inheritance Inheritance In C++ Inheritance is a mechanism for Building class types from other class types Defining new class types to be a …. Specialization Augmentation of existing types

3. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 3 - C++ Inheritance Inheritance Inheritance is a familiar concept…. Inherit From parents In Biology Kingdom Phylum Class Order Family Genus Species Vehicles Land Based Auto Bicycle

4. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 4 - C++ Inheritance Inheritance Subgroupings with respect to a parent are called  Subclass  Derived Class  Children The subclass Inherits  Characteristics  Properties  Capabilities The subclass can modify or extend inherited abilities

5. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 5 - C++ Inheritance Inheritance Vehicle Class Land Based BicyclesAutos myVehicle myLandBased myAuto myBicycle Instance

6. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 6 - C++ Inheritance Inheritance Instance hierarchy follows the class hierarchy Single Inheritance Each object has a single parent Class Instance Multiple Inheritance Classes inherit from multiple base classes Defines a relationship Between several (independent) class types

7. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 7 - C++ Inheritance Multiple Inheritance Vehicle Land Based Automobile Motor Boat AutoBoat Water Based Multiple Parents Common Ancestor

8. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 8 - C++ Inheritance Multiple Inheritance Can also have inheritance without common parent…. Motor Boat Inherits from 2 independent classes  Vehicle  Taxable Item Vehicle Water Based Luxury Item MotorBoat Taxable Item

9. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 9 - C++ Inheritance Virtual Inheritance The derived class AutoBoat…… Inherits Attributes and Properties From Automobile Motor Boat Vehicle Land Based Automobile Motor Boat AutoBoat Water Based

10. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 10 - C++ Inheritance Inheritance - Derivation Hierarchy The class vehicle is an abstraction….. It represents an encapsulation of common Properties Attributes Its sole purpose Define a class from which to derive other classes…... It encapsulates common Data members Function members Called Abstract base class Abstract super class

11. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 11 - C++ Inheritance Inheritance - Abstract Super Class  Key element in the derivation hierarchy  Ensures that all derived classes Share a common set of class members inherited from abstract super class  Provides a common public interface to the class hierarchy

12. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 12 - C++ Inheritance C++ Class Derivation Any class can serve as a base class... Thus a derived class can also be a base class. Worth spending time at the outset of a design to develop sound definition. syntax class DerivedClassName : specification BaseClassName DerivedClassName - the class being derived specification - specifies access to the base class members public protected private - private by default

13. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 13 - C++ Inheritance C++ Class Derivation class A be derived from base class B or C B public C private 1.class A : public B 2.class A : private C

14. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 14 - C++ Inheritance C++ Class Derivation class A : public B In class A The inherited public members of B Appear as public members of A If myValue is a public data member of B myValue can be accessed publicly through instances of A A d; d.myValue;// ok

15. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 15 - C++ Inheritance C++ Class Derivation class A : private B In class A The inherited public members of B Appear as private members of A if myValue is a public data member of B myValue cannot be accessed publicly and directly through instances of A A d; d.myValue;// compile error Function members of A can still access public members of B as public

16. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 16 - C++ Inheritance C++ Class Derivation - Public Derivation class A { } class C : public B { } Objects are created from the inside out and... A Part B Part C Part C Object B Part C Part Constructors A :: A B :: B C :: C

17. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 17 - C++ Inheritance C++ Class Derivation - Public Derivation class A { } class C : public B { } Objects are destructed from the outside in: C Part B Part A Part C Object B Part A Part Destructors C :: C B :: B A :: A

18. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 18 - C++ Inheritance C++ Class Derivation - Constructors and Destructors Constructors and destructors are not inherited…. Initialization and Deinitialization Implemented as series of constructor calls Base Derived classes Different constructors and destructors collaborate to complete the tasks

19. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 19 - C++ Inheritance C++ Class Derivation - Constructors and Destructors When derived object instantiated, memory allocated for Base object Added parts Initialization then occurs in two stages…... Base class constructors invoked to initialize the base objects Derived class constructor invoked to complete the task Derived class constructor Specifies base class constructor in the initialization list If no constructor in the base class use the default If the base class is derived the procedure applied recursively

20. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 20 - C++ Inheritance C++ Class Derivation - Constructors and Destructors Inherited Member Initialization If the base class has only a default constructor Initialize the member values in body of the derived class constructor If the base class has constructor with arguments The initialization list is used to pass arguments to the base class constructors syntax DerivedClass ( derivedClass args ) : BaseClass ( baseClass args ) { DerivedClass constructor body }

21. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 21 - C++ Inheritance C++ Class Derivation - Member Access Under Derivation C1 Defines the base class members C2 Over rides c ( ) Defines e ( ) C3 Over rides d ( ) If C3 accesses aselfc2 c1 bselfc2 c1 cselfc2 dself eself c2 C1 C1 C2 C2 C3 C3 data member a function member b() function member c() function member d() function member c() function member e() function member d()

22. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 22 - C++ Inheritance C++ Class Derivation - Member Access Under Derivation 1.Access to inherited members by derived members and friends FIs independent of the base class designation in the derivation specification FAccess is allowed to all non-private inherited members FAccess is not allowed to private members (of the parent)

23. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 23 - C++ Inheritance C++ Class Derivation - Member Access Under Derivation 2.Access to inherited members by functions outside the derivation hierarchy is driven by the base class designation in the derivation specification. If the specification is public public members remain public protected members remain protected protected inherited non-private members accessible as protected private no outside access

24. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 24 - C++ Inheritance C++ Class Derivation - Member Access Under Derivation 3.Over riding - An inherited member that is normally visible can be masked Define a derived class member with the same name This is not good practice with non-virtual functions.

25. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 25 - C++ Inheritance C++ Class Derivation Derivation Guidelines 1. Derivation is not always the best way to extend the system. 2.Use public derivation When the derived object is a kind of (AKO) base class 3.Use private derivation When the derived object is not a kind of base class but derivation makes code development easier. 4.Use protected derivation When private derivation is suitable but member access from further derived classes is desirable.

26. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 26 - C++ Inheritance C++ Class Derivation Base Class Member Specification Guidelines Classes designed as base classes are the same as ordinary classes Declare as protected Function and data members Intended to be inherited but not intended to be public. Declare as virtual Function members intended to be implemented by derived classes.

27. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 27 - C++ Inheritance C++ Class Derivation - Member Layout Single Inheritance struct A { int a1; void af ( ); }; struct B : A { int b1; void bf1 ( ); }; B :: b1 A*, B* -> A :: a1 A* -> A :: a1

28. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 28 - C++ Inheritance C++ Class Derivation - Member Layout Multiple Inheritance struct C { int c1; void cf ( ); }; struct D : A, C { int d1; void df1 ( ); }; C :: c1 C* -> D :: d1 A*, D* -> C :: c1 C* -> A :: a1

29. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 29 - C++ Inheritance C++ Class Derivation - Member Layout Virtual Inheritance struct E : virtual A { int e1; void ef ( ); }; E :: vbptr E :: e1 E* -> Shared Members

30. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 30 - C++ Inheritance C++ Class Derivation - Private Derivation If the derivation specification is changed to….. class BaseClass { public: BaseClass() {baseValue = 20;} int baseValue; }; class DerivedClass : private BaseClass main (void) { DerivedClass child; child.baseValue = 30;// compile error }

31. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 31 - C++ Inheritance C++ Class Derivation - Private Derivation Exemptions C++ provides a means through which individual members can be made exempt from a private derivation syntax Data members BaseClass :: data member Function members BaseClass :: function member

32. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 32 - C++ Inheritance C++ Class Derivation - Protected Derivation If the derivation specification is changed to Class DerivedClass : protected Base Class  Public and protected members are inherited as protected  Protected members r Act as public within the derivation hierarchy r Act as private from the outside Class member declared as protected Acts as public member to Member functions and friends of derived class private member to The rest of the program

33. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 33 - C++ Inheritance C++ Class Derivation - Conversions Under Derivation There are four predefined conversions between a derived class and a public base class 1.Derived class object. Implicitly converted into a public base class object. 2.Derived class reference. Implicitly converted into a public base class reference. 3.Derived class pointer. Implicitly converted into a public base class pointer. 4.Pointer to a member of a base class. Implicitly converted to a pointer to that member in a publicly derived class.

34. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 34 - C++ Inheritance Apple a, *aPtr = &a;// Derived Class Fruit f, *fPtr = &f; // Base Class 1.a may be used anyplace f is used - contains a base class 2. a may be used as a reference anywhere a reference to f is used - contains a base class. 3.the pointer aPtr may be used anywhere fPtr is used - contains a base class 4.fp -> seeds can be used anywhere ap -> seeds is used - inherited from fruit. C++ Class Derivation - Conversions Under Derivation 1414 stem seeds this 1414 2323 stem seeds skin this

35. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 35 - C++ Inheritance C++ Class Derivation - Conversions Under Derivation Apple a, *aPtr = &a;// Derived Class Fruit f, *fPtr = &f; // Base Class 1.Fruit *fp = new Apple; Implicit conversion - 3 2a.Apple *ap = new Fruit; Error No implicit conversion Skin uninitialized and undefined Stem = 1 but *ap -> stem unitialized 2b.Apple *pa = (Apple *) new Fruit; Legal - Explicit conversion Explicit cast - Legal but dangereous seeds 1414 2323 stem skin fp -> stem ((Apple *) fp) -> stem

36. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 36 - C++ Inheritance Overloaded Functions with Class Type Arguments Overloaded Function Call Resolution Exact Match A class argument matches only a formal argument of its own class If class B is derived from class A Overload function f1 f1 (A a); f1 (B b); Then declare an instance of B B b1; f1 (b1); // is legal and resolvable

37. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 37 - C++ Inheritance Overloaded Functions with Class Type Arguments Overloaded Function Call Resolution Standard Conversions - Object Conversion A derived class Object, Reference, or Pointer is implicitly converted into a public base class type. If class B is derived from class A Overload function f1 f1 (A a); f1 (C c);// C is not in the derivation hierarchy Then declare an instance of B B b1; f1 (b1); // is legal and resolvable to the proper // function

38. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 38 - C++ Inheritance Overloaded Functions with Class Type Arguments Overloaded Function Call Resolution Standard Conversions - void Conversion A pointer of any class type is implicitly converted into a pointer of type void. If class B is derived from class A Overload function f1 f1 (C* &c); // C is not in the derivation hierarchy f1 (void* ); If class B is derived from class A Then declare an instance of B B b1; f1 (&b1); // is legal and resolvable to the proper // function

39. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 39 - C++ Inheritance Overloaded Functions with Class Type Arguments Overloaded Function Call Resolution Standard Conversions - Programmer Defined Conversion to: syntax operator typeName() { body } typeName - type to convert to from the class from: Use the constructor with a single argument syntax X::X ( typeName arg ) { body } typeName - type to convert from to the class

40. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 40 - C++ Inheritance Copy Constructors and Derivation If a copy constructor is not supplied for derived class a default copy constructor is generated Derived default copy constructor copies  Base and member objects By calling their copy constructors  Data members as a memcopy If a copy constructor is supplied must specify the desired copy constructors for  Base and member objects syntax DerivedClass X (const DerivedClass X& object) : BaseClass (object) object - the object being copied

41. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 41 - C++ Inheritance Over Riding Inherited Members When a function name is reused or inherited from multiple base classes - ambiguity results. Compiler tries to resolve any such conflicts…. Single Path Use the function in the most immediate scope for which the signatures are identical Multiple Paths Use the scope operator or virtual functions

42. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 42 - C++ Inheritance Multiple Base Classes A derived class can inherit from multiple base classes…. syntax class DerivedClassName : spec 0 base class 0, spec 1 base class 1,... spec n base class n, DerivedClassName - the class being derived Specification - specifies access to the base class members public protected private

43. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 43 - C++ Inheritance Multiple Base Classes Let: class A be derived from base classes B, C, and D B public C, D private 1.class A : public B, private C, D 2.class A : private C, public B, private D 3.class A : C, D, public B

44. Copyright 2006 Oxford Consulting, Ltd1 February 2006 - 44 - C++ Inheritance Multiple Base Classes- Inherited Member Initialization qIf the base class has only a default constructor Initialize the member values in the body of the derived class constructor qA constructor with arguments  The init list used to pass args to the base class constructors  Invocation is left to right, depth first syntax DerivedClass ( dCl args ) : BC0 (bC0 args), BC1 (bC1 args),...BCn ( bCn args), { DerivedClass constructor body }