1、C+ Programming CHAPTER 8 INHERITANCE18.1 Introduction8.2 Basic Concepts and Syntax8.3 Public, Private, and Protected Inheritance8.4 Multiple Inheritance 8.5 Constructors and Destructors Under Inheritance8.6 Name Hiding8.7 Virtual Inheritance28.1 IntroductionIn C+, we can build a new class by derivin

2、g the new class from an already existing class. The mechanism for this derivation is inheritance, and the derived class is said to be inherited from the original class.38.1 Introductionsalon cartruckestate carcarvehicle48.1 IntroductionInheritance promotes code reuse because the code in the base cla

3、ss is inherited by the subclass and thus need not be rewritten. You can reuse code by creating new classes, but instead of creating them from scratch, you use existing classes that someone else has built and debugged.58.1 IntroductionInheritance also provides a mechanism to express the natural relat

4、ionships among the components of a program.68.1 Introductionmonkeyliontigerleopardcatbirdanimal78.1 IntroductionInheritance is required for polymorphism in which the particular method to invoke depends on the class to which the object belongs, but the class to which the object belongs is not known u

5、ntil the program is executing.88.2 Basic Concepts and SyntaxSyntax:class DerivedClass：InheritanceMode BaseClasspublic:/protected:/private:/;98.2 Basic Concepts and SyntaxExample:class Penpublic:enum ink Off, On;void set_status( ink );void set_location( int, int );private:int x;int y;ink status;108.2

6、 Basic Concepts and Syntaxclass CPen : public Penpublic:void set_color(int);private:int color;118.2 Basic Concepts and Syntaxint main()CPen pen1;return 0;PenCPenCPen128.2 Basic Concepts and SyntaxRemarks:A) The members, which are public in the base class, are also public in the derived class.B) The

7、private member in a base class is visible only in the base class. 138.3 Public, Private, and Protected InheritancePublic InheritancePublic InheritanceRules:A) The public members and protected members in the base class are also public and protected in the derived class, but the private members in the

8、 base class cant be accessed in the derived class.148.3 Public, Private, and Protected InheritancePublic InheritanceB) The public members and the protected members in the base class can be accessed by the methods of the derived class, but the private members cant be accessed by the methods of derive

9、d class.C) Only the public members in the base class can be accessed by the objects of the derived class.158.3 Public, Private, and Protected InheritancePublic InheritanceExample:class Point/base classpublic:void InitP(float xx=0, float yy=0) X=xx;Y=yy;void Move(float xOff, float yOff) X+=xOff;Y+=yO

10、ff;float GetX() return X;float GetY() return Y;private:float X,Y;168.3 Public, Private, and Protected InheritancePublic Inheritanceclass Rectangle: public Point /derived classpublic:/ new public method of Rectanglevoid InitR(float x, float y, float w, float h)InitP(x,y);W=w;H=h;/invoke the public me

11、thod of base /classfloat GetH() return H;float GetW() return W;private:/ new private members of Rectanglefloat W,H;constructor and destructor of Point are not inherited!178.3 Public, Private, and Protected InheritancePublic Inheritance#include#includeusing namespace std;int main() Rectangle rect;rec

12、t.InitR(2,3,20,10);/access the public members of the base class by object of derived classrect.Move(3,2); coutrect.GetX(), rect.GetY(),rect.GetW(),rect.GetH()endl;return 0;Output：5，5，20，10188.3 Public, Private, and Protected InheritancePublic InheritanceRemark：The default constructor and destructor

13、can not be inherited.198.3 Public, Private, and Protected InheritancePrivate InheritancePrivate InheritanceRules:A) The public members and protected members in the base class are both private in the derived class, but the private members in the base class can not be accessed in the derived class.208

14、.3 Public, Private, and Protected InheritancePrivate InheritanceB) The public members and the protected members in the base class can be accessed by the methods of the derived class, but the private members cant be access by the methods of derived class.C) All the members in the base class cant be a

15、ccessed by the objects of the derived class.21Example:class Rectangle: private Pointpublic:/ new public methods of Rectangle /access the public members of the base classvoid InitR(float x, float y, float w, float h)InitP(x,y);W=w;H=h; /redeclare the interface of base class, why? void Move(float xOff

16、, float yOff) Point:Move(xOff,yOff);float GetX() return Point:GetX();float GetY() return Point:GetY();float GetH() return H;float GetW() return W;private:/ new private members of Rectanglefloat W,H;22#include#includeusing namespace std;int main() /only the members of derived class /can be access by

17、objects of derived classRectangle rect;rect.InitR(2,3,20,10); rect.Move(3,2);coutrect.GetX(), rect.GetY(),rect.GetW (),rect.GetH ()endl;return 0;Output：5，5，10，20238.3 Public, Private, and Protected InheritanceProtected InheritanceProtected InheritanceRules:A) The public members and protected members

18、 in the base class are both protected in the derived class, but the private members in the base class can not be accessed in the derived class.248.3 Public, Private, and Protected InheritanceProtected InheritanceB) The public members and the protected members in the base class can be accessed by the

19、 methods of the derived class, but the private members cant be access by the methods of derived class.C) All the members in the base class cant be accessed by the objects of the derived class.258.3 Public, Private, and Protected InheritanceProtected InheritanceTo the objects of the derived class, pr

20、otected inheritance is the same with private inheritance. To the derived class, protected inheritance is the same with public inheritance.268.3 Public, Private, and Protected InheritanceProtected InheritanceExample:class Aprotected:int x;int main()A a;a.x=5; /wrong278.3 Public, Private, and Protecte

21、d InheritanceProtected InheritanceExample:class A protected:int x;class B: public Apublic:void Function();void B:Function()x=5; /right288.3 Public, Private, and Protected InheritanceProtected Inheritancecant accessprivateprivateprivateprivateprotectedprivateprivatepubliccant accessprotectedprivatepr

22、otectedprotectedprotectedprotectedprotectedpubliccant accesspublicprivateprotectedpublicprotectedpublicpublicpublicin derived classinheritance mode members in base class298.3 Public, Private, and Protected InheritanceProtected InheritanceExample:Ch8-2.text Ch8-2 answer.txt308.3 Public, Private, and

23、Protected InheritanceCompatible RulesCompatible RulesAn object of derived class, which is public inherited from the base class, can be use as a object of base class:A) Objects of base class can be assigned by the object of derived class.B) References of base class can be initialized by the object of

24、 derived class.318.3 Public, Private, and Protected Inheritance Compatible RulesC) Pointers of base class can be assigned by the pointer of derived class.D) Only members of base class can be accessed by the pointers and objects of base class.328.3 Public, Private, and Protected Inheritance Compatibl

25、e RulesExample:class Base;class Derived: public Base;Base b;Derived d;b=d;Derived d;Base &b=d; Derived d;Base *bptr=&d;Derived *dptr;Base *bptr=dptr;338.3 Public, Private, and Protected Inheritance Compatible RulesExample:#include using namespace std;class B0/Base class public:void display()coutB0:d

26、isplay()endl; ;348.3 Public, Private, and Protected Inheritance Compatible Rulesclass B1: public B0public:void display()coutB1:display()endl;class D1: public B1public:void display()coutD1:display()display();358.3 Public, Private, and Protected Inheritance Compatible Rulesvoid main()B0 b0;/object of

27、B0B1 b1;/ object of B1D1 d1;/ object of D1B0 *p;/ pointer of B0p=&b0;/ point to object of B0fun(p);p=&b1;/point to object of B1fun(p);p=&d1;/ point to object of D1fun(p);Output:B0:display()B0:display()B0:display()368.3 Public, Private, and Protected Inheritance Compatible RulesExercise:#include clas

28、s Basepublic: void f()cout “excuting Base:f() n”; int a;class Derived :public Basepublic: void f()cout“executing Derived:f()”; int a;37int main()Base x;x.a=20;x.f();cout“x.a=”x.aendl;Derived y;y.a=40;y.Base:a=60;y.f();y.Base:f();cout“y.a=”y.aendl;cout“y.Base:a=”y.Base:aendl;Base z=y;cout“z.a=”z.aend

29、l;return 0;Output:executing Base:f()x.a=20executing Derived:f()executing Base:f()y.a=40y.Base:a=60z.a=60388.4 Multiple Inheritance You can inherit from one class, so it would seem to make sense to inherit from more than one class at a time. In multiple inheritance, a derived class has multiple base

30、classes.398.4 Multiple Inheritance Syntax:class DerivedClass：InheritanceMode BaseClass1, InheritanceMode BaseClass2, . /;Remark:The rules of inheritance and access dont change from a single to a multiple inheritance hierarchy.40Example:class Apublic:void setA(int);void showA();private:int a;class Bp

31、ublic:void setB(int);void showB();private:int b;class C : public A, private Bpublic:void setC(int, int, int);void showC();private:int c;41void A:setA(int x) a=x; void B:setB(int x) b=x; void C:setC(int x, int y, int z) setA(x); setB(y); c=z; /.int main()C obj;obj.setA(5);obj.showA();obj.setC(6,7,9);

32、obj.showC();/ obj.setB(6); wrong, why?/ obj.showB(); wrong, why?return 0;428.5 Constructors and Destructors Under InheritanceConstructors under InheritanceConstructors under InheritanceRules:A) Constructors of base class cant be inherited.B) Members of derived class should be initialized by its own

33、constructors. Members of base class should be initialized by the constructors of base class.C) The arguments of the constructors of base class should be offered by the constructor of derived class.438.5 Constructors and Destructors Under InheritanceConstructors under InheritanceSingle InheritanceSyn

34、tax:DerivedClass: DerivedClass (ArgumentListOfBase, ArgumentListOfDdrived):BaseClass(ArgumentListOfBase) /；448.5 Constructors and Destructors Under InheritanceConstructors under InheritanceOrder of Constructor calls in Single Inheritance1) Constructors of base class.2) Constructors of data members i

35、n derived class.3) Constructors of derived class.45Example:#includeusing namespace std;class Bpublic:B();B(int i);B();void Print() const;private:int b;B:B()b=0;coutBs default constructor called. endl;B:B(int i)b=i; coutBs constructor called. endl;B:B()coutBs destructor called. endl; void B:Print() c

36、onstcoutbendl; 46class C:public Bpublic:C();C(int i,int j);C();void Print() const;private:int c;C:C()c=0;coutCs default constructor called. endl;C:C(int i,int j):B(i)c=j;coutCs constructor called.endl;C:C()coutCs destructor called.endl; void C:Print() constB:Print();coutcendl; 47void main()C obj(5,6

37、);obj.Print();Output:Bs constructor called.Cs constructor called.56Cs destructor called.Bs destructor called.Question:Whats the effect of “C:C(int i,int j):B(i)”?488.5 Constructors and Destructors Under InheritanceConstructors under InheritanceMultiple InheritanceSyntax:DerivedClass: DerivedClass (A

38、rgumentListOfBase1, ArgumentListOfBaseN,ArgumentListOfDdrived):BaseClass1(ArgumentListOfBase1), BaseClassN(ArgumentListOf BaseN)BaseClassn(ArgumentListOfBaseN) /；498.5 Constructors and Destructors Under InheritanceConstructors under InheritanceArguments Offering Rules:A) If the constructors of base

39、class need no arguments, constructors of derived class can be no arguments.B) If the constructors of base class need arguments, constructors of derived class should offer arguments to them.508.5 Constructors and Destructors Under InheritanceConstructors under InheritanceOrder of Constructor calls in

40、 Multiple Inheritance:1) Constructors of base classes, in order of their declaration.2) Constructors of data members in derived class, in order of their declaration.3) Constructors of derived class.518.5 Constructors and Destructors Under InheritanceConstructors under InheritanceExample:code.txt. co

41、de-answer.txt528.5 Constructors and Destructors Under InheritanceConstructors under InheritanceCopy ConstructorsRules:A) If the default copy constructor is invoked by the object of derived class, the default copy constructor of base class is invoked automatically.B) If there is a user-defined copy c

42、onstructor of derived class, it should offer arguments to the copy constructor of base class.538.5 Constructors and Destructors Under InheritanceConstructors under InheritanceExample:C:C(C &c1):B(c1)/54Example:#include using namespace std;class B1/base class B1public: B1(int i) coutconstructing B1 i

43、endl; ;class B2/ base class B2public: B2(int j) coutconstructing B2 jendl; ;class B3/ base class B3public: B3() coutconstructing B3 *endl; ;55class C: public B2, public B1, public B3 public: C(int a, int b, int c, int d): B1(a),memberB2(d),memberB1(c),B2(b) private:B1 memberB1;B2 memberB2;B3 memberB

44、3;void main()C obj(1,2,3,4); Output:constructing B2 2constructing B1 1constructing B3 *constructing B1 3constructing B2 4constructing B3 *568.5 Constructors and Destructors Under InheritanceDestructors under InheritanceRules:A) Destructors cant be inherited.B) Order of destructors is opposition of c

45、onstructors.57Example:#include using namespace std;class B1/base class B1 public:B1(int i) coutconstructing B1 iendl;B1() coutdestructing B1 endl;class B2/base class B2public:B2(int j) coutconstructing B2 jendl;B2() coutdestructing B2 endl;class B3/base class B3public:B3()coutconstructing B3 *endl;B

46、3() coutdestructing B3 endl;58class C: public B2, public B1, public B3public: C(int a, int b, int c, int d): B1(a),memberB2(d),memberB1(c),B2(b)private: B1 memberB1; B2 memberB2; B3 memberB3;void main() C obj(1,2,3,4); Output:constructing B2 2constructing B1 1constructing B3 *constructing B1 3constr

47、ucting B2 4constructing B3 *destructing B3destructing B2destructing B1destructing B3destructing B1destructing B2598.6 Name HidingIf a derived class adds a member with the same name as the member in the base class, the local member hides the inherited member. 60Example:#include using namespace std;cl

48、ass B1/base classB1 public:int nV;void fun() coutMember of B1endl;class B2/base class B2 public:int nV;void fun() coutMember of B2endl;class D1: public B1, public B2 public:int nV;/same name with base classvoid fun() coutMember of D1endl; /same name with base class;61void main()D1 d1;d1.nV=1; /membe

49、r of D1 is accessedd1.fun(); d1.B1:nV=2;/member of B1 is accessedd1.B1:fun();d1.B2:nV=3;/member of B2 is accessedd1.B2:fun();628.7 Virtual InheritanceAmbiguityAmbiguityIn multiple inheritance, ambiguity is a problem.638.7 Virtual Inheritance AmbiguityExample:class Apublic:void f();class Bpublic:void

50、 f();void g();class C: public A, piblic B public: void g(); void h();Given the declaration:C c1;c1.f(); / wrong, ambiguousc1.g(); / right, namehiding648.7 Virtual Inheritance AmbiguitySolutions to ambiguitySolution1:Scopingc1.A:f()orc1.B:f()658.7 Virtual Inheritance AmbiguitySolution2:Name Hidingcla

51、ss C: public A, piblic B public:void g();void h();void f1()A:f();void f2()B:f();668.7 Virtual InheritanceVirtual Base ClassesVirtual Base ClassMultiple inheritance hierarchies can be complex, which may lead to the situation in which a derived class inherits multiple times from the same indirect base

52、 class.678.7 Virtual InheritanceVirtual Base ClassesExample:class B public:int b;class B1 : public Bprivate:int b1;class B2 : public Bprivate:int b2;class C : public B1,public B2public:int f();private:int d;688.7 Virtual InheritanceVirtual Base ClassesBB1B2C698.7 Virtual InheritanceVirtual Base Clas

53、sesbb1bb2dmembers of Bmembers of Bmembers of B1members of B2members of C708.7 Virtual InheritanceVirtual Base Classesambiguous:C c;c.bc.B:bunambiguous:c.B1:bc.B2:bHow to solve the data redundancy?718.7 Virtual InheritanceVirtual Base ClassesSyntax:class DerivedClass:virtual InheritanceMode BaseClass

54、/Remark:In multiple inheritance hierarchies, derived class has only one single copy of the base class by using the keyword virtual.728.7 Virtual InheritanceVirtual Base ClassesExample:class B private: int b;class B1 : virtual public B private: int b1;class B2 : virtual public B private: int b2;class

55、 C : public B1, public B2 private: float d;C cobj;cobj.b;/there is only one copy of B in C738.7 Virtual InheritanceVirtual Base ClassesBB1B2Cb1b2dB1 members B2 membersC objectbB membersonly one copy of data member and methods 748.7 Virtual InheritanceVirtual Base ClassesExample:D1nV :int nVd:intB1:n

56、V1:intB2:nV2:intfund():voidfun():voidB1nV1 :intB2nV2 :intD1nVd :intfund():void B0nV :intfun()758.7 Virtual InheritanceVirtual Base Classes#include using namespace std;class B0/base class B0 public:int nV;void fun()coutMember of B0endl;class B1: virtual public B0 /virtual inherited from B0 public:int nV1;class B2: virtual public B0 / virtual inherited from B0 public:int nV2;7