C++面向对象程序设计双语教程（第3版）课件 class 11-Inheritance-2

ObjectivesTounderstandinheritancefurtherTobeabletodefinederivedclassesindifferentinheritancemodes01MemberFunctionsofDerivedClasses03CaseStudy02InheritanceAccessControl01MemberFunctionsofDerivedClassesMemberfunctionsof

DerivedClassesclass

Employee{public:Employee(string

n,int

d){name=n;department=d;}voidprint()const{cout<<name<<department<<endl;}private:stringname;intdepartment;};class

Manager:public

Employee{public:Manager(string

n,int

d,string

rs):Employee(n,d),responsibility(rs){}private:stringresponsibility;};voidprint()const;Manager-responsibility:string+Manager(string,int,string)+management():voidEmployee-name:stringdepartment:string+Employee(string,int)+print():voidconstMemberFunctionsofDerivedClassesThememberfunctionsofthederivedclasscanalsobere-definedwhentheirnamesarethesameasonesofitsbaseclass.class

Manager:public

Employee{public:Manager(string&n,int

d,int

lvl):Employee(n,d),level(lvl){}voidprint()const;private:stringresponsibility;};void

Manager::print(){print();cout<<responsibility;}void

Manager::print(){Employee::print();cout<<responsibility;}void

Manager::print()const{cout<<name<<department;cout<<responsibility;}CannotaccesstheprivatemembersintheotherclassHowtodefinetheprintfunctioninclassManager?√MemberfunctionsofDerivedClassesvoid

Manager::print(){Employee::print();cout<<responsibility;}Functionoverridingisafeaturethat

allowsustouseafunctioninthederivedclassthatisalreadypresentinitsbaseclass.Whenyouwanttooverrideafunctionalityinthebaseclass,youusefunctionoverridingin

thederivedclass.Thismeansthattheimplementationofthebaseclassfunctionsismodified.FunctionOverridingFunctionOverridingvsOverloadingFunctionoverloadingprovidesmultipledefinitionsofthefunctionbychangingsignature,i.e.changenumbersofparametersanddatatypesofparameters,butthereturntypedoesn’tplayanyrole.Functionoverridingisredefinitionofthebaseclassfunctionwiththesamereturntypeandparameterlistinthederivedclass.voidprint();//okvoidprint(int);//okintprint(int);//errorstringprint(string);//okclass

base{public:voidfun(){cout<<

"base::fun()\n";}voidfun(int

a){cout<<

"base::fun(int)"

<<

a

<<endl;}};class

derived:public

base{public:voidfun(){cout<<

“derived::fun()\n";}voidfun(string

s){cout<<

"derived::fun(string)"

<<

s

<<endl;}};intmain(){baseb;b.fun();b.fun(4);derivedd;d.fun();d.fun("4");//d.fun(4);compileerrorreturn0;}OverridingmemberfunctionsOverloadingmemberfunctionsFunctionOverridingvsOverloading02InheritanceAccessControlAccessControlIfitisprivate,itsnamecanbeusedonlybymemberfunctionsandfriendsoftheclassinwhichitisdeclared.Ifitispublic,itsnamecanbeusedbyanyfunction.Ifitisprotected,itsnamecanbeusedonlybymemberfunctionsandfriendsoftheclassinwhichitisdeclaredandbymemberfunctionsandfriendsofclassesderivedfromthisclass.#Test-

a:int+

b:int#

c:intAccesscontrolinaclassareclassifiedintothreecategories:private,protectedorpublic.AccessControl–ProtectedMembersintmain(){Testta;ta.a=99;ta.b=100;ta.c=50;cout<<ta.geta()<<endl;cout<<ta.getb()<<endl;cout<<ta.c<<endl;return0;}//error-

private//error-protected//ok-publicTest-

a:int+

b:int#

c:intclass

Test{inta;protected:intb;public:intc;Test(){a=b=c=10;}intgeta(){returna;}intgetb(){returnb;}};class

dTest:public

Test{public:dTest():Test(){dt=20;}voidreset(){a=20;//errorb=20;}protected:intdt;};intmain(){dTestdtObj;cout<<dtObj.geta();cout<<dtObj.getb();cout<<dtObj.c;dtObj.reset();cout<<dtObj.getb();return0;}InheritanceAccessControlWhencreatingaderivedclassfromabaseclass,youcanusedifferentaccessspecifierstoinheritthedatamembersofthebaseclass.Thederivedclasscanaccessallthenon-privatemembersofitsbaseclass.Andthebaseclassmembersthatarenotaccessibletothememberfunctionsofderivedclassesshouldbedeclaredprivateinthebaseclass.Theaccessspecifiersthatareusedarepublic,privateandprotected.Whenderivingaclassfromabaseclass,thebaseclassmaybeinheritedthroughpublic,privateandprotectedinheritance.PublicInheritancesWheninheritingaclassfromapublicbaseclass,i.e.publicderivation,publicmembers

ofthebaseclassbecomepublicmembers

ofthederivedclass,protectedmembersofthebaseclassbecomeprotectedmembers

ofthederivedclass,andprivatemembersofthebaseclasskeepprivatemembersofthederivedclass.Publicderivationmakesthederivedclassasubtypeofitsbaseclass,itisthemostcommonformofderivation.PublicInheritanceclass

RichMan{public:RichMan();~RichMan();intcompany;//公司能被自己(基类),创业伙伴(友元),儿子(子类),其他人(外部)都可以访问private://钱和车子能被自己(基类)，创业伙伴(友元)可以访问.儿子和外人都不给开int

money;intcar;protected:int

house;//房子能被自己(基类)，创业伙伴(友元)可以访问，儿子(子类)也可以访问，外人是不可以访问};RichMancar:intmoney:int#house:int+company:int+RichMan()+~RichMan()class

LittleRichMan:public

RichMan{public:LittleRichMan();~LittleRichMan();};PublicInheritanceclass

LittleRichMan:public

RichMan{public:LittleRichMan();~LittleRichMan();};publicclass

LittleRichMan:public

RichMan{public:LittleRichMan();~LittleRichMan();intm_company;//baseclassprotected:

intm_house;//baseclassprivate:

intcar;//baseclass

intmoney;//baseclass};LittleRichMan+LittleRichMan()+~LittleRichMan()publicRichMancar:intmoney:int#house:int+company:int+RichMan()+~RichMan()ProtectedInheritancesWhenderivingfromaprotectedbaseclass,i.e.protectedderivation,publicandprotectedmembersofthebaseclassbecomeprotectedmembersofthederivedclass,andprivatemembersofthebaseclasskeepprivatemembersofthederivedclass.Protectedderivationisusefulinclasshierarchiesinwhichfurtherderivationisthenorm.ProtectedInheritancesclass

RichMan{public:RichMan();~RichMan();intcompany;//公司能被自己(基类),创业伙伴(友元),儿子(子类),其他人(外部)都可以访问private://钱和车子能被自己(基类)，创业伙伴(友元)可以访问.儿子和外人都不给开int

money;intcar;protected:int

house;//房子能被自己(基类)，创业伙伴(友元)可以访问，儿子(子类)也可以访问，外人是不可以访问};class

LittleRichMan:protected

RichMan{public:LittleRichMan();~LittleRichMan();};ProtectedInheritanceclass

LittleRichMan:protected

RichMan{public:LittleRichMan();~LittleRichMan();};protectedclass

LittleRichMan:protected

RichMan{public:LittleRichMan();~LittleRichMan();protected:int

m_company;//baseclassint

m_house;//baseclassprivate:int

car;//baseclassint

money;//baseclass};LittleRichMan+LittleRichMan()+~LittleRichMan()protectedRichMancar:intmoney:int#house:int+company:int+RichMan()+~RichMan()PrivateInheritancesWhenwederivefromaprivatebaseclass,i.e.privatederivation,publicandprotectedmembersofthebaseclassbecomeprivatemembersofthederivedclass.Privatemembersofthebaseclasskeepprivatemembersofthederivedclass.Privatederivationismostusefulwhendefiningaclassbyrestrictingtheinterfacetobasesothat

strongerguaranteescanbeprovided.PrivateInheritancesclass

RichMan{public:RichMan();~RichMan();intcompany;//公司能被自己(基类),创业伙伴(友元),儿子(子类),其他人(外部)都可以访问private://钱和车子能被自己(基类)，创业伙伴(友元)可以访问.儿子和外人都不给开int

money;intcar;protected:int

house;//房子能被自己(基类)，创业伙伴(友元)可以访问，儿子(子类)也可以访问，外人是不可以访问};class

LittleRichMan:private

RichMan{public:LittleRichMan();~LittleRichMan();};PrivateInheritanceclass

LittleRichMan:private

RichMan{public:LittleRichMan();~LittleRichMan();};privateclass

LittleRichMan:private

RichMan{public:LittleRichMan();~LittleRichMan();private:intm_company;//baseclassintm_house;//baseclassprivate:intcar;//baseclassintmoney;//baseclass};LittleRichMan+LittleRichMan()+~LittleRichMan()privateRichMancar:intmoney:int#house:int+company:int+RichMan()+~RichMan()DifferentInheritancesBaseclassAccesscontrolDerivedclassAccesscontrolGeneralusersprivateinheritanceprivateprivateNANAprotectedprivateANApublicprivateANAprotectedinheritanceprivateprivateNANAprotectedprotectedANApublicprotectedANApublicinheritanceprivateprivateNANAprotectedprotectedANApublicpublicAA03CaseStudyCaseStudyDesignasystemthatopensdifferentpostfixedfiles,e.g..txt,.pngandetc.textFile+openFile():voidFile#filename:string+openFile():voidbmpFile+openFile():voidDataabstractionForatextfilewith.txt,data:filenamefunction:openfileForanimagefilewith.png,data:filenamefunction:openfileAbstractcommonfeaturesCaseStudyclass

File{public:File(string&filename){fileName=filename;}voidopenFile(){cout<<"Openfile!\n";}protected:stringfileName;};class

textFile