C++面向对象程序设计双语教程（第3版）课件 class 12-Inheritance-3

ObjectivesTounderstandtheconceptofmultipleinheritanceTounderstandwhyinheritanceambiguityoccursinmultipleinheritanceToknowthemechanismofvirtualinheritance01ClassHierarchyandMultipleInheritance03VirtualInheritance02InheritanceAmbiguity01ClassHierarchyandMultipleInheritanceClassHierarchiesTreestructureofclasshierarchyLatticestructureofclasshierarchySingleinheritanceandmultilevelinheritanceMultipleinheritanceandhybridinheritanceMultipleInheritanceBed+sleep():void+weight:intSofa+watchTV():void+weight:intSofaBed+foldOut():voidAclasscanhavemorethanonedirectbaseclass.Theuseofmorethanimmediatebaseclassisusuallycalledmultipleinheritance.CasestudyTherearetheBed,SofaandSofaBedclassesinaclasshierarchy.DefinitionsofDerivedClassesinMultipleInheritanceclassSofaBed:publicSofa,publicBed{//…};Bed+sleep():void+weight:intSofa+watchTV():void+weight:intSofaBed+foldOut():voidSyntaxtodefineaderivedclassofmultipleinheritanceConstructorsandDestructorsofMultipleInheritanceclass

Bed{public:Bed(){}voidsleep(){cout<<"Sleep..\n";}intweight;};class

Sofa{public:Sofa(){}voidwatchTV(){ cout<<"WatchingTV..\n";}intweight;};class

SofaBed:public

Bed,public

Sofa{public:SofaBed(){}voidfoldOut(){ cout<<"Foldout..\n";}};intmain(){SofaBedsBed;sBed.sleep();sBed.watchTV();sBed.foldOut();return0;}DerivedconstructorwithoutparametersSofaBed():Bed(),Sofa(){}ConstructorsandDestructorsofMultipleInheritancederived’sconstructor:base1’sconstructor,base3’sconstructor,base2’sconstructor{}Destroyingderivedobjects’sequence:derivedclass->base3->base2->base1classderived:publicbase1,publicbase2,publicbase3{};Constructingderivedclassobjects’sequence:base1->base2->base3->derivedSyntaxtodefineaconstructorofthederivedclassSyntaxtodefineadestructorofthederivedclassConstructingderivedobjects’sequenceaccordingtodeclaringsequenceofbaseclasses.derived’sdestructor{}ConstructorsandDestructorofMultipleInheritanceclass

Bed{public:Bed(int

w):weight(w){}voidsleep(){cout<<"Sleep..\n";}intweight;};class

Sofa{public:Sofa(int

w):weight(w){}voidwatchTV(){ cout<<"WatchingTV..\n";}intweight;};class

SofaBed:public

Bed,public

Sofa{public:SofaBed(int

w):Bed(w),Sofa(w){}voidfoldOut(){ cout<<"Foldout..\n";}};intmain(){SofaBedsBed(5);sBed.sleep();sBed.watchTV();sBed.foldOut();return0;}Derivedconstructorwithparameters02InheritanceAmbiguity

InheritanceAmbiguityintmain(){SofaBedsBed(5);sBed.sleep();sBed.watchTV();sBed.foldOut();

return0;}cout<<sBed.weight;//errorcout<<sBed.Bed::weight;Bed’s

weight?Sofa’s

weight?MultipleinheritanceambiguitiesWhenthebaseclassesmayhavememberfunctionswiththesamename,thefunctioncallofderivedclassobjectleadstoambiguity.Bed+sleep():void+weight:intSofa+watchTV():void+weight:intSofaBed+foldOut():voidInheritanceAmbiguitySingleinheritancemultipleinheritanceBed+sleep():voidSofa+watchTV():voidSofaBed+foldOut():voidFurniture-weight:intFurniture-weight:intBed+sleep():void+weight:intSofa+watchTV():void+weight:intSofaBed+foldOut():voidInheritanceAmbiguityThediamondproblemoccursinalatticestructure.HowtoavoidduplicatedBaseClasses?Bed+sleep():voidSofa+watchTV():voidSofaBed+foldOut():voidFurniture-weight:intDuplicationInheritanceclass

Furniture{intweight;public:Furniture(int

w):weight(w){}intgetWeight(){returnweight;}};class

Bed:public

Furniture{public:Bed(int

w):Furniture(w){}voidsleep(){cout<<"Sleep..\n";}};class

Sofa:public

Furniture{public:Sofa(int

w):Furniture(w){}voidwatchTV(){cout<<"WatchingTV..\n";}};class

SofaBed:public

Bed,public

Sofa{public:SofaBed(int

w):Bed(w),Sofa(w){}voidfoldOut(){cout<<"Foldout..\n";}};intmain(){SofaBedsBed(5);sBed.sleep();sBed.watchTV();sBed.foldOut();return0;}Result:Sleep..WatchingTV..Foldout..Constructingfurniture...ConstructingBed...Constructingfurniture...ConstructingSofa...ConstructingSofaBed...DuplicationInheritanceProblem:theduplicationofBaseClassesintmain(){SofaBedsBed(5);sBed.sleep();sBed.watchTV();sBed.foldOut();return0;}cout<<sBed.getWeight()<<endl;//error:

ambiguitySleep..WatchingTV..Foldout..Constructingfurniture...ConstructingBed...Constructingfurniture...ConstructingSofa...ConstructingSofaBed...Howtoresolvethisissue?03VirtualInheritanceVirtualInheritanceclass

Furniture{intweight;public:Furniture(int

w):weight(w){}intgetWeight(){returnweight;}};class

Bed:virtualpublic

Furniture{public:Bed(int

w):Furniture(w){}voidsleep(){cout<<"Sleep..\n";}};class

Sofa:virtualpublic

Furniture{public:Sofa(int

w):Furniture(w){}voidwatchTV(){cout<<"WatchingTV..\n";}};Class

SofaBed:public

Bed,public

Sofa{public:SofaBed(int

w):Furniture(w),Bed(w),Sofa(w){}voidfoldOut(){cout<<"Foldout..\n";}};intmain(){SofaBedsBed(5);sBed.sleep();sBed.watchTV();sBed.foldOut();cout<<sBed.getWeight()<<endl;return0;}virtualinheritanceVirtualInheritanceBed+sleep():voidSofa+watchTV():voidSofaBed+foldOut():voidFurniture-weight:intVirtualinheritanceVirtualinheritanceConstructorandVirtualInheritanceClass

SofaBed:public

Bed,public

Sofa{public:SofaBed(int

w):Furniture(w),Bed(w),Sofa(w){}voidfoldOut(){cout<<"Foldout..\n";}};FurnitureBedSofaSofaBedConstructingsequence:intmain(){SofaBedsBed(5);sBed.sleep();sBed.watchTV();sBed.foldOut();cout<<sBed.getWeight()<<endl;return0;}VirtualInheritanceVirtualInheritanceisa

mechanismthatoffersawaytopreventmultiple“instances”ofagivenclassappearinginaninheritancehierarchywhenusingmultipleinheritances.

Virtualbaseclassesofferawaytosavespaceandavoidambiguitiesinclasshierarchiesthatusemultipleinheritances.Whenabaseclassisspecifiedasavirtualbase,itcanactasanindirectbasem