實(shí)驗(yàn)52 參考答案

試驗(yàn)5(2)類的繼承與派生參照答案一、試驗(yàn)?zāi)康呐c試驗(yàn)規(guī)定（1）掌握單繼承和多重繼承下派生類的定義措施，理解基類組員在不一樣的繼承方式下不一樣的訪問屬性。（2）對(duì)的定義派生類的構(gòu)造函數(shù)與析構(gòu)函數(shù)，理解定義一種派生類對(duì)象時(shí)構(gòu)造函數(shù)、析構(gòu)函數(shù)的調(diào)用次序。（3）理解同名沖突的產(chǎn)生原因，會(huì)使用虛基類來處理第三類同名沖突問題，并理解引入虛基類后構(gòu)造函數(shù)、析構(gòu)函數(shù)的調(diào)用次序。（4）理解賦值兼容的有關(guān)使用措施。二、試驗(yàn)內(nèi)容題目1：定義一種車基類，派生出自行車類和汽車類，并以自行車類和汽車類為基類共同派生出摩托車類，每個(gè)類都要定義帶有參數(shù)的構(gòu)造函數(shù)。自行車類分別使用private、protected、public三種方式來繼承車基類，觀測(cè)基類組員在派生類中的訪問屬性；觀測(cè)自行車類、汽車類和摩托車類對(duì)象定義時(shí)構(gòu)造、析構(gòu)函數(shù)的調(diào)用次序。最終將車基類定義為虛基類再觀測(cè)程序運(yùn)行成果。題目的詳細(xì)規(guī)定如下。①定義基類Vehicle，它具有兩個(gè)保護(hù)組員變量：MaxSpeed、Weight，有3個(gè)公有的組員函數(shù)：Run()、Stop()、Show()，以及帶參數(shù)的構(gòu)造函數(shù)、析構(gòu)函數(shù)；再定義一種從Vehicle公有繼承的Bicycle類，增長(zhǎng)保護(hù)屬性的組員變量Height，定義Bicycle類的構(gòu)造函數(shù)、析構(gòu)函數(shù)，改造Show函數(shù)，用于輸出本類中的完整信息。main()函數(shù)中定義Bicycle類對(duì)象，觀測(cè)構(gòu)造函數(shù)和析構(gòu)函數(shù)的執(zhí)行次序，以及各組員函數(shù)的調(diào)用。使用跟蹤的措施觀測(cè)程序運(yùn)行的每一步究竟調(diào)用的是哪一種函數(shù)。②在上一步基礎(chǔ)上，將繼承方式分別修改為protected和private，再重新編譯，觀測(cè)這時(shí)的報(bào)錯(cuò)信息并進(jìn)行分析。③將Bicycle類的繼承方式恢復(fù)為public，代碼回到①的狀態(tài)，再在Bicycle類下面增長(zhǎng)一種第二層汽車類Car的定義，Car也是公有繼承基類Vehicle，其中增長(zhǎng)了一種保護(hù)組員變量SeatNum，表達(dá)汽車有幾種座位，其定義方式與類Bicycle類似。主函數(shù)中定義該類對(duì)象，觀測(cè)運(yùn)行成果。④在上一步的基礎(chǔ)上，再定義一種第三層類MotorCycle，該類以公有方式繼承了第二層的Bicycle和Car類。定義其構(gòu)造函數(shù)，要調(diào)用兩個(gè)直接基類的構(gòu)造函數(shù)，再改造函數(shù)Show()，輸出所有四個(gè)組員變量的信息。主函數(shù)中只定義類MotorCycle的對(duì)象并調(diào)用對(duì)應(yīng)的函數(shù)，代碼請(qǐng)參照試驗(yàn)指導(dǎo)1的④。程序進(jìn)行編譯，會(huì)產(chǎn)生4個(gè)錯(cuò)誤、8個(gè)警告，由于存在二義性問題，在同名組員前增長(zhǎng)“基類名：：”以消除二義性直到程序?qū)Φ?，觀測(cè)運(yùn)行成果。⑤再將代碼恢復(fù)至上一步未修改前，即存在4個(gè)錯(cuò)誤、8個(gè)警告的狀態(tài)，再作一定的修改，將Vehicle申明為虛基類以消除二義性，同步修改第三層類的構(gòu)造函數(shù)，其他代碼不變，詳細(xì)請(qǐng)參照試驗(yàn)指導(dǎo)1的⑤。觀測(cè)運(yùn)行成果，理解此時(shí)構(gòu)造函數(shù)、析構(gòu)函數(shù)的調(diào)用次序及用虛基類消除二義性的原理。參照程序如下：#include<iostream>usingnamespacestd;classVehicle //定義基類{protected: intMaxSpeed; //最大速度 intWeight; //重量public: Vehicle(intm,intw)//初始化組員變量的值 {MaxSpeed=m;Weight=w; cout<<"ConstructingVehicle...\n"; } ~Vehicle() { cout<<"DestructingVehicle...\n"; } voidRun() { cout<<"Thevehicleisrunning!\n"; } voidStop() { cout<<"Pleasestoprunning!\n"; } voidShow() { cout<<"It\'smaxspeedis:"<<MaxSpeed<<endl; cout<<"It\'sweightis:"<<Weight<<endl; }};classBicycle:publicVehicle //定義派生類，公有繼承{protected: intHeight; //高度，單位：厘米public: Bicycle(intm,intw,inth):Vehicle(m,w) //調(diào)用基類構(gòu)造函數(shù) { Height=h; //為本類中新增組員提供初始值 cout<<"ConstructingBicycle...\n"; } ~Bicycle() { cout<<"DestructingBycycle...\n"; } voidShow() //改造基類的Show函數(shù) { Vehicle::Show();//調(diào)用基類Show輸出MaxSpeed和Weight值 cout<<"It\'sHeightis:"<<Height<<endl; //輸出本類高度 }};intmain(){ Bicycleb(120,2,4); //定義派生類對(duì)象 b.Run(); //觀測(cè)構(gòu)造、析構(gòu)函數(shù)調(diào)用次序 b.Stop(); b.Show(); return0;}運(yùn)行成果：ConstructingVehicle...ConstructingBicycle...Thevehicleisrunning!Pleasestoprunning!It'smaxspeedis:120It'sweightis:2It'sHeightis:4DestructingBycycle...DestructingVehicle...Pressanykeytocontinue②在上一步基礎(chǔ)上，將繼承方式分別修改為protected和private，再重新編譯，觀測(cè)這時(shí)的報(bào)錯(cuò)信息并進(jìn)行分析。答：繼承方式是private或protected后，main函數(shù)中的語句：b.Run();b.Stop();等均不能通過編譯，由于基類中的組員函數(shù)都是派生類的私有的或保護(hù)的組員函數(shù)，類外用派生類對(duì)象都不能再調(diào)用。③將Bicycle類的繼承方式恢復(fù)為public，代碼回到①的狀態(tài)，再在Bicycle類下面增長(zhǎng)一種第二層汽車類Car的定義，Car也是公有繼承基類Vehicle，其中增長(zhǎng)了一種保護(hù)組員變量SeatNum，表達(dá)汽車有幾種座位，其定義方式與類Bicycle類似。主函數(shù)中定義該類對(duì)象，觀測(cè)運(yùn)行成果。指導(dǎo)：在Bicycle類下面增長(zhǎng)Car類的定義，參照如下代碼，劃線部分自己完畢。classCar:publicVehicle //定義派生類Car，公有繼承{public: intSeatNum; //座位數(shù) Car(intm,intw,ints):（8） //調(diào)用基類構(gòu)造函數(shù) { （9） //為本類中新增組員提供初始值 cout<<"ConstructingCar...\n"; } ~Car() { cout<<"DestructingCar...\n"; } voidShow() //改造基類的Show函數(shù) { （10） //調(diào)用基類Show輸出MaxSpeed和Weight值 （11） //輸出本類座位數(shù) }};在主函數(shù)增長(zhǎng)Car類對(duì)象的定義并調(diào)用對(duì)應(yīng)函數(shù)，主函數(shù)代碼如下。intmain(){ Bicycle（12） //定義自行車類對(duì)象 b.Run(); b.Stop(); b.Show(); Car（13） //定義汽車類對(duì)象 c.Run(); c.Stop(); c.Show(); return0;}參照程序如下：classCar:publicVehicle //定義派生類Car，公有繼承{protected: intSeatNum; //座位數(shù)public: Car(intm,intw,ints):Vehicle(m,w) //調(diào)用基類構(gòu)造函數(shù) { SeatNum=s; //為本類中新增組員提供初始值 cout<<"ConstructingCar...\n"; } ~Car() { cout<<"DestructingCar...\n"; } voidShow() //改造基類的Show函數(shù) { Vehicle::Show(); //調(diào)用基類Show輸出MaxSpeed和Weight值 cout<<"It\'sSeatNumis:"<<SeatNum<<endl; //輸出本類座位數(shù) }};intmain(){ Bicycleb(50,2,400); //定義自行車類對(duì)象 b.Run(); b.Stop(); b.Show(); Carc(120,,5); //定義汽車類對(duì)象 c.Run(); c.Stop(); c.Show(); return0;}運(yùn)行成果為：ConstructingVehicle...ConstructingBicycle...Thevehicleisrunning!Pleasestoprunning!It'smaxspeedis:50It'sweightis:2It'sHeightis:400ConstructingVehicle...ConstructingCar...Thevehicleisrunning!Pleasestoprunning!It'smaxspeedis:120It'sweightis:It'sSeatNumis:5DestructingCar...DestructingVehicle...DestructingBycycle...DestructingVehicle...Pressanykeytocontinue④在上一步的基礎(chǔ)上，再定義一種第三層類MotorCycle，該類以公有方式繼承了第二層的Bicycle和Car類。定義其構(gòu)造函數(shù)，要調(diào)用兩個(gè)直接基類的構(gòu)造函數(shù)，再改造函數(shù)Show()，輸出所有四個(gè)組員變量的信息。主函數(shù)中只定義類MotorCycle的對(duì)象并調(diào)用對(duì)應(yīng)的函數(shù)，代碼請(qǐng)參照試驗(yàn)指導(dǎo)1的④。程序進(jìn)行編譯，會(huì)產(chǎn)生4個(gè)錯(cuò)誤、8個(gè)警告，由于存在二義性問題，在同名組員前增長(zhǎng)“基類名：：”以消除二義性直到程序?qū)Φ?，觀測(cè)運(yùn)行成果。指導(dǎo)：增長(zhǎng)的第3層類MotorCycle及修改后來的main()函數(shù)。classMotorCycle:publicBicycle,publicCar //第3層類，從第2層兩個(gè)類公有繼承{public: MotorCycle(intm,intw,inth,ints):（14） //調(diào)用兩基類構(gòu)造函數(shù) { cout<<"ConstructingMotorCycle...\n"; } ~MotorCycle() { cout<<"DestructingMotorCycle...\n"; } voidShow() //輸出4個(gè)組員變量的信息，需消除二義性 { cout<<"It\'smaxspeedis:"<<MaxSpeed<<endl;//錯(cuò)誤 cout<<"It\'sweightis:"<<Weight<<endl; //錯(cuò)誤 cout<<"It\'sheightis:"<<Height<<endl; cout<<"It\'sseatnumis:"<<SeatNum<<endl; }};intmain(){ MotorCycle（15） //定義摩托車類對(duì)象 mc.Run(); //錯(cuò)誤 mc.Stop(); //錯(cuò)誤 mc.Show(); return0;}程序?yàn)椋篶lassMotorCycle:publicBicycle,publicCar//第3層類，從第2層兩個(gè)類公有繼承{public: MotorCycle(intm,intw,inth,ints):Bicycle(m,w,h),Car(m,w,s)//調(diào)用兩基類構(gòu)造函數(shù) { cout<<"ConstructingMotorCycle...\n"; } ~MotorCycle() { cout<<"DestructingMotorCycle...\n"; } voidShow()//輸出4個(gè)組員變量的信息，需消除二義性 { cout<<"It\'smaxspeedis:"<<MaxSpeed<<endl;//錯(cuò)誤 cout<<"It\'sweightis:"<<Weight<<endl; //錯(cuò)誤 cout<<"It\'sheightis:"<<Height<<endl; cout<<"It\'sseatnumis:"<<SeatNum<<endl; }};intmain(){ MotorCyclemc(120,1000,2,2); //定義摩托車類對(duì)象 mc.Run(); //錯(cuò)誤 mc.Stop(); //錯(cuò)誤 mc.Show(); return0;}編譯出錯(cuò)：E:\-(2)\C++教學(xué)\教案\Text1.cpp(113):errorC2385:'MotorCycle::MaxSpeed'isambiguousE:\-(2)\C++教學(xué)\教案\Text1.cpp(113):warningC4385:couldbethe'MaxSpeed'inbase'Vehicle'ofbase'Bicycle'ofclass'MotorCycle'E:\-(2)\C++教學(xué)\教案\Text1.cpp(113):warningC4385:orthe'MaxSpeed'inbase'Vehicle'ofbase'Car'ofclass'MotorCycle'E:\-(2)\C++教學(xué)\教案\Text1.cpp(114):errorC2385:'MotorCycle::Weight'isambiguousE:\-(2)\C++教學(xué)\教案\Text1.cpp(114):warningC4385:couldbethe'Weight'inbase'Vehicle'ofbase'Bicycle'ofclass'MotorCycle'E:\-(2)\C++教學(xué)\教案\Text1.cpp(114):warningC4385:orthe'Weight'inbase'Vehicle'ofbase'Car'ofclass'MotorCycle'E:\-(2)\C++教學(xué)\教案\Text1.cpp(125):errorC2385:'MotorCycle::Run'isambiguousE:\-(2)\C++教學(xué)\教案\Text1.cpp(125):warningC4385:couldbethe'Run'inbase'Vehicle'ofbase'Bicycle'ofclass'MotorCycle'E:\-(2)\C++教學(xué)\教案\Text1.cpp(125):warningC4385:orthe'Run'inbase'Vehicle'ofbase'Car'ofclass'MotorCycle'E:\-(2)\C++教學(xué)\教案\Text1.cpp(126):errorC2385:'MotorCycle::Stop'isambiguousE:\-(2)\C++教學(xué)\教案\Text1.cpp(126):warningC4385:couldbethe'Stop'inbase'Vehicle'ofbase'Bicycle'ofclass'MotorCycle'E:\-(2)\C++教學(xué)\教案\Text1.cpp(126):warningC4385:orthe'Stop'inbase'Vehicle'ofbase'Car'ofclass'MotorCycle'執(zhí)行cl.exe時(shí)出錯(cuò).即輸出MaxSpeed、Weigh和調(diào)用函數(shù)Run（）和Stop（）函數(shù)時(shí)出現(xiàn)二義性問題。修改程序中重要是為數(shù)據(jù)組員和組員函數(shù)限定其所屬類即可。程序?yàn)椋篶lassMotorCycle:publicBicycle,publicCar//第3層類，從第2層兩個(gè)類公有繼承{public: MotorCycle(intm,intw,inth,ints):Bicycle(m,w,h),Car(m,w,s)//調(diào)用兩基類構(gòu)造函數(shù) { cout<<"ConstructingMotorCycle...\n"; } ~MotorCycle() { cout<<"DestructingMotorCycle...\n"; } voidShow()//輸出4個(gè)組員變量的信息，需消除二義性 { cout<<"It\'smaxspeedis:"<<Bicycle::MaxSpeed<<endl;//修改后 cout<<"It\'sweightis:"<<Car::Weight<<endl; //修改后 cout<<"It\'sheightis:"<<Height<<endl; cout<<"It\'sseatnumis:"<<SeatNum<<endl; }};intmain(){ MotorCyclemc(120,1000,2,2); //定義摩托車類對(duì)象 mc.Bicycle::Run(); //修改后 mc.Bicycle::Stop(); //修改后 mc.Show(); return0;}運(yùn)行成果：ConstructingVehicle...ConstructingBicycle...ConstructingVehicle...ConstructingCar...ConstructingMotorCycle...Thevehicleisrunning!Pleasestoprunning!It'smaxspeedis:120It'sweightis:1000It'sheightis:2It'sseatnumis:2DestructingMotorCycle...DestructingCar...DestructingVehicle...DestructingBycycle...DestructingVehicle...Pressanykeytocontinue⑤再將代碼恢復(fù)至上一步未修改前，即存在4個(gè)錯(cuò)誤、8個(gè)警告的狀態(tài)，再作一定的修改，將Vehicle申明為虛基類以消除二義性，同步修改第三層類的構(gòu)造函數(shù)，其他代碼不變，詳細(xì)請(qǐng)參照試驗(yàn)指導(dǎo)1的⑤。觀測(cè)運(yùn)行成果，理解此時(shí)構(gòu)造函數(shù)、析構(gòu)函數(shù)的調(diào)用次序及用虛基類消除二義性的原理。指導(dǎo)：將Vehicle申明為虛基類以消除二義性，詳細(xì)要在上面的基礎(chǔ)上修改如下地方。將classBicycle:publicVehicle修改為classBicycle:virtualpublicVehicle。將classCar:publicVehicle修改為classCar:virtualpublicVehicle。在第3層類的構(gòu)造函數(shù)MotorCycle(intm,intw,inth,ints):（16）的初始化列表中增長(zhǎng)對(duì)虛基類構(gòu)造函數(shù)的調(diào)用。本來注釋出錯(cuò)的地方將類名的限制去掉，恢復(fù)原樣。如： cout<<"It\'smaxspeedis:"<<Bicycle::MaxSpeed<<endl;//錯(cuò)誤恢復(fù)為：cout<<"It\'smaxspeedis:"<<MaxSpeed<<endl;按題意，將Vehicle申明為虛基類以消除二義性，詳細(xì)修改;將classBicycle:publicVehicle修改為classBicycle:virtualpublicVehicle。將classCar:publicVehicle修改為classCar:virtualpublicVehicle。程序修改為：classMotorCycle:publicBicycle,publicCar//第3層類，從第2層兩個(gè)類公有繼承{public: MotorCycle(intm,intw,inth,ints):Vehicle(m,w),Bicycle(m,w,h),Car(m,w,s)//調(diào)用兩基類構(gòu)造函數(shù) { cout<<"ConstructingMotorCycle...\n"; } ~MotorCycle() { cout<<"DestructingMotorCycle...\n"; } voidShow()//輸出4個(gè)組員變量的信息，需消除二義性 { cout<<"It\'smaxspeedis:"<<MaxSpeed<<endl;//對(duì)的 cout<<"It\'sweightis:"<<Weight<<endl; //對(duì)的 cout<<"It\'sheightis:"<<Height<<endl; cout<<"It\'sseatnumis:"<<SeatNum<<endl; }};intmain(){ MotorCyclemc(120,1000,2,2); //定義摩托車類對(duì)象 mc.Run(); //對(duì)的 mc.Stop();//對(duì)的 mc.Show(); return0;}運(yùn)行成果為：ConstructingVehicle...ConstructingBicycle...ConstructingCar...ConstructingMotorCycle...Thevehicleisrunning!Pleasestoprunning!It'smaxspeedis:120It'sweightis:1000It'sheightis:2It'sseatnumis:2DestructingMotorCycle...DestructingCar...DestructingBycycle...DestructingVehicle...Pressanykeytocontinue題目2：定義Base類及它的公有派生類Derived類，兩個(gè)類中均定義帶參數(shù)的構(gòu)造函數(shù)，基類中定義函數(shù)Show()，派生類中也定義一種同名的Show()，兩者輸出內(nèi)容有所區(qū)別。主函數(shù)中定義基類的對(duì)象、指針、引用，也定義派生類的對(duì)象。（①中6個(gè)空各0.3分，②分析0.2分）①對(duì)賦值兼容的4種狀況作測(cè)試，對(duì)每行的輸出成果進(jìn)行觀測(cè)，理解賦值兼容何時(shí)調(diào)用基類的組員函數(shù)，什么狀況下才會(huì)調(diào)用派生類的組員函數(shù)。②在主函數(shù)的return0;語句前增長(zhǎng)4條語句，觀測(cè)并記下編譯時(shí)的報(bào)錯(cuò)信息，理解賦值兼容的不可逆性。程序如下：#include<iostream>usingnamespacestd;classBase{ public: inti; Base(intx):i(x) { } voidshow() { cout<<"iinBaseis:"<<i<<endl; }};classDerived:publicBase{public: Derived(intx):Base(x) {} voidshow() { cout<<"iinDerivedis:"<<i<<endl; }};intmain(){ Baseb1(1); //定義基類對(duì)象b1 cout<<"基類對(duì)象b1.show():\n"; b1.show(); Derivedd1(2); //定義派生類對(duì)象d1 b1=d1; //用派生類對(duì)象給基類對(duì)象賦值 cout<<"基類b1=d1,b1.show():\n"; b1.show(); cout<<"派生類對(duì)象d1.show():\n"; d1.show(); Base&b2=d1; //用派生類對(duì)象來初始化基類引用 cout<<"引用b2=d1,b2.show():\n"; b2.show(); Base*b3=&d1; //派生類對(duì)象的地址賦給指向基類的指針 cout<<"基類指針b3=&d1,b3->show():\n"; b3->show(); Derived*d4=newDerived(3); //定義派生類指針并生成新對(duì)象 Base*b4=d4; //派生類指針賦給指向基類的指針 cout<<"基類指針b4=d4,b4->show():\n"; b4->show(); cout<<"派生類指針d4,d4->show():\n"; d4->show(); deleted4; return0;}運(yùn)行成果：基類對(duì)象b1.show():iinBaseis:1基類b1=d1,b1.show():iinBaseis:2派生類對(duì)象d1.show():iinDerivedis:2引用b2=d1,b2.show():iinBaseis:2基類指針b3=&d1,b3->show():iinBaseis:2基類指針b4=d4,b4->show():iinBaseis:3派生類指針d4,d4->show():iinDerivedis:3Pressanykeytocontinue對(duì)賦值兼容的4種狀況作測(cè)試，對(duì)每行的輸出成果進(jìn)行觀測(cè)，理解賦值兼容何時(shí)調(diào)用基類的組員函數(shù)，什么狀況下才會(huì)調(diào)用派生類的組員函數(shù)。答：4種狀況：基類對(duì)象=公有派生類對(duì)象b1=d1;b1.show();調(diào)用的是基類Base的組員函數(shù)show；指向基類對(duì)象的指針=公有派生類對(duì)象的地址Base*b3=&d1; b3->show();調(diào)用的是基類Base的組員函數(shù)show；指向基類對(duì)象的指針=指向公有派生類對(duì)象的指針Base*b4=d4;b4->show();調(diào)用的是基類Base的組員函數(shù)show；基類的引用=公有派生類對(duì)象，即派生類對(duì)象可以初始化基類的引用。Base&b2=d1;b2.show();調(diào)用的是基類Base的組員函數(shù)show；由此可知，只要是基類的對(duì)象或?qū)ο笾羔槪ㄒ茫┚{(diào)用的是基類的函數(shù)；只有在調(diào)用函數(shù)的對(duì)象或指針是派生類的時(shí)候才會(huì)調(diào)用派生類的組員函數(shù)。如d1.show();d4->show();均調(diào)用的是派生類的組員函數(shù)。在主函數(shù)的return0