C++ Primer Plus 第六版第十三章课后编程练习答案

迷南。 2023-07-22 14:28 2阅读 0赞

首先，对于将题中基类修改为虚函数版本，我们只需要将基类的公有函数部分除构造函数和友元之外的函数，声明时前面加上关键字virtual即可；然后对于派生类，我们在私有成员里面添加一个char数组，然后将继承的函数写出来即可。

cd.h

#ifndef CD_H
    #define CD_H
    #include <iostream>
    using namespace std;
    class Cd{
        char performers[50];
        char label[20];
        int selections;
        double playtime;
    public:
        Cd(char * s1, char * s2, int n, double x);
        Cd(const Cd & d);
        Cd();
    
        virtual ~Cd();
        virtual void Report() const ;
        virtual Cd &operator=(const Cd & d);
    };
    
    class Classic : public Cd
    {
        char mainworks[50];//添加一组char成员，用于存储指出CD中主要作品的字符串
    public:
        Classic(char * s0, char * s1, char * s2, int n, double x);
        Classic(char * s0, Cd & rs);
        Classic();
        virtual ~Classic();
        virtual void Report() const ;
        virtual Classic &operator=(const Classic & d);
    };
    
    #endif

cd.cpp

#include "cd.h"
    #include <iostream>
    using namespace std;
    #include <cstring>
    
    Cd::Cd(char *s1, char *s2, int n, double x)
    {
        strcpy_s(performers, 50, s1);
        strcpy_s(label, 20, s2);
        selections = n;
        playtime = x;
    }
    
    Cd::Cd()
    {
        strcpy_s(performers, 50, "null");
        strcpy_s(label, 20, "null");
        selections = 0;
        playtime = 0;
    }
    
    Cd::~Cd()
    {}
    
    void Cd ::Report() const
    {
        cout << "In this CD disk, the performrs are " << performers << endl;
        cout << "The labels are " << label << endl;
        cout << "There are " << selections << " selections and lasts " << playtime << " minutes.\n";
    }
    
    Cd & Cd::operator=(const Cd & d)
    {
        strcpy_s(performers, 50, d.performers);
        strcpy_s(label, 20, d.label);
        selections = d.selections;
        playtime = d.playtime;
        return *this;
    }
    
    Classic::Classic(char *s0, char *s1, char *s2, int n, double x)
    : Cd(s1, s2, n, x)
    {
        strcpy_s(mainworks, 50, s0);
    }
    
    Classic::Classic(char *s0, Cd &rs)
    : Cd(rs)
    {
        strcpy_s(mainworks, 50, s0);
    }
    
    Classic::Classic()
    : Cd()
    {
        strcpy_s(mainworks, 50, "null");
    }
    
    Classic::~Classic()
    {}
    
    void Classic::Report() const
    {
        Cd::Report();
        cout << "The main works of this disk are " << mainworks << endl;
    }
    
    Classic & Classic::operator=(const Classic & d)
    {
        if(this == &d)
            return *this;
        Cd::operator=(d);
        strcpy_s(mainworks, 50, d.mainworks);
        return *this;
    }

play.cpp

//检测文件按题目即可
    #include <iostream>
    using namespace std;
    #include "cd.h"
    void Bravo(const Cd & disk);
    int main()
    {
        Cd c1("Beatles", "Capitol", 14, 35.5);
        Classic c2 = Classic("Piano Sonata in B flat, Fantasia in C",
                "Alfred Brendel", "Philips", 2, 57.17);
        Cd *pcd = &c1;
    
        cout << "Using object directly:\n";
        c1.Report();
        c2.Report();
    
        cout << "Using type cd * pointer to objects:\n";
        pcd->Report();
        pcd = &c2;
        pcd->Report();
    
        cout << "Calling a function with a Cd reference argument:\n";
        Bravo(c1);
        Bravo(c2);
    
        cout << "Testing assignment: ";
        Classic copy;
        copy = c2;
        copy.Report();
    
        return 0;
    }
    
    void Bravo(const Cd & disk)
    {
        disk.Report();
    }

练习1中，我们的成员变量的类型是使用的char数组，本题要求我们改为动态内存分配，所以成员变量的类型我们可以选为char指针，那么这里最最需要注意的就是，这样改过之后，析构函数就必须要发挥作用了，析构函数内部就必须要把构造函数里面初始化时动态分配的内存给delete掉。

cd.h

#ifndef CD_H
    #define CD_H
    #include <iostream>
    using namespace std;
    class Cd{
        char * performers;
        char * label;
        int selections;
        double playtime;
    public:
        Cd(char * s1, char * s2, int n, double x);
        Cd(const Cd & d);
        Cd();
    
        virtual ~Cd();
        virtual void Report() const ;
        virtual Cd &operator=(const Cd & d);
    };
    
    class Classic : public Cd
    {
        char * mainworks;//添加一组char成员，用于存储指出CD中主要作品的字符串
    public:
        Classic(char * s0, char * s1, char * s2, int n, double x);
        Classic(char * s0, Cd & rs);
        Classic();
        virtual ~Classic();
        virtual void Report() const ;
        virtual Classic &operator=(const Classic & d);
    };
    
    #endif

接下来对于实现文件呢，一方面注意构造函数内部初始化时，都必须首先进行动态内存分配，然后才可以进行strcpy\_s函数的赋值，另一方面就是析构函数必须把构造函数里面动态分配的内存都删掉。其他内容不需要改变。

cd.cpp

#include "cd.h"
    #include <iostream>
    using namespace std;
    #include <cstring>
    
    Cd::Cd(char *s1, char *s2, int n, double x)
    {
        performers = new char [strlen(s1) + 1];//注意构造函数内部初始化时，都必须首先进行动态内存分配，然后才可以进行strcpy_s函数的赋值
        strcpy_s(performers, strlen(s1) + 1, s1);
        label = new char [strlen(s2) + 1];
        strcpy_s(label, strlen(s2) + 1, s2);
        selections = n;
        playtime = x;
    }
    
    Cd::Cd()
    {
        performers = new char [5];
        strcpy_s(performers, 5, "null");
        label = new char [5];
        strcpy_s(label, 5, "null");
        selections = 0;
        playtime = 0;
    }
    
    Cd::~Cd()
    {
        delete [] performers;//析构函数必须把构造函数里面动态分配的内存都删掉
        delete [] label;
    }
    
    void Cd ::Report() const
    {
        cout << "In this CD disk, the performrs are " << performers << endl;
        cout << "The labels are " << label << endl;
        cout << "There are " << selections << " selections and lasts " << playtime << " minutes.\n";
    }
    
    Cd & Cd::operator=(const Cd & d)
    {
        performers = new char [strlen(d.performers) + 1];
        strcpy_s(performers, strlen(d.performers) + 1, d.performers);
        label = new char [strlen(d.label) + 1];
        strcpy_s(label, strlen(d.label) + 1, d.label);
        selections = d.selections;
        playtime = d.playtime;
        return *this;
    }
    
    Classic::Classic(char *s0, char *s1, char *s2, int n, double x)
    : Cd(s1, s2, n, x)
    {
        mainworks = new char [strlen(s0) + 1];
        strcpy_s(mainworks, strlen(s0) + 1, s0);
    }
    
    Classic::Classic(char *s0, Cd &rs)
    : Cd(rs)
    {
        mainworks = new char [strlen(s0) + 1];
        strcpy_s(mainworks, strlen(s0) + 1, s0);
    }
    
    Classic::Classic()
    : Cd()
    {
        mainworks = new char [5];
        strcpy_s(mainworks, 5, "null");
    }
    
    Classic::~Classic()
    {
        delete [] mainworks;
    }
    
    void Classic::Report() const
    {
        Cd::Report();
        cout << "The main works of this disk are " << mainworks << endl;
    }
    
    Classic & Classic::operator=(const Classic & d)
    {
        if(this == &d)
            return *this;
        Cd::operator=(d);
        mainworks = new char [strlen(d.mainworks) + 1];
        strcpy_s(mainworks, strlen(d.mainworks) + 1, d.mainworks);
        return *this;
    }

检测文件不变，同上题。

本题要求在DMA类的基础上进行修改，将三个类统一改为从一个基类ABC派生而来。这里要求使用ABC类指针数组并让用户决定创建的对象类型，即需要做一个交互；同时添加一个View方法用于数据显示，并要求该方法为虚函数。本来lacksDMA类和hasDMA类就是派生于baseDMA类的，所以我们只需使baseDMA类派生于ABC类即可，另外在每个类内部添加一个View方法。

dma.h

#ifndef DMA_H
    #define DMA_H
    #include <iostream>
    using namespace std;
    
    class ABC{
    public:
        ABC();
        ~ABC();
        virtual void View() = 0;//题要求在类定义中添加virtual View()方法以处理数据显示
    };
    
    class baseDMA : public ABC
    {
        char * label;
        int rating;
    public:
        baseDMA(const char * l = "null", int r = 0);
        baseDMA(const baseDMA & rs);
        virtual ~baseDMA();
        baseDMA &operator=(const baseDMA & rs);
        friend ostream &operator<< (ostream & os, const baseDMA & rs);
        virtual void View();
    };
    
    class lacksDMA : public baseDMA
    {
        enum {COL_LEN = 40};
        char color[COL_LEN];
    public:
        lacksDMA(const char * c = "blank", const char * l = "null", int r = 0);
        lacksDMA(const char * c, const baseDMA & rs);
        friend ostream &operator<<(ostream & os, const lacksDMA & rs);
        virtual void View();
    };
    
    class hasDMA : public baseDMA
    {
        char * style;
    public:
        hasDMA(const char * s = "none", const char * l = "null", int r = 0);
        hasDMA(const char * s, const baseDMA & rs);
        hasDMA(const hasDMA & hs);
        ~hasDMA();
        hasDMA &operator=(const hasDMA & rs);
        friend ostream  &operator<< (ostream & os, const hasDMA & rs);
        virtual void View();
    };
    
    #endif

对于实现文件，几乎与书上的程序清单13.15相同，添加了View方法，在baseDMA类的View方法主要是显示label和rating，而lacksDMA类的View方法新增显示color，hasDMA类的View方法新增显示style。

dma.cpp

#include "dma.h"
    using namespace std;
    #include <iostream>
    #include <string>
    
    ABC::ABC()
    {}
    
    ABC::~ABC()
    {}
    
    baseDMA::baseDMA(const char * l, int r)
    {
        label = new char[strlen(l) + 1];
        strcpy_s(label, strlen(l) + 1, l);
        rating = r;
    }
    
    baseDMA::baseDMA(const baseDMA &rs)
    {
        label = new char [strlen(rs.label) + 1];
        strcpy_s(label, strlen(rs.label) + 1, rs.label);
        rating = rs.rating;
    }
    
    baseDMA::~baseDMA()
    {
        delete [] label;
    }
    
    baseDMA & baseDMA::operator=(const baseDMA & rs)
    {
        if(this == &rs)
            return *this;
        delete [] label;
        label = new char [strlen(rs.label) + 1];
        strcpy_s(label, strlen(rs.label) + 1, rs.label)
        rating = rs.rating;
        return *this;
    }
    
    ostream &operator<<(ostream & os, const baseDMA & rs)
    {
        os << "Label: " << rs.label << endl;
        os << "Rating: " << rs.rating << endl;
        return os;
    }
    
    void baseDMA::View()
    {
        cout << "Label: " << label << endl;
        cout << "Rating: " << rating << endl;
    }
    
    lacksDMA::lacksDMA(const char *c, const char *l, int r) : baseDMA(l ,r)
    {
        strncpy_s(color, 40, c, 39);
        color[39] = '\0';
    }
    
    lacksDMA::lacksDMA(const char *c, const baseDMA &rs) : baseDMA(rs)
    {
        strncpy_s(color, 40, c, COL_LEN - 1);
        color[COL_LEN - 1] = '\0';
    }
    
    ostream &operator<<(ostream & os, const lacksDMA & ls)
    {
        os << (const baseDMA &)ls;
        os << "Color: " << ls.color << endl;
        return os;
    }
    
    void lacksDMA::View()
    {
        baseDMA::View();
        cout << "Color: " << color << endl;
    }
    
    hasDMA::hasDMA(const char *s, const char *l, int r) : baseDMA(l, r)
    {
        style = new char [strlen(s) + 1];
        strcpy_s(style, strlen(s) + 1, s);
    }
    
    hasDMA::hasDMA(const char *s, const baseDMA &rs) : baseDMA(rs)
    {
        style = new char [strlen(s) + 1];
        strcpy_s(style, strlen(s) + 1, s);
    }
    
    hasDMA::hasDMA(const hasDMA &hs) : baseDMA(hs)
    {
        style = new char [strlen(hs.style) + 1];
        strcpy_s(style, strlen(hs.style) + 1, hs.style);
    }
    
    hasDMA::~hasDMA()
    {
        delete [] style;
    }
    
    hasDMA & hasDMA::operator=(const hasDMA & hs)
    {
        if(this == &hs)
            return *this;
        baseDMA::operator=(hs);
        delete [] style;
        style = new char[strlen(hs.style) + 1];
        strcpy_s(style, strlen(hs.style) + 1, hs.style);
        return *this;
    }
    
    ostream & operator<<(ostream & os, const hasDMA & hs)
    {
        os << (const baseDMA &)hs;
        os << "Style: " << hs.style << endl;
        return os;
    }
    
    void hasDMA::View()
    {
        baseDMA::View();
        cout << "Style: " << style << endl;
    }

以下检测文件里，多次使用了cin.ignore()函数，这是因为在每次cin之后，缓冲区内部都会多出一个回车符，导致后面cin.getline()函数执行时，还不等你输入信息，就直接弹出了后面的信息，使用cin.ignore()函数可以有效解决这个问题。

play.cpp

#include "dma.h"
    using namespace std;
    #include <iostream>
    
    int main()
    {
        baseDMA shirt("Portabelly", 8);
        lacksDMA balloon("red", "Blimpo", 4);
        hasDMA map("Mercator", "Buffalo Keys", 5);
        cout << "Displaying baseDMA object:\n";
        cout << shirt << endl;
        cout << "Displaying lackDMA object:\n";
        cout << balloon << endl;
        cout << "Displaying hasDMA object:\n";
        cout << map << endl;
        lacksDMA balloon2(balloon);
        cout << "Result of lackDMA copy:\n";
        cout << balloon2 << endl;
        hasDMA map2;
        map2 = map;
        cout << "Result of hasDMA assignment:\n";
        cout << map2 << endl;
        cout << endl << "Shirt:\n";
        shirt.View();
        cout << endl << "Balloon:\n";
        balloon.View();
        cout << endl << "Map:\n";
        map.View();
        cout << endl << "Balloon2:\n";
        balloon2.View();
        cout << endl << "Map2:\n";
        map2.View();
    
        cout << "\nHow many inputs: ";
        int number;
        cin >> number;
        cin.ignore();
        for(int i=0; i<number; i++)
        {
            cout << "\n Enter '1' for baseDMA, '2' for lackDMA, '3' for hasDMA: " ;
            char flag;
            while (cin >> flag&& (flag != '1' && flag != '2' && flag != '3'))
            {
                cin.ignore();
                cout << "Enter 1, 2, or 3: ";
            }
            cin.ignore();
            if(flag == '1')
            {
                char *label = new char[20] ;
                int rating;
                cout << "Enter label: ";
                cin.getline(label, 20);
                cout << "Enter rating: ";
                cin >> rating;
                baseDMA * base = new baseDMA(label, rating);
                cout << endl << "Input baseDMA: \n";
                base->View();
            }
            else if (flag == '2')
            {
                char *label = new char[20];
                int rating;
                char *color = new char[40];
                cout << "Enter label: ";
                cin.getline(label, 20);
                cout << "Enter rating: ";
                cin >> rating;
                cin.ignore();
                cout << "Enter color: ";
                cin.getline(color, 40);
                lacksDMA *lacks = new lacksDMA(color, label, rating);
                cout << endl << "Input lacksDMA: \n";
                lacks->View();
            }
            else if (flag == '3')
            {
                char *label = new char[20];
                int rating;
                char *style = new char[40];
                cout << "Enter label: ";
                cin.getline(label, 20);
                cout << "Enter rating: ";
                cin >> rating;
                cin.ignore();
                cout << "Enter style: ";
                cin.getline(style, 40);
                hasDMA *has = new hasDMA(style, label, rating);
                cout << endl << "Input hasDMA: \n";
                has->View();
            }
        }
    
        return 0;
    }

port.h

//直接按题给
    #ifndef PORT_H
    #define PORT_H
    #include <iostream>
    using namespace std;
    class Port
    {
        char * brand;
        char style[20];
        int bottles;
    public:
        Port(const char * br = "none", const char * st = "none", int b = 0);
        Port(const Port & p);
        virtual ~Port() {delete [] brand;}
        Port &operator = (const Port & p);
        Port &operator += (int b);
        Port &operator -= (int b);
        int BottleCount() const { return bottles;}
        virtual void Show() const ;
        friend ostream &operator<< (ostream & os, const Port & p);
    };
    
    class VintagePort : public Port
    {
        char * nickname;
        int year;
    public:
        VintagePort();
        VintagePort(const char * br, int b, const char * nn, int y);
        VintagePort(const VintagePort & vp);
        ~VintagePort() {delete [] nickname;}
        VintagePort &operator=(const VintagePort & vp);
        void Show() const ;
        friend ostream &operator<<(ostream & os, const VintagePort & vp);
    };
    
    #endif

port.cpp

#include <iostream>
    #include "port.h"
    using namespace std;
    #include <string>
    
    Port::Port(const char *br, const char *st, int b)
    {
        brand = new char [strlen(br) + 1];
        strcpy_s(brand, strlen(br) + 1, br);
        strcpy_s(style, 20, st);
        bottles = b;
    }
    
    Port::Port(const Port &p)
    {
        brand = new char [strlen(p.brand) + 1];
        strcpy_s(brand, strlen(p.brand) + 1, p.brand);
        strcpy_s(style, 20, p.style);
        bottles = p.bottles;
    }
    
    Port & Port::operator=(const Port & p)
    {
        brand = new char [strlen(p.brand) + 1];
        strcpy_s(brand, strlen(p.brand) + 1, p.brand);
        strcpy_s(style, 20, p.style);
        bottles = p.bottles;
        return *this;
    }
    
    Port & Port::operator+=(int b)
    {
        bottles += b;
        return *this;
    }
    
    Port & Port::operator-=(int b)
    {
        bottles -= b;
        return *this;
    }
    
    void Port::Show() const
    {
        cout << "Brand: " << brand << endl;
        cout << "Style: " << style << endl;
        cout << "Bottles: " << bottles << endl;
    }
    
    ostream& operator<<(ostream &os, const Port &p)
    {
        os << "Brand: " << p.brand << ", Style: " << p.style << ", Bottles: " << p.bottles << endl;
        return os;
    }
    
    VintagePort::VintagePort()
    {
        nickname = new char [5];
        strcpy_s(nickname, 5, "none");
        year = 0;
    }
    
    VintagePort::VintagePort(const char *br, int b, const char *nn, int y)
    {
        nickname = new char [strlen(nn) + 1];
        strcpy_s(nickname, strlen(nn) + 1, nn);
        year = y;
    }
    
    VintagePort::VintagePort(const VintagePort &vp)
    {
        nickname = new char [strlen(vp.nickname) + 1];
        strcpy_s(nickname, strlen(vp.nickname) + 1, vp.nickname);
        year = vp.year;
    }
    
    VintagePort & VintagePort::operator=(const VintagePort & vp)
    {
        nickname = new char [strlen(vp.nickname) + 1];
        strcpy_s(nickname, strlen(vp.nickname) + 1, vp.nickname);
        year = vp.year;
        return *this;
    }
    
    void VintagePort::Show() const
    {
        Port::Show();
        cout << "Nickname: " << nickname << endl;
        cout << "Year: " << year << endl;
    }
    
    ostream &operator<<(ostream & os, const VintagePort & vp)
    {
        os << (const Port&)vp;
        os << ", " << vp.nickname << ", " << vp.year;
        return os;
    }

play.cpp

#include "port.h"
    #include <iostream>
    using namespace std;
    #include <string>
    
    int main()
    {
        Port wine1("Leoardo", "white", 15);
        Port wine2 = wine1;
        cout << "Now your wines: \n";
        wine1.Show();
        wine2.Show();
        wine1+= 18;
        wine2 -= 6;
        cout << "After the change, your wine's bottles: \n";
        cout << "Wine1: ";
        wine1.BottleCount();
        cout << "Wine2: ";
        wine2.BottleCount();
        cout << "And conclusion: \n";
        cout << wine1 << endl;
        cout << wine2 << endl;
        cout << endl;
        cout << "Now your wines upgrade to VintagePort class.\n";
        VintagePort wine3("Elma", 21, "tww", 23);
        VintagePort wine4;
        (Port &)wine4 = (Port &)wine3;
        (VintagePort &)wine4 = (VintagePort &)wine3;
        cout << "Now the new wines are:\n";
        wine3.Show();
        wine4.Show();
        wine3 += 17;
        wine4 -= 5;
        cout << "After the change, new wines' bottles:\n";
        cout << "Wine3: ";
        wine3.BottleCount();
        cout << "Wine4: ";
        wine4.BottleCount();
        cout << "Conclusion: \n";
        cout << wine3 << endl;
        cout << wine4 << endl;
        cout << endl;
    
        return 0;
    }