C++ Primer Plus 第六版第十三章課後編程練習答案

首先，對於將題中基類修改爲虛函數版本，我們只需要將基類的公有函數部分除構造函數和友元之外的函數，聲明時前面加上關鍵字virtual即可；然後對於派生類，我們在私有成員裏面添加一個char數組，然後將繼承的函數寫出來即可。

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];//添加一組char成員，用於存儲指出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

//檢測文件按題目即可
#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();
}

練習1中，我們的成員變量的類型是使用的char數組，本題要求我們改爲動態內存分配，所以成員變量的類型我們可以選爲char指針，那麼這裏最最需要注意的就是，這樣改過之後，析構函數就必須要發揮作用了，析構函數內部就必須要把構造函數裏面初始化時動態分配的內存給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;//添加一組char成員，用於存儲指出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

接下來對於實現文件呢，一方面注意構造函數內部初始化時，都必須首先進行動態內存分配，然後纔可以進行strcpy_s函數的賦值，另一方面就是析構函數必須把構造函數裏面動態分配的內存都刪掉。其他內容不需要改變。

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];//注意構造函數內部初始化時，都必須首先進行動態內存分配，然後纔可以進行strcpy_s函數的賦值
    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;//析構函數必須把構造函數裏面動態分配的內存都刪掉
    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;
}

檢測文件不變，同上題。

本題要求在DMA類的基礎上進行修改，將三個類統一改爲從一個基類ABC派生而來。這裏要求使用ABC類指針數組並讓用戶決定創建的對象類型，即需要做一個交互；同時添加一個View方法用於數據顯示，並要求該方法爲虛函數。本來lacksDMA類和hasDMA類就是派生於baseDMA類的，所以我們只需使baseDMA類派生於ABC類即可，另外在每個類內部添加一個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;//題要求在類定義中添加virtual View()方法以處理數據顯示
};

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

對於實現文件，幾乎與書上的程序清單13.15相同，添加了View方法，在baseDMA類的View方法主要是顯示label和rating，而lacksDMA類的View方法新增顯示color，hasDMA類的View方法新增顯示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;
}

以下檢測文件裏，多次使用了cin.ignore()函數，這是因爲在每次cin之後，緩衝區內部都會多出一個回車符，導致後面cin.getline()函數執行時，還不等你輸入信息，就直接彈出了後面的信息，使用cin.ignore()函數可以有效解決這個問題。

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

//直接按題給
#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;
}

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