C ++ Primer Plus 第六版 第十三章编程练习答案
1.以下面的类声明为基础：
// base class
class Cd { //represents a CD disk
private:
char performers[50];
char label[20];
int selections; //number of selections
double playtime; //playing time in minute
public:
Cd(char * s1, char * s2, int n, double x);
Cd(const Cd & d);
Cd();
~Cd();
void Report() const; //reports all CD data
Cd & operator=(const Cd & d);
};
派生出一个Classic类，并添加一组char成员，用于存储指出CD中主要作品的字符串。修改上述声明，使基类的搜有函数都是虚的。如果上述定义声明的某个方法并不需要，则请删除它。使用下面的程序测试您的产品：
#include
using namespace std;
#include"classic.h" //which will contain #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(); //use Cd method
c2.Report(); //use Classic method
cout<<"Using type cd *pointer to objects:\n";
pcd->Report(); //use Cd method for cd object
pcd = &c2;
pcd->Report(); //use Classic method for classic object
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();
2.完成练习1，但让两个类使用动态内存分配而不是长度固定的数组来记录字符串。
// base class
class Cd { //represents a CD disk
private:
char performers[50];
char label[20];
int selections; //number of selections
double playtime; //playing time in minute
public:
Cd(char * s1, char * s2, int n, double x);
Cd(const Cd & d);
Cd();
~Cd();
void Report() const; //reports all CD data
Cd & operator=(const Cd & d);
};
派生出一个Classic类，并添加一组char成员，用于存储指出CD中主要作品的字符串。修改上述声明，使基类的搜有函数都是虚的。如果上述定义声明的某个方法并不需要，则请删除它。使用下面的程序测试您的产品：
#include
using namespace std;
#include"classic.h" //which will contain #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(); //use Cd method
c2.Report(); //use Classic method
cout<<"Using type cd *pointer to objects:\n";
pcd->Report(); //use Cd method for cd object
pcd = &c2;
pcd->Report(); //use Classic method for classic object
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();
}
//cd.h
#ifndef CD_H_INCLUDED
#define CD_H_INCLUDED
class Cd
{
private:
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
{
private:
char opus[100];
public:
Classic();
Classic ( const Classic & c );
Classic ( char * o, char *s1, char *s2, int n, double x );
~Classic();
virtual void Report() const;
virtual Cd & operator= ( const Classic & c );
};
#endif // CD_H_INCLUDED
//cd.cpp
#include
#include
#include"cd.h"
using std::strcpy;
using std::cout;
using std::cin;
using std::endl;
Cd::Cd ( char *s1, char *s2, int n, double x )
{
strcpy ( performers, s1 );
strcpy ( label, s2 );
selections = n;
playtime = x;
}
Cd::Cd ( const Cd & d )
{
strcpy ( performers, d.performers );
strcpy ( label, d.label );
selections = d.selections;
playtime = d.playtime;
}
Cd::Cd()
{
strcpy ( performers, "NULL" );
strcpy ( label, "NULL" );
selections = 0;
playtime = 0;
}
Cd::~Cd() {}
void Cd::Report() const
{
cout << "performers: " << performers << endl;
cout << "label: " << label << endl;
cout << "selections: " << selections << endl;
cout << "playtime: " << playtime << endl;
}
Cd & Cd::operator= ( const Cd & d )
{
strcpy ( performers, d.performers );
strcpy ( label, d.label );
selections = d.selections;
playtime = d.playtime;
return *this;
}
Classic::Classic() : Cd()
{
strcpy ( opus, "NULL" );
}
Classic::Classic ( const Classic & c ) : Cd ( c )
{
strcpy ( opus, c.opus );
}
Classic::Classic ( char * o, char *s1, char *s2, int n, double x ) : Cd ( s1, s2, n, x )
{
strcpy ( opus, o );
}
Classic::~Classic() {}
void Classic::Report() const
{
Cd::Report();
cout << "opus: " << opus << endl;
}
Cd & Classic::operator= ( const Classic & c )
{
if ( this == &c )
return *this;
Cd::operator= ( c );
strcpy ( opus, c.opus );
return *this;
}
//main.cpp
#include
#include"cd.cpp"
#include"cd.h"
void Bravo ( const Cd& disk );
int main()
{
using namespace std;
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(); //use Cd method
cout << endl;
c2.Report(); //use Classic method
cout << endl;
cout << "Using type cd *pointer to objects:\n";
pcd->Report(); //use Cd method for cd object
cout << endl;
pcd = &c2;
pcd->Report(); //use Classic method for classic object
cout << endl;
cout << "Calling a function with a Cd reference argument:\n";
Bravo ( c1 );
cout << endl;
Bravo ( c2 );
cout << endl;
cout << "Testing assignment: ";
Classic copy;
copy = c2;
copy.Report();
cout << endl;
system ( "pause" );
return 0;
}
void Bravo ( const Cd& disk )
{
disk.Report();
}
2.完成练习1，但让两个类使用动态内存分配而不是长度固定的数组来记录字符串。
#ifndef CD_H_INCLUDED
#define CD_H_INCLUDED
class Cd
{
private:
char *performers;
char *label;
int selections;
double playtime;
public:
Cd ( const char *s1, const 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
{
private:
char *opus;
public:
Classic();
Classic ( const Classic & c );
Classic ( const char * o, const char *s1, const char *s2, int n, double x );
~Classic();
virtual void Report() const;
virtual Cd & operator= ( const Classic & c );
};
#endif // CD_H_INCLUDED
#include
#include
#include"cd.h"
using std::strcpy;
using std::strlen;
using std::cout;
using std::cin;
using std::endl;
Cd::Cd ( const char *s1, const char *s2, int n, double x )
{
performers=new char[strlen(s1)+1];
label=new char[strlen(s2)+1];
strcpy ( performers, s1 );
strcpy ( label, s2 );
selections = n;
playtime = x;
}
Cd::Cd ( const Cd & d )
{
performers=new char[strlen(d.performers)+1];
label=new char[strlen(d.label)+1];
strcpy ( performers, d.performers );
strcpy ( label, d.label );
selections = d.selections;
playtime = d.playtime;
}
Cd::Cd()
{
performers=new char[1];
label=new char[1];
performers[0]='\0';
label[0]='\0';
selections = 0;
playtime = 0;
}
Cd::~Cd()
{
delete []performers;
delete []label;
}
void Cd::Report() const
{
cout << "performers: " << performers << endl;
cout << "label: " << label << endl;
cout << "selections: " << selections << endl;
cout << "playtime: " << playtime << endl;
}
Cd & Cd::operator= ( const Cd & d )
{
if ( this == &d )
return *this;
delete []performers;
delete []label;
performers=new char[strlen(d.performers)+1];
label=new char[strlen(d.label)+1];
strcpy ( performers, d.performers );
strcpy ( label, d.label );
selections = d.selections;
playtime = d.playtime;
return *this;
}
Classic::Classic() : Cd()
{
opus=new char[1];
opus[0]='\0';
}
Classic::Classic ( const Classic & c ) : Cd ( c )
{
opus=new char[strlen(c.opus)+1];
strcpy ( opus, c.opus );
}
Classic::Classic (const char * o,const char *s1, const char *s2, int n, double x ) : Cd ( s1, s2, n, x )
{
opus=new char[strlen(o)+1];
strcpy ( opus, o );
}
Classic::~Classic()
{
delete []opus;
}
void Classic::Report() const
{
Cd::Report();
cout << "opus: " << opus << endl;
}
Cd & Classic::operator= ( const Classic & c )
{
if ( this == &c )
return *this;
Cd::operator= ( c );
delete []opus;
opus=new char[strlen(c.opus)+1];
strcpy ( opus, c.opus );
return *this;
}
4.Benevolent Order of Programmers用来维护瓶装葡萄酒箱。为描述它，BOP Portmaster设置了一个Port类，并声明如下：
#include
using namespace std;
class Port
{
private:
char * brand;
char style[20]; //i.e., tawny, ruby, vintage
int bottles;
public:
Port(const char * br= "none", const char *st = "none", int b =0);
Port(const Port & p); //copy constructor
virtual ~Port() { delete [] brand; }
Port & operator=(const Port&p);
Port & operator+=(int b); //add b to bottles
Port & operator-=(int b); //subtracts b from bottles , if available
int BottleCount() const {return bottles; ]
virtual void Show() const;
friend ostream & operator<<(ostream & os, const Port &p);
};
show()方法按下面的格式显示信息：
Brand: Gallo
Kind: tawny
Bottles: 20
operator<<()函数按下面的格式显示信息（末尾没有换行符）：
Gallo, tawny, 20
PortMaster完成了Port类的方法定义后派生了VintagePort类，然后被解职——因为不小心将一瓶45度Cockburn泼到了正在准备烤肉调料的人身上，VintagePort类如下显示：
class VintagePort: public Port //style necessarily = "vintage"
{
private:
char * nickname; //i.e. , "The Noble" or "Old Velvet", etc.
int year; //vintage year
public:
VintagePort();
VintagePort(const char * br, const char *st, int b, const char * nn, int y);
//注：我认为上面这个构造函数少了一个st字符串，这个字符串是用于给style字符串赋值的
VintagePort(const VintagePort & vp);
~VintagePort() { delete [] nickname; }
VintagePort & operator = (const VintagePort & vp);
void show() const;
friend ostream & operator <<(ostream & os, const VintagePort &vp);
};
您被制定指定负责完成VintagePort。
a。第一个任务是重新创建Port方法定义，因为前任被开除时销毁了方法定义。
b。第二个任务是解释为什么有的方法重新定义了，而有些没有重新定义。
c。第三个任务解释为何没有将operator=() 和operator<<()声明为虚的。
d。第四个任务是提供VintagePort中各个方法的定义。
答：
②对于基类的虚函数，有必要重新定义；
③因为赋值运算符和友元函数不能被继承；
#ifndef PORT_H_INCLUDED
#define PORT_H_INCLUDED
#include
using std::cout;
using std::ostream;
class Port
{
private:
char * brand;
char style[20]; //i.e., tawny, ruby, vintage
int bottles;
public:
Port(const char * br = "none", const char *st = "none", int b = 0);
Port(const Port & p); //cpoy constructor
virtual ~Port() { delete[] brand; }
Port & operator=(const Port&p);
Port & operator+=(int b); //add b to bottles
Port & operator-=(int b); //subtracts b from bottles , if available
int BottleCount() const { return bottles; }
virtual void Show() const;
friend ostream & operator<<(ostream & os, const Port &p);
};
class VintagePort : public Port //style necessarily = "vintage"
{
private:
char * nickname; //i.e. , "The Noble" or "Old Velvet", etc.
int year; //vintage year
public:
VintagePort();
VintagePort(const char * br, const char *st, int b, const char * nn, int y);
VintagePort(const VintagePort & vp);
~VintagePort() { delete[] nickname; }
VintagePort & operator = (const VintagePort & vp);
virtual void Show() const;
friend ostream & operator <<(ostream & os, const VintagePort &vp);
};
#endif // PORT_H_INCLUDED
#include
#include
#include"port.h"
using namespace std;
Port::Port ( const char * br, const char *st, int b )
{
int len = strlen ( br );
brand = new char[len + 1];
strcpy ( brand, br );
strcpy ( style, st );
bottles = b;
}
Port::Port ( const Port & p )
{
int len = strlen ( p.brand );
brand = new char[len + 1];
strcpy ( brand, p.brand );
strcpy ( style, p.style );
bottles = p.bottles;
}
Port & Port::operator= ( const Port & p )
{
delete [] brand;
int len = strlen ( p.brand );
brand = new char[len + 1];
strcpy ( brand, p.brand );
strcpy ( style, 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 << "Kind: " << style << endl;
cout << "Bottles: " << bottles << endl;
}
ostream & operator<< ( ostream & os, const Port & p )
{
os << p.brand << ", " << p.style << ", " << p.bottles;
return os;
}
VintagePort::VintagePort() : Port()
{
nickname = new char[1];
nickname[0] = '\0';
year = 0;
}
VintagePort::VintagePort ( const char * br, const char *st, int b, const char * nn, int y ) : Port ( br, st, b )
{
int len = strlen ( nn );
nickname = new char[len + 1];
strcpy ( nickname, nn );
year=y;
}
VintagePort::VintagePort ( const VintagePort & vp ) : Port ( vp )
{
int len = strlen ( vp.nickname );
nickname = new char[len + 1];
strcpy ( nickname, vp.nickname );
year = vp.year;
}
VintagePort & VintagePort::operator = ( const VintagePort & vp )
{
if ( this == &vp )
return *this;
Port::operator= ( vp );
delete []nickname;
int len = strlen ( vp.nickname );
nickname = new char[len + 1];
strcpy ( nickname, 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 )
{
operator<<(cout,( const Port & ) vp);
//os << ( const Port & ) vp;
os << ", " << vp.nickname << ", " << vp.year;
return os;
}