编程练习
1.对Tv和Remote类做如下修改：
a. 让它们互为友元；
b.在Remote类中添加一个状态变量成员，该成员描述遥控器是出于常规模式还是互动模式；
c.在Remote中添加一个显示模式的方法；
d.在Tv类中添加一个对Remote中新成员进行切换的方法，该方法应当仅次于TV处于打开状态下才能运行。
编写一个小程序来测试这些新特性。
TV.h
// tv.h -- Tv and Remote classes
#ifndef TV_H_
#define TV_H_
class Remote;
class Tv
{
public:
friend class Remote; // Remote can access Tv private parts
enum {Off, On};
enum {MinVal,MaxVal = 20};
enum {Antenna, Cable};
enum {TV, DVD};
Tv(int s = Off, int mc = 125) : state(s), volume(5),
maxchannel(mc), channel(2), mode(Cable), input(TV) {}
void onoff() {state = (state == On)? Off : On;}
bool ison() const {return state == On;}
bool volup();
bool voldown();
void chanup();
void chandown();
void set_mode() {mode = (mode == Antenna)? Cable : Antenna;}
void set_input() {input = (input == TV)? DVD : TV;}
void settings() const; // display all settings
void shift_mode(Remote &r) const;
private:
int state; // on or off
int volume; // assumed to be digitized
int maxchannel; // maximum number of channels
int channel; // current channel setting
int mode; // broadcast or cable
int input; // TV or DVD
};
class Remote
{
private:
int mode; // controls TV or DVD
bool mode_status; // false:normal,true:interaction
public:
friend class Tv;
Remote(int m = Tv::TV) : mode(m),mode_status(false) {}
void show_status() const;
bool volup(Tv & t) { return t.volup();}
bool voldown(Tv & t) { return t.voldown();}
void onoff(Tv & t) { t.onoff(); }
void chanup(Tv & t) {t.chanup();}
void chandown(Tv & t) {t.chandown();}
void set_chan(Tv & t, int c) {t.channel = c;}
void set_mode(Tv & t) {t.set_mode();}
void set_input(Tv & t) {t.set_input();}
};
#endif
TV.cpp
// tv.cpp -- methods for the Tv class (Remote methods are inline)
#include
#include "TV.h"
bool Tv::volup()
{
if (volume < MaxVal)
{
volume++;
return true;
}
else
return false;
}
bool Tv::voldown()
{
if (volume > MinVal)
{
volume--;
return true;
}
else
return false;
}
void Tv::chanup()
{
if (channel < maxchannel)
channel++;
else
channel = 1;
}
void Tv::chandown()
{
if (channel > 1)
channel--;
else
channel = maxchannel;
}
void Tv::settings() const
{
using std::cout;
using std::endl;
cout << "TV is " << (state == Off? "Off" : "On") << endl;
if (state == On)
{
cout << "Volume setting = " << volume << endl;
cout << "Channel setting = " << channel << endl;
cout << "Mode = "
<< (mode == Antenna? "antenna" : "cable") << endl;
cout << "Input = "
<< (input == TV? "TV" : "DVD") << endl;
}
}
void Tv::shift_mode(Remote &r) const{
if (state == 1)
if (r.mode_status)
r.mode_status = false;
else
r.mode_status = true;
else std::cout << "TV is off" << std::endl;
}
void Remote::show_status() const{
if (mode_status)
std::cout << "Remote mode status: interaction"
<< std::endl;
else
std::cout << "Remote mode status: normal"
<< std::endl;
}
main.cpp
#include
#include "TV.h"
int main()
{
using std::cout;
Tv s42;
cout << "Initial settings for 42\" TV:\n";
s42.settings();
s42.onoff();
s42.chanup();
cout << "\nAdjusted settings for 42\" TV:\n";
s42.settings();
Remote grey;
grey.show_status();
grey.set_chan(s42, 10);
grey.volup(s42);
grey.volup(s42);
cout << "\n42\" settings after using remote:\n";
s42.settings();
s42.shift_mode(grey);
grey.show_status();
Tv s58(Tv::On);
s58.set_mode();
grey.set_chan(s58,28);
cout << "\n58\" settings:\n";
s58.settings();
// std::cin.get();
return 0;
}
2.修改程序清单15.11，使两种异常类型都是从头文件提供的logic_error类派生出的类。让每个what()方法都报告函数名和问题的性质。异常对象不用存储错误的参数值，而只需支持what()方法。
exc_mean.h
// exc_mean.h -- exception classes for hmean(), gmean()
#include
#include
using namespace std;
class bad_hmean : public invalid_argument
{
public:
bad_hmean() : invalid_argument("a + b = 0") {}
};
class bad_gmean : public range_error
{
public:
bad_gmean() : range_error("a < 0, b < 0") {}
};
error4.cpp
#ifndef ERROR_EXC_MEAN_H
#define ERROR_EXC_MEAN_H
#include "exc_mean.h"
#include
#include // or math.h, unix users may need -lm flag
// function prototypes
using namespace std;
double hmean(double a, double b);
double gmean(double a, double b);
int main()
{
double x, y, z;
cout << "Enter two numbers: ";
while (cin >> x >> y)
{
try { // start of try block
z = hmean(x,y);
cout << "Harmonic mean of " << x << " and " << y
<< " is " << z << endl;
cout << "Geometric mean of " << x << " and " << y
<< " is " << gmean(x,y) << endl;
cout << "Enter next set of numbers : ";
}// end of try block
catch (bad_hmean &gh) // start of catch block
{
cout << "Caught the error!" << endl;
cout << gh.what() << endl;
cout << "Try again.\n";
continue;
}
catch (bad_gmean &bg)
{
cout << "Caught the error!" << endl;
cout << bg.what() << endl;
// cout << "Values used: " << hg.v1 << ", "
// << hg.v2 << endl;
cout << "Sorry, you don't get to play any more.\n";
break;
} // end of catch block
}
cout << "Bye!\n";
return 0;
}
double hmean(double a, double b)
{
if (a == -b)
throw bad_hmean();
return 2.0 * a * b / (a + b);
}
double gmean(double a, double b)
{
if (a < 0 || b < 0)
throw bad_gmean();
return std::sqrt(a * b);
}
#endif //ERROR_EXC_MEAN_H
3.这个练习与编程练习2相同，但异常类是从一个这样的基类派生而来的：它是从logic_error派生而来的，并存储两个参数值。异常类应该有一个这样的方法：报告这些值以函数名。程序使用一个catch块来捕获基类异常，其中任何一种从该基类异常派生而来的异常都将导致循环结束。
exc_mean.h
#include
#include
using namespace std;
class bad : public logic_error
{
private:
double v1,v2;
public:
bad(double v1,double v2) : v1(v1), v2(v2), logic_error("logic error!") {}
void show_error() { cout << "error value: " << v1 <<" "< error4.cpp
#ifndef ERROR_EXC_MEAN_H
#define ERROR_EXC_MEAN_H
#include "exc_mean.h"
#include
#include // or math.h, unix users may need -lm flag
// function prototypes
using namespace std;
double hmean(double a, double b);
double gmean(double a, double b);
int main()
{
double x, y, z;
cout << "Enter two numbers: ";
while (cin >> x >> y)
{
try { // start of try block
z = hmean(x,y);
cout << "Harmonic mean of " << x << " and " << y
<< " is " << z << endl;
cout << "Geometric mean of " << x << " and " << y
<< " is " << gmean(x,y) << endl;
cout << "Enter next set of numbers : ";
}// end of try block
catch (bad &gh) // start of catch block
{
cout << "Caught the error!" << endl;
cout << gh.what() << endl;
gh.show_error();
// cout << ".\n";
break;
}
}
cout << "Bye!\n";
return 0;
}
double hmean(double a, double b)
{
if (a == -b)
throw bad(a,b);
return 2.0 * a * b / (a + b);
}
double gmean(double a, double b)
{
if (a < 0 || b < 0)
throw bad(a,b);
return std::sqrt(a * b);
}
#endif //ERROR_EXC_MEAN_H
4.程序清单15.16在每个try后面都使用两个catch块，以确保nbad_index 异常导致方法 label_val() 被调用。请修改该程序，在每个try块后面只使用一个catch块，并使用RTTI来确保合适时调用 label_val()。
sales.h
#ifndef SALES_SALES_H
#define SALES_SALES_H
#include
#include
class Sales
{
public:
enum {MONTHS = 12}; // could be a static const
class bad_index : public std::logic_error
{
private:
int bi; // bad index value
public:
explicit bad_index(int ix,
const std::string & s = "Index error in Sales object\n");
int bi_val() const {return bi;}
virtual ~bad_index() throw() {}
};
explicit Sales(int yy = 0);
Sales(int yy, const double * gr, int n);
virtual ~Sales() { }
int Year() const { return year; }
virtual double operator[](int i) const;
virtual double & operator[](int i);
private:
double gross[MONTHS];
int year;
};
class LabeledSales : public Sales
{
public:
class nbad_index : public Sales::bad_index
{
private:
std::string lbl;
public:
nbad_index(const std::string & lb, int ix,
const std::string & s = "Index error in LabeledSales object\n");
const std::string & label_val() const {return lbl;}
virtual ~nbad_index() throw() {}
};
explicit LabeledSales(const std::string & lb = "none", int yy = 0);
LabeledSales(const std::string & lb, int yy, const double * gr, int n);
virtual ~LabeledSales() { }
const std::string & Label() const {return label;}
virtual double operator[](int i) const;
virtual double & operator[](int i);
private:
std::string label;
};
#endif //SALES_SALES_H
sales.cpp
#include "sales.h"using std::string;Sales::bad_index::bad_index(int ix, const string & s ) : std::logic_error(s), bi(ix){}Sales::Sales(int yy){ year = yy; for (int i = 0; i < MONTHS; ++i) gross[i] = 0;}Sales::Sales(int yy, const double * gr, int n){ year = yy; int lim = (n < MONTHS)? n : MONTHS; int i; for (i = 0; i < lim; ++i) gross[i] = gr[i]; // for i > n and i < MONTHS for ( ; i < MONTHS; ++i) gross[i] = 0;}double Sales::operator[](int i) const{ if(i < 0 || i >= MONTHS) throw bad_index(i); return gross[i];}double & Sales::operator[](int i){ if(i < 0 || i >= MONTHS) throw bad_index(i); return gross[i];}LabeledSales::nbad_index::nbad_index(const string & lb, int ix, const string & s ) : Sales::bad_index(ix, s){ lbl = lb;}LabeledSales::LabeledSales(const string & lb, int yy) : Sales(yy){ label = lb;}LabeledSales::LabeledSales(const string & lb, int yy, const double * gr, int n) : Sales(yy, gr, n){ label = lb;}double LabeledSales::operator[](int i) const{ if(i < 0 || i >= MONTHS) throw nbad_index(Label(), i); return Sales::operator[](i);}double & LabeledSales::operator[](int i){ if(i < 0 || i >= MONTHS) throw nbad_index(Label(), i); return Sales::operator[](i);}
main.cpp
#include #include "sales.h"int main(){ using std::cout; using std::cin; using std::endl; double vals1[12] = { 1220, 1100, 1122, 2212, 1232, 2334, 2884, 2393, 3302, 2922, 3002, 3544 }; double vals2[12] = { 12, 11, 22, 21, 32, 34, 28, 29, 33, 29, 32, 35 }; Sales sales1(2011, vals1, 12); LabeledSales sales2("Blogstar",2012, vals2, 12 ); cout << "First try block:\n"; try { int i; cout << "Year = " << sales1.Year() << endl; for (i = 0; i < 12; ++i) { cout << sales1[i] << ' '; if (i % 6 == 5) cout << endl; } cout << "Year = " << sales2.Year() << endl; cout << "Label = " << sales2.Label() << endl; for (i = 0; i <= 12; ++i) { cout << sales2[i] << ' '; if (i % 6 == 5) cout << endl; } cout << "End of try block 1.\n"; } catch(Sales::bad_index & bad) { cout << bad.what(); if (typeid(bad)== typeid(LabeledSales::nbad_index)) { cout << "Company: " << ((LabeledSales::nbad_index &)bad).label_val() << endl; cout << "bad index: " << bad.bi_val() << endl; } else { cout << "bad index: " << bad.bi_val() << endl; } } cout << "\nNext try block:\n"; try { sales2[2] = 37.5; sales1[20] = 23345; cout << "End of try block 2.\n"; } catch(Sales::bad_index & bad) { cout << bad.what(); if (typeid(bad)== typeid(LabeledSales::nbad_index)) { cout << "Company: " << ((LabeledSales::nbad_index &)bad).label_val() << endl; cout << "bad index: " << bad.bi_val() << endl; } else { cout << "bad index: " << bad.bi_val() << endl; } } cout << "done\n"; // std::cin.get(); return 0;}