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目录

 

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本章小结

        C++扩展了C语言的函数功能。通过将inline关键字用于函数定义，并在首次调用该函数前提供其函数定义，可以使得C++编译器将该函数视为内联函数。也就是说，编译器不是让程序跳到独立的代码段，以执行函数，而是用相应的代码替换函数调用。只有在函数很短时才能采用内联方式。         引用变量是一种伪装指针，它允许为变量创建别名（另一个名称）。引用变量主要被用作处理结构和类对象的函数的参数。通常，被声明为特定类型引用的标识符只能指向这种类型的数据；然而，如果一个类是从另一个类派生派生出来的，则基类引用可以指向派生类对象。        C++原型让您能够定义参数的默认值。如果函数调用省略了相应的参数，则程序将使用默认值；如果函数调用提供了参数值，则程序将使用这个值（而不是默认值）。只能在参数列表中从右到左提供默认参数。因此，如果为某个参数提供了默认值，则必须为该参数右边所有的参数提供默认值。        函数的特征是其参数列表。程序员可以定义两个同名函数，只要其特征标不同。这被称为函数多态或函数重载，通常，通过重载函数来为不同的数据类型提供相同的服务。        函数模板自动完成重载函数的过程。只需使用泛型和具体算法来定义函数，编译器将为程序中使用的特定参数类型生成正确的函数定义。

 

程序清单

 

8.1  内联函数

//inline.cpp -- using an inline function#include "stdafx.h"#include
   
    //inline double function definitioninline double square(double x){	return x * x;}int main(){	using namespace std;	double a, b;	double c = 13.0;	a = square(5.0);	b = square(4.5 + 7.5);	cout << "a = " << a << " , b = " << b << "\n";	cout << "c = " << c;	cout << ", c squared = " << square(c++) << "\n";	cout << "Now c = " << c << "\n";    return 0;}
   

8.2  创建引用变量

//firstref.cpp -- defining and using a reference#include "stdafx.h"#include
   
    int main(){	using namespace std;	int rats = 101;	int & rodents = rats;//rodents is a reference	cout << "rats = " << rats;	cout << ", rodents = " << rodents << endl;	rodents++;	cout << "rats = " << rats;	cout << ", rodents = " << rodents << endl;	//some implementations require type casting the following addresses to type unsigned	cout << "rats address = " << &rats;	cout << ", rodents address = " << &rodents << endl;	return 0;}
   

8.3  引用变量

//secref.cpp -- defining and using a reference#include "stdafx.h"#include
   
    int main(){	using namespace std;	int rats = 101;	int & rodents = rats;	cout << "rats = " << rats << ", rodents = " << rodents << endl;	cout << "rats address = " << &rats << ", rodents address = " << &rodents << endl;	int bunnies = 50;	rodents = bunnies;	cout << "bunnies = " << bunnies << ", rats = " << rats << "rodents = " << rodents << endl;	cout << "bunnies address = " << &bunnies << ", rodents address = " << &rodents << endl;	return 0;}
   

8.4  引用作为函数参数

//swaps.cpp -- swapping with reference and with pointers#include "stdafx.h"#include
   
    void swapr(int & a, int & b);//a,b are aliases for intsvoid swapp(int * p, int * q);//p,q are addresses of intsvoid swapv(int a, int b);//a,b are new variablesint main(){	using namespace std;	int wallet1 = 300;	int wallet2 = 350;	cout << "wallet1 = $" << wallet1;	cout << " wallet2 = $" << wallet2 << endl;	cout << "Using references to swap contents:\n";	swapr(wallet1, wallet2); //pass variables 	cout << "wallet1 = $" << wallet1; 	cout << " wallet2 = $" << wallet2 << endl;	cout << "Using pointers to swap contents:\n";	swapp(& wallet1, & wallet2); //pass addresses of variables	cout << "wallet1 = $" << wallet1;	cout << " wallet2 = $" << wallet2 << endl;	cout << "Trying to use passing by value:\n";	swapv(wallet1, wallet2); //pass values of variables	cout << "wallet1 = $" << wallet1;	cout << " wallet2 = $" << wallet2 << endl;	return 0;} void swapr(int & a, int & b) //use references{	int temp;	temp = a; //use a, b for values of variables	a = b;	b = temp;}void swapp(int * p, int * q) //use pointers{	int temp;	temp = *p; //use *p,*q for values of variables	*p = *q;	*q = temp;}void swapv(int a, int b) //try using values{	int temp;	temp = a;//use a,b for values of variables	a = b;	b = temp;}
   

8.5  引用参数的特点

//cubes.cpp -- regular and reference arguments#include "stdafx.h"#include
   
    double cube(double a);double refcube(double &ra);int main(){	using namespace std;	double x = 3.0;	cout << cube(x);	cout << " = cube of " << x << endl;	cout << refcube(x);	cout << " = cube of " << x << endl;	return 0;}double cube(double a){	a *= a * a;	return a;}double refcube(double &ra){	ra *= ra * ra;	return ra;}
   

8.6   结构引用作为函数参数

//strc_ref.cpp -- using structure references#include "stdafx.h"#include
   
    #include
    
     using namespace std;struct free_throws{	string name;	int made;	int attempts;	float percent;};void display(const free_throws & ft);void set_pc(free_throws & ft);free_throws & accumulate(free_throws & target, const free_throws & source);int main(){    //partial initialization - remaining members set to 0	free_throws one = { "Ifelsa Branch",13,14 };	free_throws two = { "Andor Knott",  10,16 };	free_throws three = { "Minnie Max",   7, 9 };	free_throws four = { "Whily Looper", 5, 9 };	free_throws five = { "Long Long",    6, 14 };	free_throws team = { "Throwgoods",   0, 0 };	//no initialization	free_throws dup;	set_pc(one);	display(one);	accumulate(team, one);	display(team);	//use return value as argument	display(accumulate(team, two));	accumulate(accumulate(team, three), four);	display(team);	//use return value in assignment	dup = accumulate(team, five);	cout << "Displaying team:\n";	display(team);	cout << "Displaying dup after assignment:\n";	display(dup);	set_pc(four);	//ill-advised assignment	accumulate(dup, five) = four;	cout << "Displaying dup afer ill-advise assignment:\n";	display(dup);	return 0;}void display(const free_throws & ft){	cout << "Name: " << ft.name << endl;	cout << " Made: " << ft.made << '\t';	cout << "Attempts: " << ft.attempts << '\t';	cout << "Percent: " << ft.percent << endl;}void set_pc(free_throws & ft){	if (ft.attempts != 0)		ft.percent = 100.0f*float(ft.made) / float(ft.attempts);	else		ft.percent = 0;}free_throws & accumulate(free_throws & target, const free_throws & source){	target.attempts += source.attempts;	target.made += source.made;	set_pc(target);	return target;}
    
   

8.7  程序崩溃

8.8  对象 继承和引用

//filefunc.cpp -- function with ostream &parameter#include "stdafx.h"#include
   
    #include
    
     #include
     
      using namespace std;void file_it(ostream &os, double fo, const double fe[], int n);const int LIMIT = 5;int main(){	ofstream fout;	const char *fn = "ep-data.txt";	fout.open(fn);	if (!fout.is_open())	{		cout << "Can't open " << fn << ". Bye.\n";		exit(EXIT_FAILURE);	}	double objective;	cout << "Enter the focal length of your telescope objective in mm: ";	cin >> objective;	double eps[LIMIT];	cout << "Enter the focal lengths,in mm,of " << LIMIT << " eyepieces:\n";	for (int i = 0; i < LIMIT; i++)	{		cout << "Eyepiece #" << i + 1 << ": ";		cin >> eps[i];	}	file_it(fout, objective, eps, LIMIT);	file_it(cout, objective, eps, LIMIT);	cout << "Done\n";	return 0;}void file_it(ostream &os, double fo, const double fe[], int n){	ios::fmtflags initial;	initial = os.setf(ios_base::fixed);//save initial formatting state	os.precision(0);	os << "Focal length of objective: " << fo << " mm\n";	os.setf(ios::showpoint);	os.precision(1);	os.width(12);	os << "f.1. eyepiece";	os.width(15);	os << "magnification" << endl;	for (int i = 0; i < n; i++)	{		os.width(12);		os << fe[i];		os.width(15);		os << int(fo / fe[i] + 0.5) << endl;	}	os.setf(initial);//restore initial formatting state}
     
    
   

8.9  默认参数

//left.cpp -- string function with a default argument#include "stdafx.h"#include
   
    const int ArSize = 80;char * left(const char*str, int n = 1);int main(){	using namespace std;	char sample[ArSize];	cout << "Enter a string:\n";	cin.get(sample, ArSize);	char *ps = left(sample, 4);	cout << ps << endl;	delete[] ps;	ps = left(sample);	cout << ps << endl;	delete[] ps;	return 0;}//This function returns a pointer to a new string consisting of the first n characters in the str string.char * left(const char*str, int n){	if (n < 0)		n = 0;	char *p = new char[n + 1];	int i;	for (i = 0; i < n && str[i]; i++)		p[i] = str[i];//copy characters	while (i <= n)		p[i++] = '\0';	return p;}
   

8.10  函数重载

//leftover.cpp -- overloading the left() function#include "stdafx.h"#include
   
    unsigned long left(unsigned long num, unsigned ct);char * left(const char * str, int n = 1);int main(){	using namespace std;	const char * trip = "Hawaii!!";	unsigned long n = 12345678;	int i = 1;	char* temp;	for ( i = 1; i < 10; i++)	{		cout << left(n, i) << endl;		temp = left(trip, i);		cout << temp << endl;		delete[] temp;//point to temporary storage	}	return 0;}//This function returns the first ct digits of the number num.unsigned long left(unsigned long num, unsigned ct){	unsigned digits = 1;	unsigned long n = num;	if (ct == 0 || num == 0)		return 0;	while (n /= 10)		digits++;	if (digits > ct)	{		ct = digits - ct;		while (ct--)			num /= 10;		return num;	}	else		return num;}//This function returns a pointer to a new string consisting of the first n characters in the str stringchar * left(const char * str, int n){	if (n < 0)		n = 0;	char *p = new char[n + 1];	int i;	for (i = 0; i < n&&str[i]; i++)		p[i] = str[i];//copy characters	while (i <= n)		p[i++] = '\0';//set rest of string to '\0'	return p;}
   

8.11  函数模板

//funtemp.cpp -- using a function template#include "stdafx.h"#include
   
    //function template prototypetemplate
    
     //or class Tvoid Swap(T &a, T &b);int main(){	using namespace std;	int i = 10;	int j = 20;	cout << "i = " << i << ", j = " << j << ".\n";	cout << "Using compiler-generated int swapper:\n";	Swap(i, j);//generates void Swap(int &, int &)	cout << "Now i = " << i << ", j = " << j << ".\n";	double x = 24.5;	double y = 81.7;	cout << "x, = " << x << ", y =" << y << ".\n";	cout << "Using compiler-generated double swapper:\n";	Swap(x, y);//generates void Swap(double &, double &)	cout << "Now x = " << x << ", y = " << y << ".\n";	return 0;}//function template definitiontemplate 
     
      void Swap(T &a, T &b){	T temp;//temp a variable of type T	temp = a;	a = b;	b = temp;}
     
    
   

8.12  重载的模板

//twotemps.cpp -- using overloaded template functions#include "stdafx.h"#include
   
    template
    
     void Swap(T &a, T &b);template
     
      void Swap(T *a, T *b, int n);void Show(int a[]);const int Lim = 8;int main(){	using namespace std;	int i = 10, j = 20;	cout << "i = " << i << ", j = " << j << ".\n";	cout << "Using compiler-generated int swapper:\n";	Swap(i, j);	cout << "Now i = " << i << ", j = " << j << ".\n";	int d1[Lim] = { 0,7,0,4,1,7,7,6 };	int d2[Lim] = { 0,7,2,0,1,9,6,9 };	cout << "Original arrays: \n";	Show(d1);	Show(d2);	Swap(d1, d2, Lim);	cout << "Sawpped arrays:\n";	Show(d1);	Show(d2);	return 0;}template
      
       void Swap(T &a, T &b){	T temp;	temp = a;	a = b;	b = temp;}template
       
        void Swap(T a[], T b[], int n){	T temp;	for (int i = 0; i < n; i++)	{		temp = a[i];		a[i] = b[i];		b[i] = temp;	}}void Show(int a[]){	using namespace std;	cout << a[0] << a[1] << "/" << a[2] << a[3] << "/";	for (int i = 4; i < Lim; i++)		cout << a[i];	cout << endl;}
       
      
     
    
   

8.13  显式具体化

// twoswap.cpp -- specialization overrides a template#include "stdafx.h"#include
   
    template 
    
     void Swap(T &a, T &b);struct job{	char name[40];	double salary;	int floor;};// explicit specialization 显式具体化template<> void Swap
     
      (job & j1, job & j2);void Show(job & j);int main(){	using namespace std;	cout.precision(2);	cout.setf(ios::fixed, ios::floatfield);	int i = 10, j = 20;	cout << "i = " << i << ", j = " << j << ".\n";	cout << "Using compiler-generated int swapper: \n";	Swap(i, j); // generates void Swap(int &, int &)	cout << "Now i = " << i << ", j = " << j << ".\n";	job sue = { "Susan Yaffee", 73000.60, 7 };	job sidney = { "Sidney Taffee", 78060.72, 9 };	cout << "Before job swapping: \n";	Show(sue);	Show(sidney);	Swap(sue, sidney); // uses void Swap(job & , job &)	cout << "After job swapping: \n";	Show(sue);	Show(sidney);	return 0;}template 
      
       void Swap(T &a, T &b) // general version{	T temp;	temp = a;	a = b;	b = temp;}// swaps just the salary and floor fields of a job structuretemplate<> void Swap
       
        (job &j1, job &j2) // specialization{	double t1;	int t2;	t1 = j1.salary;	j1.salary = j2.salary;	j2.salary = t1;	t2 = j1.floor;	j1.floor = j2.floor;	j2.floor = t2;}void Show(job & j){	using namespace std;	cout << j.name << ": $" << j.salary << " on floor " << j.floor << endl;}
       
      
     
    
   

8.14  部分排序规则

//tempover.cpp -- template overloading#include "stdafx.h"#include
   
    struct debts{	char name[50];	double amount;};template 
    
     void ShowArray(T arr[], int n);template 
     
      void ShowArray(T * arr[], int n);int main(){	using namespace std;	int things[6] = { 13,31,103,301,310,130 };	struct debts mr_E[3]	{		{"Ima Wolfe",2400.0},		{"Ura Foxe",1300.0},		{"Iby Stout",1800.0}	};	double * pd[3];	//set pointers to the amount members of the structures in mr_E	for (int i = 0; i < 3; i++)		pd[i] = &mr_E[i].amount;	cout << "Listing Mr.E's counts of things:\n";	//things is an array of int	ShowArray(things, 6);	cout << endl << "Listing Mr.E's debts:\n";	//pd is an array of pointers to double	ShowArray(pd, 3);//uses template B (more specialized)	return 0;}template 
      
       void ShowArray(T arr[], int n){	using namespace std;	cout << "template A\n";	for (int i = 0; i < n; i++)		cout << arr[i] << ' ';	cout << endl;}template 
       
        void ShowArray(T * arr[], int n){	using namespace std;	cout << "template B\n";	for (int i = 0; i < n; i++)		cout << *arr[i] << ' ';	cout << endl;}
       
      
     
    
   

8.15  自己选择

//choices.cpp -- choosing a template#include "stdafx.h"#include
   
    template
    
     T lesser(T a, T b){	return a < b ? a : b;}int lesser(int a, int b){	a = a < 0 ? -a : a;	b = b < 0 ? -b : b;	return a < b ? a : b;}int main(){	using namespace std;	int m = 20;	int n = -30;	double x = 15.5;	double y = 25.9;	cout << lesser(m, n) << endl;	cout << lesser(x, y) << endl;	cout << lesser<>(m, n) << endl;	cout << lesser
     
      (x, y) << endl;	return 0;}
     
    
   

 

课后编程习题答案

 

//practice.cpp //运行时删除或注释掉多余的部分#include "stdafx.h"#include
   
    #include
    
     #include
     
      #include
      
       //practice-1void show(const char * ps, int n = 0);int main(){	using namespace std;	char * pstr = "Hello\n";	show(pstr);	int num;	cout << "Enter a number: ";	cin >> num;	show(pstr, num);	cout << "Done\n";	return 0;} void show(const char * ps, int n){	using namespace std;	int lim = n;	if (n == 0)		lim = 1;	for (int i = 0; i < lim; i++)		cout << ps;}//practice-2using namespace std;struct CandyBar {	string brand;	double weight;	int calories;};void function(CandyBar &, char * str = "Millennium Munch", double a = 2.85, int b = 350);void show(const CandyBar &);int main(){	CandyBar x;	cout << "Please enter the brand: \n";	getline(cin, x.brand);	cout << "Please enter the weight: \n";	cin >> x.weight;	cout << "Please enter the colories: \n";	cin >> x.calories;	show(x);	function(x);	show(x);	return 0;} void show(const CandyBar &a){	cout << endl << a.brand << endl		<< a.weight << endl		<< a.calories << endl;} void function(CandyBar &r, char * str, double a, int b){	r.brand = str;	r.weight = a;	r.calories = b;}//practice-3using namespace std;void upper(string &);int main(){	string str;	cout << "Enter a string (q to quit): ";	getline(cin, str);	while (str != "q" && str != "Q")	{		upper(str);		cout << str << endl;		cout << "Next string (q to quit): ";		getline(cin, str);	} 	cout << "Bye.\n";	return 0;} void upper(string & a){	for (int i = 0; i < a.size(); i++)	{		if (islower(a[i]))			a[i] = toupper(a[i]);	}}//practice-4using namespace std;struct stringy {	char * str;	int ct;};void set(stringy &, char[]);void show(const stringy &, int n = 1);void show(const char[], int n = 1);int main(){	stringy beany;	char testing[] = "Reality isn't what it used to be.";	set(beany, testing);	show(beany);	show(beany, 2);	testing[0] = 'D';	testing[1] = 'u';	show(testing);	show(testing, 3);	show("Done!");	return 0;}void set(stringy & a, char b[]){	a.str = b;}void show(const stringy &x, int n){	for (int i = n; i > 0; i--)		cout << x.str << endl;}void show(const char a[], int n){	for (int i = n; i > 0; i--)		cout << a << endl;}//practice-5using namespace std;const int Num = 5;template 
       
        AnyType max5(AnyType[]);int main(){	int a[Num] = { 1, 2, 3, 4, 5 };	double b[Num] = { 1.1, 2.2, 3.3, 4.4, 5.5 };	int maxi = max5(a);	double maxd = max5(b);	cout << "max in a[5]: " << maxi << endl		<< "max in b[5]: " << maxd << endl;	return 0;}template 
        
         AnyType max5(AnyType ar[]){ AnyType max = ar[0]; for (int i = 0; i < 5; i++) { if (max < ar[i]) max = ar[i]; } return max;}//practice-6using namespace std;template 
         
          T maxn(T[], int);template <> const char* maxn
          
           (const char *[], int);int main(){ int a[6] = { 1, 2, 3, 4, 5, 6 }; double b[4] = { 1.1, 2.2, 3.3, 4.4 }; int maxi = maxn(a, 6); double maxd = maxn(b, 4); const char * c[5] = { "a", "bb", "ccc", "ddddd", "eeee" }; cout << "maxi: " << maxi << endl << "maxd: " << maxd << endl << "The max string of array is: " << maxn(c, 5) << endl; return 0;}template 
           
            T maxn(T ar[], int n){ T max = ar[0]; for (int i = 0; i < n; i++) { if (max < ar[i]) max = ar[i]; } return max;}template <> const char* maxn
            
             (const char * ar[], int n){ const char * maxs = ar[0]; for (int i = 1; i < n; i++) { if(strlen(maxs) < strlen(ar[i])) maxs = ar[i]; } return maxs;}//practice-7template 
             
              T SumArrray(T arr[], int n);template 
              
               T SumArrray(T * arr[], int n);struct debts{ char name[50]; double amount;};int main(){ using namespace std; int things[6] = { 13, 31, 103, 301, 310, 130 }; struct debts mr_E[3] = { { "Ima Wolfe", 2400.0 }, { "Ura Foxe", 1300.0 }, { "Iby Stout", 1800.0 } }; double * pd[3]; for (int i = 0; i < 3; i++) pd[i] = &mr_E[i].amount; cout << "Sum: Mr.E's counts of things: " << SumArrray(things, 6) << endl; cout << "Sum: Mr.E's debts: " << SumArrray(pd, 3) << endl; return 0;}template 
               
                T SumArrray(T arr[], int n){ using namespace std; T sum = 0; cout << "template A\n"; for (int i = 0; i < n; i++) sum += arr[i]; return sum;}template 
                
                 T SumArrray(T * arr[], int n){ using namespace std; T sum = 0; cout << "template B\n"; for (int i = 0; i < n; i++) sum += *arr[i]; return sum;}
                
               
              
             
            
           
          
         
        
       
      
     
    
   

 

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