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C++ Primer Plus（第六版）第8章 函数探幽

ppt视频教程下载 • 2022-12-17 • 随笔 • 阅读 82

C++ Primer Plus（第六版）第8章 函数探幽,第1张

C++ Primer Plus（第六版）第8章 函数探幽 inline.cpp 
// inline.cpp -- using an inline function
#include 

// an inline function definition
inline 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);   // can pass expressions
	cout << "a = " << a << ", b = " << b << "n";
	cout << "c = " << c;
	cout << ", c squared = " << square(c++) << "n";
	cout << "Now c = " << c << "n";
	// cin.get();
	return 0;
}

执行结果：

a = 25, b = 144
c = 13, c squared = 169
Now c = 14
 firstref.cpp 
// firstref.cpp -- defining and using a reference
#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;
    // cin.get();
    return 0; 
}

执行结果：

rats = 101, rodents = 101
rats = 102, rodents = 102
rats address = 00CFF9C4, rodents address = 00CFF9C4
 secref.cpp 
// secref.cpp -- defining and using a reference
#include 
int main()
{
	using namespace std;
	int rats = 101;
	int & rodents = rats;   // rodents is a reference

	cout << "rats = " << rats;
	cout << ", rodents = " << rodents << endl;

	cout << "rats address = " << &rats;
	cout << ", rodents address = " << &rodents << endl;

	int bunnies = 50;
	rodents = bunnies;       // can we change the reference?
	cout << "bunnies = " << bunnies;
	cout << ", rats = " << rats;
	cout << ", rodents = " << rodents << endl;

	cout << "bunnies address = " << &bunnies;
	cout << ", rodents address = " << &rodents << endl;
	// cin.get();
	return 0;
}

执行结果：

rats = 101, rodents = 101
rats address = 00CFFDB4, rodents address = 00CFFDB4
bunnies = 50, rats = 50, rodents = 50
bunnies address = 00CFFD9C, rodents address = 00CFFDB4
swaps.cpp  
// swaps.cpp -- swapping with references and with pointers
#include 
void swapr(int & a, int & b);   // a, b are aliases for ints
void swapp(int * p, int * q);   // p, q are addresses of ints
void swapv(int a, int b);       // a, b are new variables
int 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 again: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;
	// cin.get();
	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;
}

 执行效果：
 

wallet1 = 0 wallet2 = 0
Using references to swap contents:
wallet1 = 0 wallet2 = 0
Using pointers to swap contents again:
wallet1 = 0 wallet2 = 0
Trying to use passing by value:
wallet1 = 0 wallet2 = 0
cubes.cpp  
// cubes.cpp -- regular and reference arguments
#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;
	// cin.get();
	return 0;
}

double cube(double a)
{
	a *= a * a;
	return a;
}

double refcube(double &ra)
{
	ra *= ra * ra;
	return ra;
}

执行结果： 

27 = cube of 3
27 = cube of 27
 strc_ref.cpp 
//strc_ref.cpp -- using structure references
#include 
#include 
struct free_throws
{
	std::string name;
	int made;
	int attempts;
	float percent;
};//free_throws结构

void display(const free_throws & ft);
void set_pc(free_throws & ft);
free_throws & accumulate(free_throws &target, const free_throws &source);

int main()
{
	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 };
	free_throws dup;
	set_pc(one);
	display(one);//调用display函数 
	//Name: Ifelsa Branch    Made: 13      Attempts : 14    Percent : 92.8571
	display(team);//Name: Throwgoods
    //Made: 0       Attempts : 0     Percent : 0
	// use return value as argument
	display(accumulate(team, two));//调用display函数 
    //Name: Throwgoods
	//Made : 10      Attempts : 16    Percent : 62.5
	accumulate(accumulate(team, three), four);//其中22=10+7+5 34=16+9+9 
	//这里调用accumulate函数和前面的two累加到一起
	display(team);//Name: Throwgoods
    //Made: 22      Attempts : 34    Percent : 64.7059 

	// use return value in assignment
	dup = accumulate(team, five);//22+6(five)=28 34+14(five)=48
	std::cout << "Displaying team:n";
	display(team);//Name: Throwgoods
    //Made: 28      Attempts : 48    Percent : 58.3333
	std::cout << "Displaying dup after assignment:n";
	display(dup);//Name: Throwgoods
    //Made: 28      Attempts : 48    Percent : 58.3333
	set_pc(four);
	// ill-advised assignment
	accumulate(dup, five) = four;//首先将five的数据添加到dup中，再将four的内容覆盖dup的内容
	std::cout << "Displaying dup after ill-advised assignment:n";
	display(dup);//Name: Whily Looper
    //Made: 5       Attempts : 9     Percent : 55.5556
	// std::cin.get();
	return 0;
}

void display(const free_throws & ft)
{
	using std::cout;
	cout << "Name: " << ft.name << 'n';
	cout << "  Made: " << ft.made << 't';
	cout << "Attempts: " << ft.attempts << 't';
	cout << "Percent: " << ft.percent << 'n';
}
void set_pc(free_throws & ft)
{
	if (ft.attempts != 0)
		ft.percent = 100.0f *float(ft.made) / float(ft.attempts);//相当于100*13/14=92.85714285
	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;
}

执行结果：

Name: Ifelsa Branch
  Made: 13      Attempts: 14    Percent: 92.8571
Name: Throwgoods
  Made: 0       Attempts: 0     Percent: 0
Name: Throwgoods
  Made: 10      Attempts: 16    Percent: 62.5
Name: Throwgoods
  Made: 22      Attempts: 34    Percent: 64.7059
Displaying team:
Name: Throwgoods
  Made: 28      Attempts: 48    Percent: 58.3333
Displaying dup after assignment:
Name: Throwgoods
  Made: 28      Attempts: 48    Percent: 58.3333
Displaying dup after ill-advised assignment:
Name: Whily Looper
  Made: 5       Attempts: 9     Percent: 55.5556
 strquote.cpp   
// strquote.cpp  -- different designs
#include 
#include 
using namespace std;
string version1(const string & s1, const string & s2);
const string & version2(string & s1, const string & s2);  // has side effect
const string & version3(string & s1, const string & s2);  // bad design

int main()
{
	string input;
	string copy;
	string result;

	cout << "Enter a string: ";
	getline(cin, input);
	copy = input;
	cout << "Your string as entered: " << input << endl;
	result = version1(input, "***");
	cout << "Your string enhanced: " << result << endl;
	cout << "Your original string: " << input << endl;

	result = version2(input, "###");
	cout << "Your string enhanced: " << result << endl;
	cout << "Your original string: " << input << endl;

	cout << "Resetting original string.n";
	input = copy;
	result = version3(input, "@@@");//执行错误，程序试图引用已经释放的内存
	cout << "Your string enhanced: " << result << endl;
	cout << "Your original string: " << input << endl;
	// cin.get();
	// cin.get();
	return 0;
}

string version1(const string & s1, const string & s2)
{
	string temp;

	temp = s2 + s1 + s2;
	return temp;
}

const string & version2(string & s1, const string & s2)   // has side effect
{
	s1 = s2 + s1 + s2;
	// safe to return reference passed to function
	return s1;
}

const string & version3(string & s1, const string & s2)   // bad design
{
	string temp;

	temp = s2 + s1 + s2;
	// unsafe to return reference to local variable
	return temp;
}

执行结果：

Enter a string: It is my fault.
Your string as entered: It is my fault.
Your string enhanced: ***It is my fault.***
Your original string: It is my fault.
Your string enhanced: ###It is my fault.###
Your original string: ###It is my fault.###
Resetting original string.
filefunc.cpp   
//filefunc.cpp -- function with ostream & parameter
#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;//输入1800
	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);//将目镜数据写入到文件ep-data.txt中
	file_it(cout, objective, eps, LIMIT);//将目镜数据打印到屏幕上
	cout << "Donen";
	// cin.get();
	// cin.get();
	return 0;
}

void file_it(ostream & os, double fo, const double fe[], int n)
{
	// save initial formatting state
	ios_base::fmtflags initial;
	initial = os.setf(ios_base::fixed, ios_base::floatfield);
	std::streamsize sz = os.precision(0);
	os << "Focal length of objective: " << fo << " mmn";
	os.precision(1);
	os.width(12);
	os << "f.l. eyepiece";
	os.width(15);
	os << "magnification" << endl;//f.l. eyepiece  magnification
	//30.0             60    30*60=1800(objective)
    //19.0             95     19*95=1805(objective)
	//14.0            129      14*129=1806(objective)
	//8.8            205       8.8*205=1806(objective)
	//7.5            240       7.5*240=1800(objective)
	for (int i = 0; i < n; i++)
	{
		os.width(12);
		os << fe[i];
		os.width(15);
		os << int(fo / fe[i] + 0.5) << endl;
	}
	// restore initial formatting state
	os.setf(initial, ios_base::floatfield);
	os.precision(sz);
}

 执行结果：

Enter the focal length of your telescope objective in mm: 1800
Enter the focal lengths, in mm, of 5 eyepieces:
Eyepiece #1: 30
Eyepiece #2: 19
Eyepiece #3: 14
Eyepiece #4: 8.8
Eyepiece #5: 7.5
Focal length of objective: 1800 mm
f.l. eyepiece  magnification
        30.0             60
        19.0             95
        14.0            129
         8.8            205
         7.5            240
Done
left.cpp  
// left.cpp -- string function with a default argument
#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);//调用left函数 取前四个元素
	cout << ps << endl;
	delete[] ps;       // free old string
	ps = left(sample);//取第一个元素
	cout << ps << endl;
	delete[] ps;       // free new string
	// cin.get();
	// cin.get();
	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++] = '';  // set rest of string to ''
	return p;
}

执行效果：

Enter a string:
forthcoming
fort
f
leftover.cpp  
// leftover.cpp -- overloading the left() function
#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!!";   // test value 源代码在这里有错误
	//需要加上const 否则会报错
	unsigned long n = 12345678; // test value
	int i;
	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
	}
	// cin.get();
	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;       // return 0 if no digits
	while (n /= 10)//12345678/10=1234567
		digits++;//2
	if (digits > ct)
	{
		ct = digits - ct;
		while (ct--)
			num /= 10;//1234567/10=123456
		return num;         // return left ct digits 123456
	}
	else                // if ct >= number of digits
		return num;     // return the whole number
}

// 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++] = '';  // set rest of string to ''
	return p;
}

执行结果：

1
H
12
Ha
123
Haw
1234
Hawa
12345
Hawai
123456
Hawaii
1234567
Hawaii!
12345678
Hawaii!!
12345678
Hawaii!!
 funtemp.cpp 
// funtemp.cpp -- using a function template
#include 
// function template prototype
template   // or class T
void Swap(T &a, T &b);

int main()
{
	using namespace std;
	int i = 10;
	int j = 20;
	cout << "i, j = " << i << ", " << j << ".n";
	cout << "Using compiler-generated int swapper:n";
	Swap(i, j);  // generates void Swap(int &, int &)
	cout << "Now i, j = " << i << ", " << j << ".n";

	double x = 24.5;
	double y = 81.7;
	cout << "x, y = " << x << ", " << y << ".n";
	cout << "Using compiler-generated double swapper:n";
	Swap(x, y);  // generates void Swap(double &, double &)
	cout << "Now x, y = " << x << ", " << y << ".n";
	// cin.get();
	return 0;
}

// function template definition
template   // or class T
void Swap(T &a, T &b)
{
	T temp;   // temp a variable of type T
	temp = a;
	a = b;
	b = temp;
}

 执行结果：

i, j = 10, 20.
Using compiler-generated int swapper:
Now i, j = 20, 10.
x, y = 24.5, 81.7.
Using compiler-generated double swapper:
Now x, y = 81.7, 24.5.
 twotemps.cpp 
// twotemps.cpp -- using overloaded template functions
#include 
template      // original template
void Swap(T &a, T &b);

template      // new 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, j = " << i << ", " << j << ".n";
	cout << "Using compiler-generated int swapper:n";
	Swap(i, j);              // matches original template
	cout << "Now i, j = " << i << ", " << 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);//07/04/1776
	Show(d2);//07/20/1969
	Swap(d1, d2, Lim);        // matches new template
	cout << "Swapped arrays:n";
	Show(d1);//07/20/1969
	Show(d2);//07/04/1776
	// cin.get();
	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[0]=0 a[1]=7
	cout << a[2] << a[3] << "/";//a[2]=0 a[3]=4
	for (int i = 4; i < Lim; i++)
		cout << a[i];//输出a[4]至a[7]
	cout << endl;
}

执行结果：

i, j = 10, 20.
Using compiler-generated int swapper:
Now i, j = 20, 10.
Original arrays:
07/04/1776
07/20/1969
Swapped arrays:
07/20/1969
07/04/1776
 twoswap.cpp 
// twoswap.cpp -- specialization overrides a template
#include 
template 
void Swap(T &a, T &b);

struct job
{
    char name[40];
    double salary;
    int floor;
};

// explicit specialization 
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, j = " << i << ", " << j << ".n";
    cout << "Using compiler-generated int swapper:n";
    Swap(i,j);    // generates void Swap(int &, int &)
    cout << "Now i, j = " << i << ", " << j << ".n";

    job sue = {"Susan Yaffee", 73000.60, 7};//struct job
	//char name[40];
	//double salary;
	//int floor;
    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);
    // cin.get();
    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 structure

template <> void Swap(job &j1, job &j2)  // specialization
{
    double t1;
    int t2;
    t1 = j1.salary;
    j1.salary = j2.salary;
    j2.salary = t1;//交换salary
    t2 = j1.floor;
    j1.floor = j2.floor;
    j2.floor = t2;//交换floor
}

void Show(job &j)
{
    using namespace std;
    cout << j.name << ": $" << j.salary
         << " on floor " << j.floor << endl;
}

 执行结果：

i, j = 10, 20.
Using compiler-generated int swapper:
Now i, j = 20, 10.
Original arrays:
07/04/1776
07/20/1969
Swapped arrays:
07/20/1969
07/04/1776
 tempover.cpp 
// tempover.cpp --- template overloading
#include 

template             // template A
void ShowArray(T arr[], int n);

template             // template B
void ShowArray(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];

	// 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);  // uses template A
	cout << "Listing Mr. E's debts:n";
	// pd is an array of pointers to double
	ShowArray(pd, 3);      // uses template B (more specialized)
	// cin.get();
	return 0;
}

template 
void ShowArray(T arr[], int n)
{
	using namespace std;
	cout << "template An";
	for (int i = 0; i < n; i++)
		cout << arr[i] << ' ';
	cout << endl;
}

template 
void ShowArray(T * arr[], int n)
{
	using namespace std;
	cout << "template Bn";
	for (int i = 0; i < n; i++)
		cout << *arr[i] << ' ';
	cout << endl;
}

执行结果：

Listing Mr. E's counts of things:
template A
13 31 103 301 310 130
Listing Mr. E's debts:
template B
2400 1300 1800

 删去template B后，得到的结果是： 

// tempover.cpp --- template overloading
#include 

template             // template A
void ShowArray(T arr[], int n);

//template             // template B
//void ShowArray(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];

	// 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);  // uses template A
	cout << "Listing Mr. E's debts:n";
	// pd is an array of pointers to double
	ShowArray(pd, 3);      // uses template B (more specialized)
	// cin.get();
	return 0;
}

template 
void ShowArray(T arr[], int n)
{
	using namespace std;
	cout << "template An";
	for (int i = 0; i < n; i++)
		cout << arr[i] << ' ';
	cout << endl;
}

//template 
//void ShowArray(T * arr[], int n)
//{
//	using namespace std;
//	cout << "template Bn";
//	for (int i = 0; i < n; i++)
//		cout << *arr[i] << ' ';
//	cout << endl;
//}

执行结果：

Listing Mr. E's counts of things:
template A
13 31 103 301 310 130
Listing Mr. E's debts:
template A
0093F75C 0093F79C 0093F7DC
 choices.cpp 
// choices.cpp -- choosing a template
#include 

template
T lesser(T a, T b)         // #1
{
	return a < b ? a : b;
}

int lesser(int a, int b)  // #2
{
	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;       // use #2 
	//该函数调用与模板函数和非模板函数都匹配，所以选择非模板函数
	cout << lesser(x, y) << endl;       // use #1 with double
	//函数调用与模板匹配(T为double)
	cout << lesser<>(m, n) << endl;     // use #1 with int
	//lesser<>(m, n)中<>指出，编译器一个选择模板匹配函数，而不是非模板函数
	cout << lesser(x, y) << endl; // use #1 with int
	//进行显式实例化(使用int替代T)将显式实例化得到的函数。x和y被强制转换为int
	// cin.get();
	return 0;
}

执行结果：

20
15.5
-30
15

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原文地址: http://outofmemory.cn/zaji/5713839.html

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