程序清单8.1（inline内联函数）
#include<iostream>
using namespace std; inline double square(double x) {//inline表示内联函数
return x*x;
} void main()
{
double a, b, c = 13.0;
a = square(5.0);
b = square(4.5+7.5);
cout << "a=" << a << ",b=" << b << endl;
cout << "c=" << c << ",c square=" << square(c++) << endl;
cout << "Now c=" <<c<< endl;
system("pause");
}
程序清单8.2+8.3（引用变量）
引用变量的主要用途是作为函数的形参：引用变量做参数，函数将使用原始数据。
#include<iostream>
using namespace std; void main()
{
int rat = ;
int &rodent = rat;//将rodent的类型声明为int&，即指向int变量的引用
cout << "rat=" <<rat<< ",rodent=" <<rodent<< endl;
rodent++;
cout << "Now,rat=" << rat << ",rodent=" << rodent << endl;
cout << "rat address=" << &rat << endl;
cout << "rodent address=" <<&rodent<< endl; cout << "************************************" << endl;
int bunny = ;
rodent = bunny;
cout << "rat=" << rat << ",rodent=" << rodent<<",bunny="<<bunny << endl;
cout << "bunny address=" << &bunny << endl;
cout << "rodent address=" << &rodent << endl; system("pause");
}
临时变量、引用参数和const
如果实参与引用参数不匹配，仅当参数为const引用时，C++将生成临时变量。
程序清单8.6
#include<iostream>
#include<string>
using namespace std; struct free_throw
{
string name;
int made;
int attempt;
float percent;
};
void display(const free_throw &ft) {
cout << "Name=" << ft.name << endl;
cout << "Made=" << ft.made << "\t\t";
cout << "Attempt=" << ft.attempt<< "\t";
cout << "Percent=" << ft.percent<<endl;
}
void set(free_throw &ft) {
if (ft.attempt != )
ft.percent = 100.0f*float(ft.made) / float(ft.attempt);
else
ft.percent = ;
}
free_throw & accumulate(free_throw &target,const free_throw &source) {
target.attempt += source.attempt;
target.made += source.made;
set(target);
return target;
} void main()
{
free_throw one = { "If Branch",, };
free_throw two = { "Andor Knott",, };
free_throw three = { "Min Max",, };
free_throw four = { "Whi Loo",, };
free_throw five = { "Long Long",, };
free_throw team = { "Throw",,};
free_throw dup; set(one);
display(one);
accumulate(team, one);
display(team);
display(accumulate(team,two));
accumulate(accumulate(team, three), four);
display(team);
dup = accumulate(team, five);//返回的team赋给dup
cout << "Displaying team:" << endl;
display(team);//team经过48行代码，已经发生了变化
cout << "Displaying dup after assignment:" << endl;
display(dup);
set(four);
accumulate(dup, five) = four;//four赋给dup
cout << "Displaying dup after ill-advised assignment:" << endl;
display(dup); system("pause");
}
程序清单8.7
string：标准库允许把字符串字面值和字符字面值转换为 string 对象，当把 string 对象和字符字面值以及字符串字面值混在一条语句中使用时，必须确保加法运算符（ + ）的两侧运算对象至少有一个是 string:
#include <iostream>
#include <string>
using namespace std; string version1(const string &s1, const string &s2) {
string tmp;
tmp = s2 + s1 + s2;
return tmp;//返回main函数时，tmp不复存在，但tmp的内容被复制到临时存储单元
}
string & version2(string &s1, const string &s2) {//有副作用，改变了s1的内容
s1 = s2 + s1 + s2;
return s1;
}
string & version3(string &s1, const string &s2) {//坏设计
string tmp;
tmp = s2 + s1 + s2;
return tmp;//返回main函数时，tmp内存已被释放，程序不能引用已经释放的内存
} void main()
{
string input, copy, result;
cout << "Enter a string:";
getline(cin, input);//用于字符串的输入
copy = input;//C++中，string可以直接赋值
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." << endl;
input = copy;
result = version3(input, "@@@");//version3返回地址值时报错，因为该地址已释放
cout << "Your string enhanced:" << result << endl;
cout << "Your original string:" << input << endl; system("pause");
}
程序清单8.8（格式化输入输出）
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
const int LIMIT = ; void file_it(ostream &os,double fo,const double fe[],int n) {//参数os可以指向ostream对象（如cout），也可以指向ofstream对象（如fout）
ios_base::fmtflags initial;//ios_base::fmtflags是存储这种信息所需的数据类型名称
initial = os.setf(ios_base::fixed);//setf(ios_base::fixed)使用定点表示法 表示对象
os.precision();//指定显示多少位小数（假定处于定点模式下）
os << "Focal length of objective:" << fo << " mm"<<endl;
os.setf(ios::showpoint);//使用小数点 表示对象，即使小数部分为0
os.precision();
os.width();//设置下一次输出操作使用的字段宽度，只在显示下一个值时有效
os << "f.1. eyepiece";
os.width();
os << "magnification" << endl;
for (int i = ; i < n; i++)
{
os.width();
os << fe[i];
os.width();
os << int(fo / fe[i] + 0.5) << endl;
}
os.setf(initial);//返回调用它之前有效的所有格式化设置，即将对象回到传递给file_it()之前的状态
//当程序将cout传递给file_it()时，cout的设置将被修改，然后被恢复；fout同样如此
}
void main()
{
ofstream fout;
const char *fn = "ep-data.txt";
fout.open(fn);
if (!fout.is_open()) {
cout << "Can't open "<< fn <<".Bye."<< endl;
exit(EXIT_FAILURE);
}
double objective;
cout << "Enter ……：";
cin >> objective;
double eps[LIMIT];
cout << "Enter XXX" << endl;
for (int i = ; i < LIMIT; i++)
{
cout << "Eyepiece #" << i + << ": ";
cin >> eps[i];
}
file_it(fout, objective, eps, LIMIT);//将数据写入文件ep-data.txt
file_it(cout, objective, eps, LIMIT);//将同样的信息以相同的格式显示到屏幕上
cout << "Done" << endl;
system("pause");
}
以下是一些常见的控制函数的:
dec 置基数为10 相当于"%d"
hex 置基数为16 相当于"%X"
oct 置基数为8 相当于"%o"
setfill(c) 设填充字符为c
setprecision(n) 设显示小数精度为n位
setw(n) 设域宽为n个字符
setioflags(ios::fixed) 固定的浮点显示
setioflags(ios::scientific) 指数表示
setiosflags(ios::left) 左对齐
setiosflags(ios::right) 右对齐
setiosflags(ios::skipws 忽略前导空白
setiosflags(ios::uppercase) 16进制数大写输出
setiosflags(ios::lowercase) 16进制小写输出
setiosflags(ios::showpoint) 强制显示小数点
setiosflags(ios::showpos) 强制显示符号
程序清单8.9（默认参数）
#include <iostream>
using namespace std; const int Size = ;
char *left(const char *str, int n = );//默认n为1 void main()
{
char sample[Size];
cout << "Enter a string:\n";
cin.get(sample, Size);
char *p = left(sample, );//调用此方法后要记得delete
cout << p << endl;
delete[] p; p = left(sample);
cout << p << endl;
delete[] p;
system("pause");
} char *left(const char *str, int n) {//内部使用了new未delete，所以在main函数调用此方法后一定要记得delete
if (n < )
n = ;
char *p = new char[n + ];//new和delete成对出现
int i;
for (i = ; i < n&&str[i]; i++)
p[i] = str[i];
while (i <= n)
p[i++] = '\0';
return p;
}
程序清单8.10（函数重载）
#include <iostream>
using namespace std; char *left(const char *str, int n) {//内部使用了new未delete，所以在main函数调用此方法后一定要记得delete
if (n < )
n = ;
char *p = new char[n + ];//new和delete成对出现
int i;
for (i = ; i < n&&str[i]; i++)
p[i] = str[i];
while (i <= n)
p[i++] = '\0';
return p;
}
unsigned long left(unsigned long num, unsigned ct) {
if (ct == || num == )
return ;
unsigned digit = ;
unsigned long n = num;
while (n /= )
digit++;
if (digit > ct) {
ct = digit - ct;
while (ct--)
num /= ;
return num;
}
else
return num;
}
void main()
{
char *trip = "Hawaii!!";
unsigned long n = ;
int i;
char * temp;
for (i = ; i < ; i++)
{
cout << left(n, i) << endl;
temp = left(trip, i);
cout << temp << endl;
delete[] temp;
}
system("pause");
}
程序清单8.11+12（函数模板，模板重载）
#include <iostream>
using namespace std; template <typename T> //函数模板
void swap2(T &a, T &b) { //引用 不能用swap函数名，用户自己定义的swap()函数与STL库定义的函数重载冲突
T temp;
temp = a;
a = b;
b = temp;
}
template <typename T>
void swap2(T a[], T b[],int n) {
T temp;
for (int i = ; i < n; i++)
{
temp = a[i];
a[i] = b[i];
b[i] = temp;
}
} const int Size = ;
template <class Te>//模板的另一种表示方式
void show(Te a[]) {
for (int i = ; i < Size; i++)
{
cout << a[i] << "\t";
}
cout << endl;
} void main()
{
int i = , j = ;
cout << "i=" << i << ",j=" << j << endl;
swap2(i, j);
cout << "Now,i=" << i << ",j=" << j << endl; double x[Size] = { ,,,, };
double y[] = {,,,,};
show(x);
show(y);
swap2(x, y ,Size);
cout << "Now" << endl;
show(x);
show(y); system("pause");
}
程序清单8.13（模板显示具体化）
#include <iostream>
using namespace std; //模板：交换a、b值
template <typename T>
void Swap(T &a, T &b) {
T temp = a;
a = b;
b = temp;
} struct job {
char name[];
double salary;
int floor;
};
//显示具体化：交换结构体内部成员值
template <> void Swap<job>(job &j1, job &j2) {//引用
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) {//引用
cout << j.name << ":$"<<j.salary<<" on floor "<<j.floor<<endl;
} void main()
{
cout.precision();//指定显示多少位小数（假定处于定点模式下）：看有没有set ios::fixed，如果没有的话, 是代表2位有效数字, 不是3位小数
cout.setf(ios::fixed,ios::floatfield);//ios::fixed设置为定点输出格式，floatfield设置输出时按浮点格式，小数点后有6位数字
int i = , j = ;
cout << "i=" << i << ",j=" << j << endl;
Swap(i, j);
cout << "Now,i=" << i << ",j=" << j << endl; job sue = { "S Y",73000.60, };
job sid = { "S T",78060.72, };
show(sue);
show(sid);
Swap(sue, sid);
show(sue);
show(sid);
system("pause");
}
程序清单8.14
#include <iostream>
using namespace std; template <typename T>
void show(T arr[],int n) {
cout << "template A" << endl;
for (int i = ; i < n; i++)
cout << arr[i] << ' ';
cout << endl;
}
template <typename T>
void show(T * arr[], int n) {//指针数组:[]比*优先级高
cout << "template B" << endl;
for (int i = ; i < n; i++)
cout << *arr[i] << ' ';
cout << endl;
} struct debt {
char name[];
double amount;
}; void main()
{
int thing[] = { ,,,,, };
struct debt mr_E[] = {
{ "I W",2400.0 },
{ "U F",1300.0 },
{ "I S",1800.0 }
};
double *pd[];
for (int i = ; i < ; i++)
pd[i] = &mr_E[i].amount;
cout << "Listen:" << endl;
show(thing, );
cout << "Listen debts:" << endl;
show(pd, ); system("pause");
}
如果去掉 template B ，打印出来的将是地址
程序清单8.15
#include <iostream>
using namespace std; //返回小值
template <typename T>
T lesser(T a,T b) {
return a < b ? a : b;
}
//先取绝对值，再返回绝对值中的小值
int lesser(int a, int b) {
a = a < ? -a : a;
b = b < ? -b : b;
return a < b ? a : b;
} void main()
{
int m = , n = -;
double x = 15.5, y = 25.9;
cout << lesser(m, n) << endl;//调用函数
cout << lesser(x, y) << endl;//调用模板函数
cout << lesser<>(m, n) << endl;//<>表示调用模板函数
cout << lesser<int>(x,y)<<endl;//<int>表示 显示实例化，强转xy值 system("pause");
}