04737_C++程序设计_第9章_运算符重载及流类库

例9.1

完整实现str类的例子。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>
 #include <string>

 using namespace std;

 class str
 {
 private:
     char *st;
 public:
     str(char *s);//使用字符指针的构造函数
     str(str& s);//使用对象引用的构造函数
     str& operator=(str& a);//重载使用对象引用的赋值运算符
     str& operator=(char *s);//重载使用指针的赋值运算符
     void print()
     {
         cout << st << endl;//输出字符串
     }
     ~str()
     {
         delete st;
     }
 };

 str::str(char *s)
 {
     st = new char[strlen(s) + ];//为st申请内存
     strcpy(st, s);//将字符串s复制到内存区st
 }

 str::str(str& a)
 {
     st = new char[strlen(a.st) + ];//为st申请内存
     strcpy(st, a.st);//将对象a的字符串复制到内存区st
 }

 str& str::operator=(str& a)
 {
     if (this == &a)//防止a=a这样的赋值
     {
         return *this;//a=a，退出
     }
     delete st;//不是自身，先释放内存空间
     st = new char[strlen(a.st) + ];//重新申请内测
     strcpy(st, a.st);//将对象a的字符串复制到申请的内存区
     return *this;//返回this指针指向的对象
 }

 str& str::operator=(char *s)
 {
     delete st;//是字符串直接赋值，先释放内存空间
     st = new char[strlen(s) + ];//重新申请内存
     strcpy(st, s);//将字符串s复制到内存区st
     return *this;
 }

 void main()
 {
     str s1("We"), s2("They"), s3(s1);//调用构造函数和复制构造函数

     s1.print();
     s2.print();
     s3.print();

     s2 = s1 = s3;//调用赋值操作符
     s3 = "Go home!";//调用字符串赋值操作符
     s3 = s3;//调用赋值操作符但不进行赋值操作

     s1.print();
     s2.print();
     s3.print();

     system("pause");
 };

例9.2

使用友元函数重载运算符“<<”和“>>”。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>

 using namespace std;

 class test
 {
 private:
     int i;
     float f;
     char ch;
 public:
     test(int a = , float b = , char c = '\0')
     {
         i = a;
         f = b;
         ch = c;
     }
     friend ostream &operator<<(ostream &, test);
     friend istream &operator>>(istream &, test &);
 };

 ostream &operator<<(ostream & stream, test obj)
 {
     stream << obj.i << ",";
     stream << obj.f << ",";
     stream << obj.ch << endl;
     return stream;
 }

 istream &operator>>(istream & t_stream, test &obj)
 {
     t_stream >> obj.i;
     t_stream >> obj.f;
     t_stream >> obj.ch;
     return t_stream;
 }

 void main()
 {
     test A(, 8.5, 'W');

     cout << A;

     test B, C;

     cout << "Input as i f ch:";

     cin >> B >> C;

     cout << B << C;

     system("pause");
 };

例9.3

使用类运算符重载“++”运算符。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>

 using namespace std;

 class number
 {
     int num;
 public:
     number(int i)
     {
         num = i;
     }
     int operator++();//前缀：++n
     int operator++(int);//后缀：n++
     void print()
     {
         cout << "num=" << num << endl;
     }
 };

 int number::operator++()
 {
     num++;
     return num;
 }

 int number::operator++(int)//不用给出形参名
 {
     int i = num;
     num++;
     return i;
 }

 void main()
 {
     number n();

     int i = ++n;//i=11,n=11
     cout << "i=" << i << endl;//输出i=11
     n.print();//输出n=11

     i = n++;////i=11,n=12
     cout << "i=" << i << endl;//输出i=11
     n.print();//输出n=12

     system("pause");
 };

例9.4

使用友元运算符重载“++”运算符。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>

 using namespace std;

 class number
 {
     int num;
 public:
     number(int i)
     {
         num = i;
     }
     friend int operator++(number&);//前缀：++n
     friend int operator++(number&, int);//后缀：n++
     void print()
     {
         cout << "num=" << num << endl;
     }
 };

 int operator++(number& a)
 {
     a.num++;
     return a.num;
 }

 int operator++(number& a, int)//不用给出int类型的形参名
 {
     int i = a.num++;
     return i;
 }

 void main()
 {
     number n();

     int i = ++n;//i=11,n=11
     cout << "i=" << i << endl;//输出i=11
     n.print();//输出n=11

     i = n++;////i=11,n=12
     cout << "i=" << i << endl;//输出i=11
     n.print();//输出n=12

     system("pause");
 };

例9.5

使用对象作为友元函数参数来定义运算符“+”的例子。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>

 using namespace std;

 class complex
 {
     double real, imag;
 public:
     complex(double r = , double i = )
     {
         real = r;
         imag = i;
     }
     friend complex operator+(complex, complex);
     void show()
     {
         cout << real << "+" << imag << "i";
     }
 };

 complex operator+(complex a, complex b)
 {
     double r = a.real + b.real;
     double i = a.imag + b.imag;
     return complex(r, i);
 }

 void main()
 {
     complex x(, ), y;

     y = x + ;//12+3i
     y =  + y;//19+3i
     y.show();//输出19+3i

     system("pause");
 };

例9.6

设计类iArray，对其重载下标运算符[]，并能在进行下标访问时检查下标是否越界。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>
 #include <iomanip>

 using namespace std;

 class iArray
 {
     int _size;
     int *data;
 public:
     iArray(int);
     int& operator[](int);
     int size()const
     {
         return _size;
     }
     ~iArray()
     {
         delete[]data;
     }
 };

 iArray::iArray(int n)//构造函数中n>1
 {
     if (n < )
     {
         cout << "Error dimension description";
         exit();
     }
     _size = n;
     data = new int[_size];
 }

 int & iArray::operator[](int i)//合理范围0~_size-1
 {
     if (i <  || i > _size - )//检查越界
     {
         cout << "\nSubscript out of range";
         delete[]data;//释放数组所占内存空间
         exit();
     }
     return data[i];
 }

 void main()
 {
     iArray a();
     cout << "数组元素个数=" << a.size() << endl;

     for (int i = ; i < a.size(); i++)
     {
         a[i] =  * (i + );
     }

     for (int i = ; i < a.size(); i++)
     {
         cout << setw() << a[i];
     }

     system("pause");
 };

例9.7

演示使用标志位的例子。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>

 using namespace std;

 const double PI = 3.141592;

 void main()
 {
     int a = ;
     bool it = , not = ;

     cout << showpoint << 123.0 << " "//输出小数点
         << noshowpoint << 123.0 << " ";//不输出小数点
     cout << showbase;//演示输出数基
     cout << a << " " << uppercase << hex << a << " " << nouppercase//演示大小写
         << hex << a << " " << noshowbase << a << dec << a << endl;

     cout << uppercase << scientific << PI << " " << nouppercase << PI << " " << fixed << PI << endl;

     cout << cout.precision() << " " << PI << " ";//演示cout的成员函数
     cout.precision();
     cout << cout.precision() << " " << PI << endl;

     cout.width();
     cout << showpos << right << a << " " << noshowpos << PI << " ";//演示数值符号
     cout << it << " " << not<< " "
         << boolalpha << it << " " << " " << not<< " "//演示bool
         << noboolalpha << " " << it << " " << not<< endl;

     cout.width();
     cout << left << PI << " " <<  << " " << cout.width() << " ";
     cout <<  << " " << cout.width() << endl;

     system("pause");
 };

例9.8

使用成员函数设置标志位的例子。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>

 using namespace std;

 const double PI = 3.141592;

 void main()
 {
     int a = ;

     cout.setf(ios_base::showpoint);//演示使用setf和unsetf
     cout << 123.0 << " ";
     cout.unsetf(ios_base::showpoint);
     cout << 123.0 << endl;

     cout.setf(ios_base::showbase);
     cout.setf(ios_base::hex, ios_base::basefield);
     cout << a << " " << uppercase << hex << a << " " << nouppercase//比较哪种方便
         << hex << a << " " << noshowbase << a << dec << " " << a << endl;

     float c = 23.56F, d = -101.22F;
     cout.width();
     cout.setf(ios_base::scientific | ios_base::right | ios_base::showpos, ios_base::floatfield);
     cout << c << "\t" << d << "\t";
     cout.setf(ios_base::fixed | ios_base::showpos, ios_base::floatfield);
     cout << c << "\t" << d << "\t";

     cout << cout.flags() << " " << 123.0 << " ";//演示输出flags
     cout.flags();//演示设置flags
     cout << 123.0 << endl;

     cout.setf(ios_base::scientific);//演示省略方式
     cout << 123.0 << endl;

     cout.width();//设置填充字符数量(n-1)
     cout << cout.fill('*') <<  << endl;//演示填充

     system("pause");
 };

例9.9

演示文件流的概念。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>
 #include <fstream>//输入输出文件流头文件

 using namespace std;

 void main()
 {
     int i;

     char ch[], *p = "abcdefg";

     ofstream myFILE;//建立输出流myFILE
     myFILE.open("myText.txt");//建立输出流myFILE和myText.txt之间的关联
     myFILE << p;//使用输出流myFILE将字符串流向文件
     myFILE << "GoodBye!";//使用输出流myFILE直接将字符串流向文
     myFILE.close();//关闭文件myText.txt

     ifstream getText("myText.txt");//建立输入流getText及其和文件myText.txt的关联

     for (i = ; i < strlen(p) + ; i++)//使用输入流getText每次从文件myText.txt读入1个字符
     {
         getText >> ch[i];//将每次读入的1个字符赋给数组的元素
     }
     ch[i] = '\0';//设置结束标志

     getText.close();//关闭文件myText.txt

     cout << ch;//使用cout流向屏幕

     system("pause");
 };

例9.10

演示重载流运算符的例子。

 #define _CRT_SECURE_NO_WARNINGS

 #include <iostream>
 #include <fstream>

 using namespace std;

 struct list
 {
     double salary;
     char name[];
     friend ostream &operator<<(ostream &os, list &ob);
     friend istream &operator>>(istream &is, list &ob);
 };

 istream &operator>>(istream &is, list &ob)//重载”>>“运算符
 {
     is >> ob.name;
     is >> ob.salary;
     return is;
 }

 ostream &operator<<(ostream &os, list &ob)//重载”<<“运算符
 {
     os << ob.name << ' ';
     os << ob.salary << ' ';
     return os;
 }

 void main()
 {
     int i;

     list worker1[] = { {,"LiMing"},{,"ZhangHong"} }, worker2[];
     ofstream out("pay.txt", ios::binary);

     if (!out)
     {
         cout << "没有正确建立文件，结束程序运行！" << endl;
         return;
     }

     for (int i = ; i < ; i++)
     {
         out << worker1[i];//将worker1[i]作为整体对待
     }
     out.close();

     ifstream in("pay.txt", ios::binary);

     if (!in)
     {
         cout << "没有正确建立文件，结束程序运行！" << endl;
         return;
     }

     for (i = ; i < ; i++)
     {
         in >> worker2[i];//将worker2[i]整体读入
         cout << worker2[i] << endl;//将worker2[i]整体输出
     }

     in.close();

     system("pause");
 };

文件存取综合实例

头文件student.h

源文件student.cpp

头文件student.h

 #if ! defined(STUDENT_H)
 #define STUDENT_H
 #include<iostream>
 #include<string>
 #include<iomanip>
 #include<vector>
 #include<fstream>
 using namespace std;

 class student
 {
     string number;
     double score;
 public:
     void SetNum(string s)
     {
         number = s;
     }
     void SetScore(double s)
     {
         score = s;
     }
     string GetNum()
     {
         return number;
     }
     double GetScore()
     {
         return score;
     }
     void set(vector<student>&);//输入信息并存入向量和文件中
     void display(vector<student>&);//显示向量信息
     void read();//读入文件内容
 };
 #endif

源文件student.cpp

 #include"student.h"
 //*******************************
 //* 成员函数:display            *
 //* 参      数:向量对象的引用        *
 //* 返 回 值:无                    *
 //* 功      能:输出向量信息        *
 //*******************************
 void student::display(vector<student>&c)
 {
     cout << "学号" << setw() << "成绩" << endl;
     for (int i = ; i < c.size(); i++)//循环显示向量对象的信息
     {
         cout << c[i].GetNum() << setw() << c[i].GetScore() << endl;
     }
 }
 //*******************************
 //* 成员函数:set                *
 //* 参      数:向量对象的引用        *
 //* 返 回 值:无                    *
 //* 功      能:为向量赋值并将        *
 //             向量内容存入文件    *
 //*******************************
 void student::set(vector<student>&c)
 {
     student a;//定义对象a作为数据临时存储
     string s;//定义临时存储输入学号的对象
     double b;//定义临时存储输入成绩的对象
     while ()//输入数据
     {
         cout << "学号：";
         cin >> s;//取得学号或者结束标志
         if (s == "")//结束输入并将结果存入文件
         {
             ofstream wst("stud.txt");//建立文件stud.txt
             if (!wst)//文件出错处理
             {
                 cout << "没有正确建立文件！" << endl;
                 return;//文件出错结束程序运行
             }
             for (int i = ; i < c.size(); i++)//将向量内存存入文件
             {
                 wst << c[i].number << " " << c[i].score << " ";
             }
             wst.close();//关闭文件
             cout << "一共写入" << c.size() << "个学生的信息。\n";
             return;//正确存入文件后，结束程序运行
         }
         a.SetNum(s);//存入学号
         cout << "成绩：";
         cin >> b;
         a.SetScore(b);//取得成绩
         c.push_back(a);//将a的内容追加到向量c的尾部
     }
 }
 //*******************************
 //* 成员函数:read                *
 //* 参      数:无                    *
 //* 返 回 值:无                    *
 //* 功      能:显示文件内容        *
 //*******************************
 void student::read()
 {
     string number;
     double scroe;
     ifstream rst("stud.txt");//打开文件stud.txt
     if (!rst)//文件出错处理
     {
         cout << "文件打不开\n" << endl;
         return;//文件出错，结束程序运行
     }
     cout << "学号" << setw() << "成绩" << endl;
     while ()//每次读取一条完整信息
     {
         rst >> number >> score;
         if (rst.eof())//判别是否读完文件内容
         {
             rst.close();//读完则关闭文件
             return;//结束程序运行
         }
         cout << number << setw() << score << endl;//显示一条信息
     }
 }

 void main()
 {
     vector<student>st;//向量st的数据类型为double
     student stud;
     stud.set(st);//stud调用成员函数set接受输入并建立文件
     cout << "显示向量数组信息如下：\n";
     stud.display(st);//显示向量内容
     cout << "存入文件内的信息如下：" << endl;
     stud.read();//stud调用read读出文件内容

     system("pause");
 }