C++文件读写之对象的读写

　　　这里以一个简单的学生信息管理系统为例。

　　首先是对象的建立，包括姓名，学号，成绩，学分，等

　　如下：

　　这里面包括两个子对象，

 class Student
 {
 public:
     Student() :score(), birthday(){}//对子对象进行初始化
     ~Student(){}
     void InputInfo();
     void OutPutInfo();
     void ShowInfo();
     bool CreditManage();

     char *getNum(){ return num; }
     char *getName(){ return name; }
     bool getSex(){ return sex; }
     float GetCredit(){ return credit; }
     void swapStudent(Student &stu);
 private:
     char  num[];
     char name[];
     bool sex;
     Score score;//子对象
     Birthday birthday;//子对象
     float credit;
     bool isChanged;
 };

　　然后主要还是文件读写。文件读写包括三个类，其中ifstream和ofstrean从fstream派生而来，可以在创建对象的时候直接初始化，这样比较方便。也可以使用open函数打开文件

　　　　(1) ifstream类,它是从istream类派生的。用来支持从磁盘文件的输入。

　　　　(2) ofstream类,它是从ostream类派生的。用来支持向磁盘文件的输出。

　　　　(3) fstream类,它是从iostream类派生的。用来支持对磁盘文件的输入输出。

　　其中的文件读写的关键函数是read和write，这两个函数可以读写固定长度的数据

　　   istream& read(char *buffer,int len);

　　   ostream& write(const char * buffer,int len);

　　文件操作完毕一定要关闭文件,只需调用close()就行。

　　如file.close();

　　定义一个全局函数用于获取文件中对象的个数，

 int GetNumberFromFile()
 {
     int count = ;//对象个数，即学生人数
     fstream infile("e:\\student.txt",ios::in | ios::binary);//以读方式打开文件
     if (!infile)
     {
         cout<<"open file error!"<<endl;
         getchar();
         exit();
     }
     Student stu;
     while (infile.read((char*)&stu,sizeof(stu)))//强制类型转换为(char*),
     {
         count++;
     }
     infile.close();
     return count;
 }

　　这里的文件读写关键是在read函数,read函数会读取数据一直到文件结束

 basic_istream<Elem, Tr>& read(
     char_type *_Str, //这里是要保存的对象数组的地址
     streamsize _Count//这里是对象的大小
 );

　　因为数据是以二进制保存到文件中的，所以我们不用关心数据的格式，我们知道怎么读取数据就行了。向文件中写入整个对象的好处是将来可以整个读取出来进行操作，不必去考虑细节。

　　写入文件和这个类似

             Student stu1;
             stu1.InputInfo();
             fstream outfile("e:\\student.txt", ios::app | ios::binary);//这里以app方式打开文件进行添加
             if (!outfile)
             {
                 cerr << "open file error!";
             }
             outfile.write((char*)&stu1, sizeof(stu1));
             outfile.close();

以app方式打开文件进行添加，文件内部的位置指针会自动移动移动到文件末尾，直接添加文件到最后。

　　当对文件进行输出时

             fstream infile("e:\\student.txt",ios::in | ios::binary);
             if (!infile)
             {
                 cout<<"open file error!"<<endl;
                 getchar();
                 //exit(0);
             }
             int len = ;
             len = GetNumberFromFile();
             if (len == )
             {
                 cout << "no data!" << endl;
                 ch = '';
                 break;
             }
             Student *stu = new Student[len];//动态申请地址，因为这个数组大小是在运行过程中才能知道的
             cout << "number\tname\tsex\tyear-month-day\tcredit" << endl;
             for (int i = ; i < len;i++)
             {
                 infile.read((char*)&stu[i], sizeof(stu[i]));
                 stu[i].OutPutInfo();
             }
             delete []stu;
             infile.close();

　　

还有一些排序的简单实现在下面的代码中

整个程序代码在这里

 #include <iostream>
 #include "string"
 using namespace std;

 class Student;
 bool SortByCondition(Student stu[],const int &len,const char &conditon);//排序
 void SaveToFile(Student stu[],int num);
 void ReadFromFile(Student stu[],int num);
 int GetNumberFromFile();
 char Menu();
 char SortMenu();

 class Score
 {
 public:
     Score(){ english = , math = ; computer = ; }
     Score(float eng, float mat, float com) :english(eng), math(mat), computer(com){}
     void InputScore()
     {
         cout << "enter english  score:";
         cin>> english;
         cout << "enter math     score:";
         cin >> math;
         cout << "enter computer score:";
         cin >> computer;
     }
     void outputScore()
     {
         cout << english << "\t" << math << "\t" << computer << "\t";
     }
     float ScoreSum()
     {
         return (math + english + computer);
     }
     void swapScore(Score &scor)//对象交换数据
     {
         float ftmp = english;
         english = scor.english;
         scor.english = ftmp;

         ftmp = math;
         math = scor.math;
         scor.math = ftmp;

         ftmp = computer;
         computer = scor.computer;
         scor.computer = ftmp;
     }
 private:
     float english;
     float math;
     float computer;
 };

 class Birthday
 {
 public:
     Birthday(){ year = ; month = ; day = ; }
     Birthday(int ye, int mon, int da) :year(ye), month(mon), day(da){}
     void inputBirthday()
     {
         cout << "enter birthday like \"2014 05 01\":" << endl;
         cin >> year >> month >> day;
     }
     void outputBirthday()
     {
         cout << year << "\-" << month << "\-" << day << "\t";
     }
     void swapBirthday(Birthday &bir)//对象交换数据
     {
         int itmp = year;
         year = bir.year;
         bir.year = itmp;

         itmp = month;
         month = bir.month;
         bir.month = itmp;

         itmp = day;
         day = bir.day;
         bir.day = itmp;
     }
 private:
     int year;
     int month;
     int day;
 };

 class Student
 {
 public:
     Student() :score(), birthday(){}
     ~Student(){}
     void InputInfo();
     void OutPutInfo();
     void ShowInfo();
     bool CreditManage();

     char *getNum(){ return num; }
     char *getName(){ return name; }
     bool getSex(){ return sex; }
     float GetCredit(){ return credit; }
     void swapStudent(Student &stu);//对象交换数据
 private:
     char  num[];
     char name[];
     bool sex;
     Score score;
     Birthday birthday;
     float credit;
     bool isChanged;
 };

student.h

 #include "student.h"
 #include "iostream"
 #include "fstream"
 using namespace std;

 void Student::InputInfo()
 {
     cout << "enter number(字符串)";
     cin >> num;
     cout << "enter name(字符串)";
     cin >> name;
     cout << "enter sex(0表示女，1表示男)";
     cin >> sex;
     score.InputScore();
     birthday.inputBirthday();
     credit = score.ScoreSum() / ;//计算得出学分
 }

 void Student::OutPutInfo()
 {
     cout << num << "\t" << name << "\t" << sex << "\t";
     //score.outputScore();
     birthday.outputBirthday();
     cout << credit << endl;
 }

 char Menu()
 {
     //system("cls");
     cout << "******************************************" << endl;
     cout << "***welcome to student management system***" << endl;
     cout << "******************************************" << endl;
     cout << "please choose the number below:" << endl;
     cout << "1--成绩录入" << endl;
     cout << "2--成绩显示" << endl;
     cout << "3--排序管理" << endl;
     cout << "4--学分管理" << endl;
     cout << "0--退出" << endl;
     char ch = getchar();
     return ch;
 }

 void Student::swapStudent(Student &stu)
 {
     char tmp[];
     strcpy_s(tmp, num);
     strcpy_s(num, stu.num);
     strcpy_s(stu.num, tmp);

     char nam[];
     strcpy_s(nam, name);
     strcpy_s(name, stu.name);
     strcpy_s(stu.name, nam);

     bool btmp = sex;
     sex = stu.sex;
     stu.sex = btmp;

     score.swapScore(stu.score);
     birthday.swapBirthday(stu.birthday);

     float ftmp = credit;
     credit = stu.credit;
     stu.credit = ftmp;

     btmp = isChanged;
     isChanged = stu.isChanged;
     stu.isChanged = btmp;

 }

 char SortMenu()
 {
     cout << "选择要进行排序的方式：";
     cout << "1--学号" << endl;
     cout << "2--姓名" << endl;
     cout << "3--性别" << endl;
     cout << "4--学分" << endl;
     cout << "5--返回上一级" << endl;
     getchar();
     char ch = getchar();
     return ch;
 }

 bool SortByCondition(Student stu[], const int &len, const char &conditon)//排序
 {
     char tmp = conditon;
     int length = len;
     switch (tmp)
     {
     case ''://学号
     {
         for (int i = ; i < length; i++)
         {
             for (int j = ; j < length-i-; j++)
             {
                 if (strcmp((stu[j].getNum()), stu[j + ].getNum()) > )
                 //if (stu[j].getName().compare(stu[j+1].getName()) > 0)
                 {
                     //compare(stu[j].getName(),stu[j+1].getName());
                     //stu[j].getName().compare(stu[j+1].getName());
                     stu[j].swapStudent(stu[j + ]);
                 }
             }
         }
         cout << "学号降序排列" << endl;
         for (int i = ; i < length; i++)
         {
             stu[i].OutPutInfo();
 //             if (i % 10 == 0)
 //             {
 //                 cout << "按下任意键继续显示" << endl;
 //                 getchar();
 //             }
         }
         getchar();
     }
         break;
     case ''://姓名
     {
         for (int i = ; i < length; i++)
         {
             for (int j = ; j < length - i - ; j++)
             {
                 if (strcmp(stu[j].getName(), stu[j + ].getName()) < )
                 //if (stu[j].getNum().compare(stu[j+1].getNum()) > 0)
                 {
                     stu[j].swapStudent(stu[j + ]);
                 }
             }
         }
         cout << "姓名降序排列" << endl;

         for (int i = ; i < length; i++)
         {
             stu[i].OutPutInfo();
 //             if (i % 10 == 0)
 //             {
 //                 cout << "按下任意键继续显示" << endl;
 //                 getchar();
 //             }
         }
         getchar();
     }
         break;
     case ''://性别
     {
         for (int i = ; i < length; i++)
         {
             for (int j = ; j < length - i - ; j++)
             {
                 if (stu[j].getSex() < stu[j + ].getSex())
                 {
                     stu[j].swapStudent(stu[j + ]);
                 }
             }
         }
             cout << "性别降序排列" << endl;
         for (int i = ; i < length; i++)
         {
             stu[i].OutPutInfo();
 //             if (i % 10 == 0)
 //             {
 //                 cout << "按下任意键继续显示" << endl;
 //                 getchar();
 //             }
         }
         getchar();
     }
         break;

     case ''://学分
     {
         for (int i = ; i < length; i++)
         {
             for (int j = ; j < length - i - ; j++)
             {
                 if (stu[j].GetCredit() < stu[j + ].GetCredit())
                 {
                     stu[j].swapStudent(stu[j + ]);
                 }
             }
         }
         cout << "学分降序排列" << endl;
         for (int i = ; i < length; i++)
         {
             stu[i].OutPutInfo();
 //             if (i % 10 == 0)
 //             {
 //                 cout << "按下任意键继续显示" << endl;
 //                 getchar();
 //             }
         }
         getchar();
     }
         break;
     default:
         break;
     }
     return true;
 }

 int GetNumberFromFile()
 {
     int count = ;//对象个数，即学生人数
     fstream infile("e:\\student.txt",ios::in | ios::binary);
     if (!infile)
     {
         cout<<"open file error!"<<endl;
         getchar();
         exit();
     }
     Student stu;
     while (infile.read((char*)&stu,sizeof(stu)))
     {
         count++;
     }
     infile.close();
     return count;
 }

student.cpp

 #include "student.h"
 #include "fstream"
 #include "string"

 int main()
 {
     char ch = Menu();
     int  quit = ;
     while (quit)
     {
         switch (ch)
         {
         case ''://成绩录入
         {
             Student stu1;
             stu1.InputInfo();
             fstream outfile("e:\\student.txt", ios::app | ios::binary);
             if (!outfile)
             {
                 cerr << "open file error!";
             }
             outfile.write((char*)&stu1, sizeof(stu1));
             outfile.close();

             ch = '';
             getchar();
         }
             break;
         case ''://成绩显示
         {
             fstream infile("e:\\student.txt",ios::in | ios::binary);
             if (!infile)
             {
                 cout<<"open file error!"<<endl;
                 getchar();
                 //exit(0);
             }
             int len = ;
             len = GetNumberFromFile();
             if (len == )
             {
                 cout << "no data!" << endl;
                 ch = '';
                 break;
             }
             Student *stu = new Student[len];
             cout << "number\tname\tsex\tyear-month-day\tcredit" << endl;
             for (int i = ; i < len;i++)
             {
                 infile.read((char*)&stu[i], sizeof(stu[i]));
                 stu[i].OutPutInfo();
             }
             delete []stu;
             infile.close();
             ch = '';
             getchar();
         }
             break;
         case ''://排序管理
         {
             char condtion = SortMenu();
             fstream file("e:\\student.txt", ios::in | ios::binary);
             if (!file)
             {
                 cerr << "open file error!";
             }
             int len = GetNumberFromFile();
             Student *stu = new Student[len];
             for (int i = ; i < len;i++)
             {
                 file.read((char *)&stu[i], sizeof(stu[i]));
             }

             file.close();
             SortByCondition(stu,len, condtion);

             delete []stu;
             getchar();
         }
             break;

         case ''://学分管理
         {

         }
             break;

         case '':
         {
             quit = ;
             exit();
             ch = '';//quit switch
         }
             break;
         default:
             //ch = '0';
             break;
         }
         //getchar();

         ch = Menu();
     }
     system("pause");
     return ;
 }

main.cpp