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，

 1 class Student

 2 {

 3 public:

 4     Student() :score(), birthday(){}//对子对象进行初始化

 5     ~Student(){}

 6     void InputInfo();

 7     void OutPutInfo();

 8     void ShowInfo();

 9     bool CreditManage();

10 

11     char *getNum(){ return num; }

12     char *getName(){ return name; }

13     bool getSex(){ return sex; }

14     float GetCredit(){ return credit; }

15     void swapStudent(Student &stu);

16 private:

17     char  num[10];

18     char name[20];

19     bool sex;

20     Score score;//子对象

21     Birthday birthday;//子对象

22     float credit;

23     bool isChanged;

24 };

　　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，

 1 int GetNumberFromFile()

 2 {

 3     int count = 0;//对象个数，即学生人数

 4     fstream infile("e:\\student.txt",ios::in | ios::binary);//以读方式打开文件

 5     if (!infile)

 6     {

 7         cout<<"open file error!"<<endl;

 8         getchar();

 9         exit(0);

10     }

11     Student stu;

12     while (infile.read((char*)&stu,sizeof(stu)))//强制类型转换为(char*),

13     {

14         count++;

15     }

16     infile.close();

17     return count;

18 }

　　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

1 basic_istream<Elem, Tr>& read(

2     char_type *_Str, //这里是要保存的对象数组的地址

3     streamsize _Count//这里是对象的大小

4 );

　　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

1             Student stu1;

2             stu1.InputInfo();

3             fstream outfile("e:\\student.txt", ios::app | ios::binary);//这里以app方式打开文件进行添加

4             if (!outfile)

5             {

6                 cerr << "open file error!";

7             }

8             outfile.write((char*)&stu1, sizeof(stu1));

9             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

 1             fstream infile("e:\\student.txt",ios::in | ios::binary);

 2             if (!infile)

 3             {

 4                 cout<<"open file error!"<<endl;

 5                 getchar();

 6                 //exit(0);

 7             }

 8             int len = 0;

 9             len = GetNumberFromFile();

10             if (len == 0)

11             {

12                 cout << "no data!" << endl;

13                 ch = '0';

14                 break;

15             }

16             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

17             cout << "number\tname\tsex\tyear-month-day\tcredit" << endl;            

18             for (int i = 0; i < len;i++)

19             {

20                 infile.read((char*)&stu[i], sizeof(stu[i]));

21                 stu[i].OutPutInfo();

22             }

23             delete []stu;

24             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

  1 #include <iostream>

  2 #include "string"

  3 using namespace std;

  4 

  5 class Student;

  6 bool SortByCondition(Student stu[],const int &len,const char &conditon);//排序

  7 void SaveToFile(Student stu[],int num);

  8 void ReadFromFile(Student stu[],int num);

  9 int GetNumberFromFile();

 10 char Menu();

 11 char SortMenu();

 12 

 13 class Score

 14 {

 15 public:

 16     Score(){ english = 0, math = 0; computer = 0; }

 17     Score(float eng, float mat, float com) :english(eng), math(mat), computer(com){}

 18     void InputScore()

 19     {

 20         cout << "enter english  score:";

 21         cin>> english;

 22         cout << "enter math     score:";

 23         cin >> math;

 24         cout << "enter computer score:";

 25         cin >> computer;

 26     }

 27     void outputScore()

 28     {

 29         cout << english << "\t" << math << "\t" << computer << "\t";

 30     }

 31     float ScoreSum()

 32     {

 33         return (math + english + computer);

 34     }

 35     void swapScore(Score &scor)//对象交换数据

 36     {

 37         float ftmp = english;

 38         english = scor.english;

 39         scor.english = ftmp;

 40 

 41         ftmp = math;

 42         math = scor.math;

 43         scor.math = ftmp;

 44         

 45         ftmp = computer;

 46         computer = scor.computer;

 47         scor.computer = ftmp;

 48     }

 49 private:

 50     float english;

 51     float math;

 52     float computer;

 53 };

 54 

 55 class Birthday

 56 {

 57 public:

 58     Birthday(){ year = 0; month = 0; day = 0; }

 59     Birthday(int ye, int mon, int da) :year(ye), month(mon), day(da){}

 60     void inputBirthday()

 61     {

 62         cout << "enter birthday like \"2014 05 01\":" << endl;

 63         cin >> year >> month >> day;

 64     }

 65     void outputBirthday()

 66     {

 67         cout << year << "\-" << month << "\-" << day << "\t";

 68     }

 69     void swapBirthday(Birthday &bir)//对象交换数据

 70     {

 71         int itmp = year;

 72         year = bir.year;

 73         bir.year = itmp;

 74 

 75         itmp = month;

 76         month = bir.month;

 77         bir.month = itmp;

 78 

 79         itmp = day;

 80         day = bir.day;

 81         bir.day = itmp;

 82     }

 83 private:

 84     int year;

 85     int month;

 86     int day;

 87 };

 88 

 89 

 90 class Student

 91 {

 92 public:

 93     Student() :score(), birthday(){}

 94     ~Student(){}

 95     void InputInfo();

 96     void OutPutInfo();

 97     void ShowInfo();

 98     bool CreditManage();

 99 

100     char *getNum(){ return num; }

101     char *getName(){ return name; }

102     bool getSex(){ return sex; }

103     float GetCredit(){ return credit; }

104     void swapStudent(Student &stu);//对象交换数据

105 private:

106     char  num[10];

107     char name[20];

108     bool sex;

109     Score score;

110     Birthday birthday;

111     float credit;

112     bool isChanged;

113 };

student.h

 

  1 #include "student.h"

  2 #include "iostream"

  3 #include "fstream"

  4 using namespace std;

  5 

  6 

  7 void Student::InputInfo()

  8 {

  9     cout << "enter number(字符串)";

 10     cin >> num;

 11     cout << "enter name(字符串)";

 12     cin >> name;

 13     cout << "enter sex(0表示女，1表示男)";

 14     cin >> sex;

 15     score.InputScore();

 16     birthday.inputBirthday();

 17     credit = score.ScoreSum() / 10;//计算得出学分

 18 }

 19 

 20 void Student::OutPutInfo()

 21 {

 22     cout << num << "\t" << name << "\t" << sex << "\t";

 23     //score.outputScore();

 24     birthday.outputBirthday();

 25     cout << credit << endl;

 26 }

 27 

 28 char Menu()

 29 {

 30     //system("cls");

 31     cout << "******************************************" << endl;

 32     cout << "***welcome to student management system***" << endl;

 33     cout << "******************************************" << endl;

 34     cout << "please choose the number below:" << endl;

 35     cout << "1--成绩录入" << endl;

 36     cout << "2--成绩显示" << endl;

 37     cout << "3--排序管理" << endl;

 38     cout << "4--学分管理" << endl;

 39     cout << "0--退出" << endl;

 40     char ch = getchar();

 41     return ch;

 42 }

 43 

 44 void Student::swapStudent(Student &stu)

 45 {

 46     char tmp[10];

 47     strcpy_s(tmp, num);

 48     strcpy_s(num, stu.num);

 49     strcpy_s(stu.num, tmp);

 50 

 51     char nam[20];

 52     strcpy_s(nam, name);

 53     strcpy_s(name, stu.name);

 54     strcpy_s(stu.name, nam);

 55 

 56     bool btmp = sex;

 57     sex = stu.sex;

 58     stu.sex = btmp;

 59 

 60     score.swapScore(stu.score);

 61     birthday.swapBirthday(stu.birthday);

 62 

 63     float ftmp = credit;

 64     credit = stu.credit;

 65     stu.credit = ftmp;

 66 

 67     btmp = isChanged;

 68     isChanged = stu.isChanged;

 69     stu.isChanged = btmp;

 70 

 71 }

 72 

 73 char SortMenu()

 74 {

 75     cout << "选择要进行排序的方式：";

 76     cout << "1--学号" << endl;

 77     cout << "2--姓名" << endl;

 78     cout << "3--性别" << endl;

 79     cout << "4--学分" << endl;

 80     cout << "5--返回上一级" << endl;

 81     getchar();

 82     char ch = getchar();

 83     return ch;

 84 }

 85 

 86 bool SortByCondition(Student stu[], const int &len, const char &conditon)//排序

 87 {

 88     char tmp = conditon;

 89     int length = len;

 90     switch (tmp)

 91     {

 92     case '1'://学号

 93     {

 94         for (int i = 0; i < length; i++)

 95         {

 96             for (int j = 0; j < length-i-1; j++)

 97             {

 98                 if (strcmp((stu[j].getNum()), stu[j + 1].getNum()) > 0)

 99                 //if (stu[j].getName().compare(stu[j+1].getName()) > 0)

100                 {

101                     //compare(stu[j].getName(),stu[j+1].getName());

102                     //stu[j].getName().compare(stu[j+1].getName());

103                     stu[j].swapStudent(stu[j + 1]);

104                 }

105             }

106         }

107         cout << "学号降序排列" << endl;

108         for (int i = 0; i < length; i++)

109         {

110             stu[i].OutPutInfo();

111 //             if (i % 10 == 0)

112 //             {

113 //                 cout << "按下任意键继续显示" << endl;

114 //                 getchar();

115 //             }

116         }

117         getchar();

118     }

119         break;

120     case '2'://姓名

121     {

122         for (int i = 0; i < length; i++)

123         {

124             for (int j = 0; j < length - i - 1; j++)

125             {

126                 if (strcmp(stu[j].getName(), stu[j + 1].getName()) < 0)

127                 //if (stu[j].getNum().compare(stu[j+1].getNum()) > 0)

128                 {

129                     stu[j].swapStudent(stu[j + 1]);

130                 }

131             }

132         }

133         cout << "姓名降序排列" << endl;

134 

135         for (int i = 0; i < length; i++)

136         {

137             stu[i].OutPutInfo();

138 //             if (i % 10 == 0)

139 //             {

140 //                 cout << "按下任意键继续显示" << endl;

141 //                 getchar();

142 //             }

143         }

144         getchar();

145     }

146         break;

147     case '3'://性别

148     {

149         for (int i = 0; i < length; i++)

150         {

151             for (int j = 0; j < length - i - 1; j++)

152             {

153                 if (stu[j].getSex() < stu[j + 1].getSex())

154                 {

155                     stu[j].swapStudent(stu[j + 1]);

156                 }

157             }

158         }

159             cout << "性别降序排列" << endl;

160         for (int i = 0; i < length; i++)

161         {

162             stu[i].OutPutInfo();

163 //             if (i % 10 == 0)

164 //             {

165 //                 cout << "按下任意键继续显示" << endl;

166 //                 getchar();

167 //             }

168         }

169         getchar();

170     }

171         break;

172 

173     case '4'://学分

174     {

175         for (int i = 0; i < length; i++)

176         {

177             for (int j = 0; j < length - i - 1; j++)

178             {

179                 if (stu[j].GetCredit() < stu[j + 1].GetCredit())

180                 {

181                     stu[j].swapStudent(stu[j + 1]);

182                 }

183             }

184         }

185         cout << "学分降序排列" << endl;

186         for (int i = 0; i < length; i++)

187         {

188             stu[i].OutPutInfo();

189 //             if (i % 10 == 0)

190 //             {

191 //                 cout << "按下任意键继续显示" << endl;

192 //                 getchar();

193 //             }

194         }

195         getchar();

196     }

197         break;

198     default:

199         break;

200     }

201     return true;

202 }

203 

204 int GetNumberFromFile()

205 {

206     int count = 0;//对象个数，即学生人数

207     fstream infile("e:\\student.txt",ios::in | ios::binary);

208     if (!infile)

209     {

210         cout<<"open file error!"<<endl;

211         getchar();

212         exit(0);

213     }

214     Student stu;

215     while (infile.read((char*)&stu,sizeof(stu)))

216     {

217         count++;

218     }

219     infile.close();

220     return count;

221 }

student.cpp

 

  1 #include "student.h"

  2 #include "fstream"

  3 #include "string"

  4 

  5 int main()

  6 {

  7     char ch = Menu();

  8     int  quit = 1;

  9     while (quit)

 10     {

 11         switch (ch)

 12         {

 13         case '1'://成绩录入

 14         {

 15             Student stu1;

 16             stu1.InputInfo();

 17             fstream outfile("e:\\student.txt", ios::app | ios::binary);

 18             if (!outfile)

 19             {

 20                 cerr << "open file error!";

 21             }

 22             outfile.write((char*)&stu1, sizeof(stu1));

 23             outfile.close();

 24 

 25             ch = '0';

 26             getchar();

 27         }

 28             break;

 29         case '2'://成绩显示

 30         {

 31             fstream infile("e:\\student.txt",ios::in | ios::binary);

 32             if (!infile)

 33             {

 34                 cout<<"open file error!"<<endl;

 35                 getchar();

 36                 //exit(0);

 37             }

 38             int len = 0;

 39             len = GetNumberFromFile();

 40             if (len == 0)

 41             {

 42                 cout << "no data!" << endl;

 43                 ch = '0';

 44                 break;

 45             }

 46             Student *stu = new Student[len];

 47             cout << "number\tname\tsex\tyear-month-day\tcredit" << endl;            

 48             for (int i = 0; i < len;i++)

 49             {

 50                 infile.read((char*)&stu[i], sizeof(stu[i]));

 51                 stu[i].OutPutInfo();

 52             }

 53             delete []stu;

 54             infile.close();

 55             ch = '0';

 56             getchar();

 57         }

 58             break;

 59         case '3'://排序管理

 60         {

 61             char condtion = SortMenu();

 62             fstream file("e:\\student.txt", ios::in | ios::binary);

 63             if (!file)

 64             {

 65                 cerr << "open file error!";

 66             }

 67             int len = GetNumberFromFile();

 68             Student *stu = new Student[len];

 69             for (int i = 0; i < len;i++)

 70             {

 71                 file.read((char *)&stu[i], sizeof(stu[i]));

 72             }

 73         

 74             file.close();

 75             SortByCondition(stu,len, condtion);

 76 

 77 

 78             delete []stu;

 79             getchar();

 80         }

 81             break;

 82 

 83         case '4'://学分管理

 84         {

 85 

 86         }

 87             break;

 88 

 89         case '0':

 90         {

 91             quit = 0;

 92             exit(0);

 93             ch = '0';//quit switch

 94         }

 95             break;

 96         default:

 97             //ch = '0';

 98             break;

 99         }

100         //getchar();

101 

102         ch = Menu();

103     }

104     system("pause");

105     return 0;

106 }

main.cpp