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[10];
    char name[20];
    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 = 0;//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(0);
    }
    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 = 0;
            len = GetNumberFromFile();
            if (len == 0)
            {
                cout << "no data!" << endl;
                ch = '0';
                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	name	sex	year-month-day	credit" << endl;            
            for (int i = 0; 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 = 0, math = 0; computer = 0; }
    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 << "	" << math << "	" << computer << "	";
    }
    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 = 0; month = 0; day = 0; }
    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 << "	";
    }
    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[10];
    char name[20];
    bool sex;
    Score score;
    Birthday birthday;
    float credit;
    bool isChanged;
};

#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() / 10;//计算得出学分
}

void Student::OutPutInfo()
{
    cout << num << "	" << name << "	" << sex << "	";
    //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[10];
    strcpy_s(tmp, num);
    strcpy_s(num, stu.num);
    strcpy_s(stu.num, tmp);

    char nam[20];
    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 '1'://学号
    {
        for (int i = 0; i < length; i++)
        {
            for (int j = 0; j < length-i-1; j++)
            {
                if (strcmp((stu[j].getNum()), stu[j + 1].getNum()) > 0)
                //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 + 1]);
                }
            }
        }
        cout << "学号降序排列" << endl;
        for (int i = 0; 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 '2'://姓名
    {
        for (int i = 0; i < length; i++)
        {
            for (int j = 0; j < length - i - 1; j++)
            {
                if (strcmp(stu[j].getName(), stu[j + 1].getName()) < 0)
                //if (stu[j].getNum().compare(stu[j+1].getNum()) > 0)
                {
                    stu[j].swapStudent(stu[j + 1]);
                }
            }
        }
        cout << "姓名降序排列" << endl;

        for (int i = 0; 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 '3'://性别
    {
        for (int i = 0; i < length; i++)
        {
            for (int j = 0; j < length - i - 1; j++)
            {
                if (stu[j].getSex() < stu[j + 1].getSex())
                {
                    stu[j].swapStudent(stu[j + 1]);
                }
            }
        }
            cout << "性别降序排列" << endl;
        for (int i = 0; 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 '4'://学分
    {
        for (int i = 0; i < length; i++)
        {
            for (int j = 0; j < length - i - 1; j++)
            {
                if (stu[j].GetCredit() < stu[j + 1].GetCredit())
                {
                    stu[j].swapStudent(stu[j + 1]);
                }
            }
        }
        cout << "学分降序排列" << endl;
        for (int i = 0; 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 = 0;//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(0);
    }
    Student stu;
    while (infile.read((char*)&stu,sizeof(stu)))
    {
        count++;
    }
    infile.close();
    return count;
}

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

int main()
{
    char ch = Menu();
    int  quit = 1;
    while (quit)
    {
        switch (ch)
        {
        case '1'://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 = '0';
            getchar();
        }
            break;
        case '2'://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 = 0;
            len = GetNumberFromFile();
            if (len == 0)
            {
                cout << "no data!" << endl;
                ch = '0';
                break;
            }
            Student *stu = new Student[len];
            cout << "number	name	sex	year-month-day	credit" << endl;            
            for (int i = 0; i < len;i++)
            {
                infile.read((char*)&stu[i], sizeof(stu[i]));
                stu[i].OutPutInfo();
            }
            delete []stu;
            infile.close();
            ch = '0';
            getchar();
        }
            break;
        case '3'://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 = 0; i < len;i++)
            {
                file.read((char *)&stu[i], sizeof(stu[i]));
            }
        
            file.close();
            SortByCondition(stu,len, condtion);


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

        case '4'://学分管理
        {

        }
            break;

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

        ch = Menu();
    }
    system("pause");
    return 0;
}