用c++写一个数据库

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第一步：构建一个头文件（**.h）  
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#include<iostream>  
#include<iomanip>  
#include<fstream>  
#include<string>  
using namespace std;  
class CStudentRec  
{  
public:  
    char chFlag;//标志，A表示正常，N表示空  
    char strName[20];//姓名  
    char strID[10];//学号  
    float fScore[3];//3门成绩  
    float fAve;//总平均分  
    CStudentRec(char *name,char *id,float score[]);  
    CStudentRec(){chFlag='N';};//默认构造函数  
    ~CStudentRec(){};//默认析构函数  
    void Input(void);  
    float Validate(void);//成绩数据的输入验证，返回正确值  
    void Print(bool isTitle=false);  
    friend ostream& operator<<( ostream& os,CStudentRec& stu);  
    friend istream& operator>>( istream& is,CStudentRec& stu);  
};  
  
CStudentRec::CStudentRec(char *name,char *id,float score[])  
{  
    strncpy(strName,name,20);  
    strncpy(strID,id,10);  
    fAve=0;  
    for(int i=0;i<3;i++)  
    {  
        fScore[i]=score[i];  
        fAve+=fScore[i];  
    }  
    fAve=float(fAve/3.0);  
    chFlag='A';  
}  
void CStudentRec::Input(void)  
{  
    cout<<"姓名：";  
    cin>>strName;  
    cout<<"学号：";  
    cin>>strID;  
    float fSum=0;  
    for(int i=0;i<3;i++)  
    {  
        cout<<"成绩"<<i+1<<":";  
        fScore[i]=Validate();  
        fSum+=fScore[i];  
    }  
    fAve=(float)(fSum/3.0);  
    chFlag='A';  
    getchar();  
}  
float CStudentRec::Validate(void)  
{  
    int s;  
    char buf[80];  
    float res;  
    for(;;)  
    {  
        cin>>res;  
        s=cin.rdstate();  
        while(s)  
        {  
            cin.clear();  
            cin.getline(buf,80);  
            cout<<"非法输入，重新输入：";  
            cin>>res;  
            s=cin.rdstate();  
        }  
        if((res<=100.0)&&(res>=0.0))break;  
        else  
            cout<<"输入的成绩超过范围！请重新输入：";  
    }  
    return res;  
}  
void CStudentRec::Print(bool isTitle)  
{  
    cout.setf(ios::left);  
    if(isTitle)  
        cout<<setw(20)<<"姓名："<<setw(10)<<"学号："<<"	成绩1："<<"	成绩2："<<"	成绩3："<<"	平均分："<<endl;  
    cout<<setw(20)<<strName<<setw(10)<<strID;  
    for(int i=0;i<3;i++)  
        cout<<"	"<<fScore[i];  
    cout<<"	"<<fAve<<endl;  
    getchar();  
}  
ostream& operator<<(ostream& os,CStudentRec& stu)  
{  
    os.write(&stu.chFlag,sizeof(char));  
    os.write(stu.strName,sizeof(stu.strName));  
    os.write(stu.strID,sizeof(stu.strID));  
    os.write((char*)&stu.fScore,sizeof(float)*3);  
    os.write((char*)&stu.fAve,sizeof(float));  
    return os;  
}  
istream& operator>>(istream& is,CStudentRec& stu)  
{  
    char name[20],id[10];  
    is.read(&stu.chFlag,sizeof(char));  
    is.read(name,sizeof(name));  
    is.read(id,sizeof(id));  
    is.read((char*)stu.fScore,sizeof(float)*3);  
    is.read((char*)&stu.fAve,sizeof(float));  
    strncpy(stu.strName,name,sizeof(name));  
    strncpy(stu.strID,id,sizeof(id));  
    return is;  
}  
  
class CStuFile  
{  
public:  
    CStuFile(char* filename);  
    ~CStuFile();  
    void Add(CStudentRec stu);  
    int Seek(char* id,CStudentRec &stu);  
    int List(int nNum=-1);  
private:  
    char* strFileName;  
};  
CStuFile::CStuFile(char* filename)  
{  
    strFileName=new char[strlen(filename)+1];  
    strcpy(strFileName,filename);  
}  
CStuFile::~CStuFile()  
{  
    if(strFileName)delete []strFileName;  
}  
void CStuFile::Add(CStudentRec stu)  
{  
    fstream file(strFileName,ios::out|ios::app|ios::binary);  
    file<<stu;  
    file.close();  
}  
int CStuFile::Seek(char* id,CStudentRec& stu)  
{  
    int nRec=-1;  
    fstream file(strFileName,ios::in|ios::_Nocreate);  
    if(!file)  
    {  
        cout<<"文件"<<strFileName<<"不能打开！
";  
        return nRec;  
    }  
    int i=0;  
    while(!file.eof())  
    {  
        file>>stu;  
        if((strcmp(id,stu.strID)==0)&&(stu.chFlag!='N'))  
        {  
            nRec=i;break;  
        }  
        i++;  
    }  
    file.close();  
    return nRec;  
    getchar();  
}  
int CStuFile::List(int nNum)  
{  
    fstream file(strFileName,ios::in|ios::_Nocreate);  
    if(!file)  
    {  
        cout<<"文件"<<strFileName<<"不能打开！
";  
        return 0;  
    }  
    int nRec=0;  
    if((nNum==-1)||(nNum>0))  
    {  
        cout.setf(ios::left);  
        cout<<setw(6)<<"记录"<<setw(20)<<"姓名"<<setw(10)<<"学号"<<"	成绩1	成绩2	成绩3	平均分"<<endl;  
    }  
    while(!file.eof())  
    {  
        CStudentRec data;  
        file>>data;  
        if(data.chFlag=='A')  
        {  
            nRec++;  
            if((nNum==-1)||(nRec<=nNum))  
            {  
                cout.setf(ios::left);  
                cout<<setw(6)<<nRec;  
                data.Print();  
            }  
        }  
    }  
    file.close();  
    return nRec;  
}  
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第二部：创建一个.cpp文件  
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#include<iostream>  
#include"**.h"  
CStuFile theStu("student.txt");  
void AddTo(int nNum)  
{  
 CStudentRec stu;  
 for(int i=0;i<nNum;i++)  
 {  
  cout<<"请输入第"<<i+1<<"记录:"<<endl;  
  stu.Input();  
  theStu.Add(stu);  
 }  
}  
void main()  
{  
 AddTo(3);  
 theStu.List();  
 CStudentRec one;  
 if(theStu.Seek("21050102",one)>=0)  
  one.Print(true);  
 else  
  cout<<"没有找到！
";  
 theStu.List();  
 getchar();  
}  
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ok