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[];//姓名
     char strID[];//学号
     float fScore[];//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,);
     strncpy(strID,id,);
     fAve=;
     for(int i=;i<;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=;
     for(int i=;i<;i++)
     {
         cout<<"成绩"<<i+<<":";
         fScore[i]=Validate();
         fSum+=fScore[i];
     }
     fAve=(float)(fSum/3.0);
     chFlag='A';
     getchar();
 }
 float CStudentRec::Validate(void)
 {
     int s;
     char buf[];
     float res;
     for(;;)
     {
         cin>>res;
         s=cin.rdstate();
         while(s)
         {
             cin.clear();
             cin.getline(buf,);
             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()<<"姓名："<<setw()<<"学号："<<"\t成绩1："<<"\t成绩2："<<"\t成绩3："<<"\t平均分："<<endl;
     cout<<setw()<<strName<<setw()<<strID;
     for(int i=;i<;i++)
         cout<<"\t"<<fScore[i];
     cout<<"\t"<<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)*);
     os.write((char*)&stu.fAve,sizeof(float));
     return os;
 }
 istream& operator>>(istream& is,CStudentRec& stu)
 {
     char name[],id[];
     is.read(&stu.chFlag,sizeof(char));
     is.read(name,sizeof(name));
     is.read(id,sizeof(id));
     is.read((char*)stu.fScore,sizeof(float)*);
     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=-);
 private:
     char* strFileName;
 };
 CStuFile::CStuFile(char* filename)
 {
     strFileName=new char[strlen(filename)+];
     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=-;
     fstream file(strFileName,ios::in|ios::_Nocreate);
     if(!file)
     {
         cout<<"文件"<<strFileName<<"不能打开！\n";
         return nRec;
     }
     int i=;
     while(!file.eof())
     {
         file>>stu;
         if((strcmp(id,stu.strID)==)&&(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！\n";
         return ;
     }
     int nRec=;
     if((nNum==-)||(nNum>))
     {
         cout.setf(ios::left);
         cout<<setw()<<"记录"<<setw()<<"姓名"<<setw()<<"学号"<<"\t成绩1\t成绩2\t成绩3\t平均分"<<endl;
     }
     while(!file.eof())
     {
         CStudentRec data;
         file>>data;
         if(data.chFlag=='A')
         {
             nRec++;
             if((nNum==-)||(nRec<=nNum))
             {
                 cout.setf(ios::left);
                 cout<<setw()<<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=;i<nNum;i++)
  {
   cout<<"请输入第"<<i+<<"记录:"<<endl;
   stu.Input();
   theStu.Add(stu);
  }
 }
 void main()
 {
  AddTo();
  theStu.List();
  CStudentRec one;
  if(theStu.Seek("",one)>=)
   one.Print(true);
  else
   cout<<"没有找到！\n";
  theStu.List();
  getchar();
 }
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 ok