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以下代码读取 3 个 obj 并将它们写入文件。但是我无法使用下面的代码正确检索对象。数据重复且无序

请帮助

旧代码：

#include<fstream.h>
#include<conio.h>

class mail
{
  public:
    char un[25];             // user name
    char pd[25];             // passsword

    void reg(int);

} obj[5];

void mail::reg(int k)
{
  int i;
  i=k;

  clrscr();
  cout<<"Enter user name ( enter unique name )\n";
  cin>>un;


  cout<<"Enter password\n";
  cin>>pd;

  ofstream filout;
  filout.open("email",ios::app||ios::binary);
  if(!filout)
  {
    cout<<"cannot open file\n";
  }
  else
  {
    cout<<"\n "<<i;
    filout.write((char *)&obj[i],sizeof(mail));
    filout.close();
  }

  cout<<"You are now registered. \n";
  getch();

}        // end of sign up or register func

void main()
{

  int t;
  clrscr();
  obj[0].reg(0);
  obj[1].reg(1);
  obj[2].reg(2);

  mail obj2;

  ifstream filein;
  filein.open("email",ios::in||ios::binary);
  if(!filein)
  {
    cout<<"Unable to open file to read\n";
  }
  else
  {
    while(!filein.eof())
    {

      filein.read((char *)&obj2,sizeof(obj2));

      cout<<"username "<<obj2.un<<" passwword "<<obj2.pd<<"\n";
    }
    filein.close();
  }
  getch();

}

另外请告诉我如何将代码放入stackoverflow。复制粘贴后手动放4个空格很累

更改后的新代码：

#include<fstream.h>
#include<conio.h>

struct mail
{
    char un[25];             // user name
    char pd[25];             // passsword
    void reg(int);
} obj[5];

void mail::reg(int k)
{
    int i=k;
    clrscr();
    cout<<"Enter user name ( enter unique name )\n";
    cin>>un;
    cout<<"Enter password\n";
    cin>>pd;

    ofstream filout;
    filout.open("email",ios::app|ios::binary);
    if(!filout) {
        cout<<"cannot open file\n";
    } else {
        cout<<"\n "<<i;
        filout.write((char *)&obj[i],sizeof(mail));
        filout.close();
    }

    cout<<"You are now registered. \n";
    getch();

}   // end of sign up or register func

int main()
{
    int t;
    clrscr();
    obj[0].reg(0);
    obj[1].reg(1);
    obj[2].reg(2);

    mail obj2;

    ifstream filein;
    filein.open("email",ios::in|ios::binary);
    if(!filein) {
        cout<<"Unable to open file to read\n";
    } else {
        while(filein) {
            filein.read((char *)&obj2,sizeof(obj2));

            cout<<"username "<<obj2.un<<" passwword "<<obj2.pd<<"\n";
        }
        filein.close();
    }
    getch();
}

我仍然面临问题。我写了 3 个对象。但是我得到了 4 条输出记录。最后一个是重复的。

4

1 回答 1

2

You have an improper file loop, an EOF() loop is bad practice and often can lead to undefined behavior, a proper loop would be as follows:

filein.read((char *)&obj2,sizeof(obj2));
while(filein)
{
    cout<<"username "<<obj2.un<<" passwword "<<obj2.pd<<"\n";
    filein.read((char *)&obj2,sizeof(obj2));
}

the structure of this loop allows the file to check the file for EOF before reading again, while the eof loop will read the eof in THEN check, leading to some junk at the end.

  • your fileIn variable uses improper flags, you use '||' the logical OR operator instead of the '|' logical bitwise operator. This could be a possible reason for your error.
  • you have some issues with your program, void main() make most people here cringe, main ALWAYS returns int
于 2012-12-18T15:14:21.917 回答