Getting the same output twice when reading a file - c++

Question

I am having a problem with the following program,
#include<iostream>
#include<fstream>
#include<windows.h>
using namespace std;
class student
{
int rollno;
char name[50];
int cls;
int marks;
char grade;
public:
void getdata()
{
cout<<"Enter Roll No.: ";
cin>>rollno;
cout<<"Enter Name: ";
cin>>name;
cout<<"Enter Class: ";
cin>>cls;
cout<<"Enter Marks: ";
cin>>marks;
if(marks>=75)
{
grade='A';
}
if(marks>=60 && marks<75)
{
grade='B';
}
if(marks>=45 && marks<60)
{
grade='C';
}
if(marks>=35 && marks<45)
{
grade='D';
}
if(marks<35)
{
grade='F';
}
}
void display()
{
cout<<"\nRoll No.: "<<rollno;
cout<<"\nName: "<<name;
cout<<"\nClass: "<<cls;
cout<<"\nMarks: "<<marks;
cout<<"\nGrade: "<<grade<<endl;
}
int rno()
{
return rollno;
}
} s1, s2, s3;
void append()
{
fstream fo ("STUDENT.DAT",ios::binary | ios::app | ios::out);
if(!fo)
{
cout<<"CANNOT OPEN FILE!!!!!";
}
else
{
s1.getdata();
fo.write((char*)&s1, sizeof(s1));
}
fo.close();
}
void sdisplay()
{
fstream fi ("STUDENT.DAT",ios::binary | ios::in);
if(!fi)
{
cout<<"\nNO RECORDS !!!!";
}
else
{
while(!fi.eof())
{
fi.read((char*)&s2, sizeof(s2));
if(s2.rno()!='\0')
{
s2.display();
}
}
}
fi.close();
}
void rdisplay()
{
int n, found;
fstream fi ("STUDENT.DAT", ios::in | ios::binary);
if(!fi)
{
cout<<"\nNO RECORDS !!!!";
}
else
{
cout<<"\nEnter Roll No. to be displayed: ";
cin>>n;
while(!fi.eof())
{
fi.read((char*)&s3, sizeof(s3));
if(s3.rno()==n)
{
s3.display();
found=1;
}
}
if(found!=1)
{
cout<<"\nCannot find roll no!!";
}
}
fi.close();
}
int main()
{
char ch='y';
int choice, n;
while(ch=='y' || ch=='Y')
{
cout<<"\n1. Append Data to File";
cout<<"\n2. Display Entire File";
cout<<"\n3. Search & Display record based on Roll No.";
cout<<"\n4. Exit";
cout<<"\n\n Enter your choice (1-4): ";
cin>>choice;
switch(choice)
{
case 1:
append();
break;
case 2:
sdisplay();
break;
case 3:
rdisplay();
break;
case 4:
exit(0);
break;
default:
cout<<"\nWrong Choice !!!!!";
break;
}
cout<<"\n\nDo you want to continue? (Y/N)";
cin>>ch;
}
}
So, After appending the data, When I go to Display the data (option 2 & 3) it outputs the same entry twice.
Append Data to File
Display Entire File
Search & Display record based on Roll No.
Exit
Enter your choice (1-4): 2
NO RECORDS !!!!
Do you want to continue? (Y/N)y
Append Data to File
Display Entire File
Search & Display record based on Roll No.
Exit
Enter your choice (1-4): 1 Enter Roll No.: 23 Enter Name: James Enter
Class: 12 Enter Marks: 85
Do you want to continue? (Y/N)y
Append Data to File
Display Entire File
Search & Display record based on Roll No.
Exit
Enter your choice (1-4): 2
Roll No.: 23 Name: James Class: 12 Marks: 85 Grade: A
Roll No.: 23 Name: James Class: 12 Marks: 85 Grade: A
Do you want to continue? (Y/N)n
Process returned 0 (0x0) execution time : 25.013 s Press any key to
continue.
Can someone help me?
Thanks

Answer 1

eof() won't get set until you read past the end, which won't happen until your 2nd read. That read will do nothing, so it won't overwrite s2, it'll just fail - so you'll end up printing that row again.
The solution is don't loop over eof(). Just loop over read():
while(fi.read((char*)&s2, sizeof(s2)))
{
s2.display();
}