Please correct the error in my program. When i run the program on turbo c++ 3, it output 3 times. Also When i enter more than 1 entry only the last entry is outputted. Also it is outputted 3 times.

#include<fstream.h>
#include<iostream.h>
#include<conio.h>
class student
{
int rollno;
char name[20];
int tm;
public:
void input();
void transfer();
void output();
}
obj;
void student::input()
{
char ch='y';
ofstream outf;
outf.open("mark.dat");
while(ch=='y')
{
cout<<"Enter rollno, name and mark";
cin>>rollno>>name>>tm;
outf.write((char*)&obj,sizeof(obj));
cout<<"Wish to enter more(Y/N)?\n";
cin>>ch;
}
outf.close();
}
void student::transfer()
{
ofstream outf;
ifstream inf;
inf.open("mark.dat");
outf.open("trans.dat");
while(inf)
{
inf.read((char*)&obj,sizeof(obj));
outf.write((char*)&obj,sizeof(obj));
}
outf.close();
inf.close();
}
void student:utput()
{
ifstream inf;
inf.open("trans.dat");
while(inf)
{
inf.read((char*)&obj,sizeof(obj));
cout<<"\nRollno "<<rollno;
cout<<"\nName "<<name;
cout<<"\nTotal "<<tm;
}
inf.close();
}
void main()
{
clrscr();
student obj;
obj.input();
obj.transfer();
obj.output();
getch();
}

Try to get rid of that antique Turbo C++ 3 which was obsolete 10 years ago. You can get an excellent free IDE, Code::Blocks with mingw compiler (GNU C compiler for windows) and join the modern world.

Meanwhile:

#include<fstream.h>   // modern compilers use #include <fstream>
#include<iostream.h>  // modern compilers use #include <iostream>
using namespace std; // needed by modern c++ compilers, maybe not for Turbo
//#include<conio.h>  // not used in standard c++
class student
{
  int rollno;
  char name[20];
  int tm;
public:
  void input();
  void transfer();
  void output();
};       // terminate the class definition here
//obj;   // *************don't instantiate an object in the class definition
void student::input()
{
  char ch='y';
  ofstream outf;
  outf.open( "mark.dat" );
  while ( ch=='y' )
  {
    cout<<"Enter rollno, name and mark";
    cin>>rollno>>name>>tm;
    outf.write(( char* )this,sizeof( student ) ); //******* use "this" pointer and sizeof(student)
    cout<<"Wish to enter more(Y/N)?\n";
    cin>>ch;
  }
  outf.close();
}
void student::transfer()
{
  ofstream outf;
  ifstream inf;
  inf.open( "mark.dat" );
  outf.open( "trans.dat" );
  // **********when you do this you put an extra copy of the last student in outf
//  while ( inf )
//  {
  // instead, read inside the loop control expression this way:
  while( inf.read(( char* )this,sizeof( student ) ) ) {  // ********use "this" pointer and sizeof(student)
    outf.write(( char* )this,sizeof( student ) );   // *********use "this" pointer and sizeof(student)
  }
  outf.close();
  inf.close();
}
void student::output()
{
  ifstream inf;
  inf.open( "trans.dat" );
//  while ( inf ) //******* here you're printing yet another extra copy of the last student
  while (inf.read((char*)this, sizeof(student)))  // ******* again, read inside loop control expression
  {
//    inf.read(( char* )this,sizeof( student ) );
    cout<<"\nRollno "<<rollno;
    cout<<"\nName "<<name;
    cout<<"\nTotal "<<tm;
  }
  inf.close();
}
int main()    // ************ return type of main should be int
{
//  clrscr();
  student obj;
  obj.input();
  obj.transfer();
  obj.output();
  getchar();  //******* I guess getch() is a Turbo C thing; I think not used in most modern compilers
  return 0;
}
Comments
Thanks for the help. From bugmenot.

Thank you very much for taking time to correct my program. I am from India and here we learn about only basics of c++ and our syllabus is based on turbo c++ 3. So i use turbo c++ and i don't know much about c++ programing. So i cannot implement all the instructions you given about modern c++.

I tried your new changes. But i still have some little problems. The program is to transfer content of one file to another. When i input only one entry, the program works. But when more than one entry is used it out puts only 1 or 2. Kindly please correct the problem.

Here is the new code by correcting the previous errors.

#include<fstream.h>
#include<iostream.h>
#include<conio.h>
class student
{
int rollno;
char name[20];
int tm;
public:
	void input();
	void transfer();
	void output();
	};
void student::input()
{
char ch='y';
ofstream outf;
outf.open("mark.dat");
while(ch=='y')
{
cout<<"Enter rollno, name and mark\n";
cin>>rollno>>name>>tm;
outf.write((char*)this,sizeof(student));
cout<<"Wish to enter more(Y/N)?\n";
cin>>ch;
}
outf.close();
}
void student::transfer()
{
ofstream outf;
ifstream inf;
inf.open("mark.dat");
outf.open("trans.dat");
while( inf.read(( char* )this,sizeof(student))) 
{
outf.write(( char* )this,sizeof( student ) );
}
outf.close();
inf.close();
}
void student::output()
{
ifstream inf;
inf.open("trans.dat");
while (inf.read((char*)this, sizeof(student)))
{
inf.read(( char* )this,sizeof( student ) );
cout<<"\nRollno "<<rollno;
cout<<"\tName "<<name;
cout<<"\tTotal "<<tm<<'\n';
}
inf.close();
}
void main()
{
clrscr();
student obj;
obj.input();
obj.transfer();
obj.output();
getch();
}

You forgot to eliminate 1 line -- see below. Also, in future when you post code, type \[code\] before your program and \[/code\] after it, so the indentation will be preserved.

void student::output()
{
ifstream inf;
inf.open("trans.dat");
while (inf.read((char*)this, sizeof(student)))
{
// the next line is consuming another input & discarding the one you just read
//inf.read(( char* )this,sizeof( student ) ); *********delete this
cout<<"\nRollno "<<rollno;
cout<<"\tName "<<name;
cout<<"\tTotal "<<tm<<'\n';
}
inf.close();
}

Thank you very much. That really worked.

At last my program to transfer content of one file to another. Again thanks. Here is the full program for further reference to other users.

#include<fstream.h>
#include<iostream.h>
#include<conio.h>
class student
{
int rollno;
char name[20];
int tm;
public:
	void input();
	void transfer();
	void output();
	};
void student::input()
{
char ch='y';
ofstream outf;
outf.open("mark.dat");
while(ch=='y')
{
cout<<"Enter rollno, name and mark\n";
cin>>rollno>>name>>tm;
outf.write((char*)this,sizeof(student));
cout<<"Wish to enter more(Y/N)?\n";
cin>>ch;
}
outf.close();
}
void student::transfer()
{
ofstream outf;
ifstream inf;
inf.open("mark.dat");
outf.open("trans.dat");
while( inf.read(( char* )this,sizeof(student))) 
{
outf.write(( char* )this,sizeof( student ) );
}
outf.close();
inf.close();
}
void student::output()
{
ifstream inf;
inf.open("trans.dat");
while (inf.read((char*)this, sizeof(student)))
{
cout<<"\nRollno "<<rollno;
cout<<"\tName "<<name;
cout<<"\tTotal "<<tm<<'\n';
}
inf.close();
}
void main()
{
clrscr();
student obj;
obj.input();
obj.transfer();
obj.output();
getch();
}
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