c++ file handling - class objects - c++

Question

The following code read 3 obj and write them into a file.
however im unable to retrieve objects properly using the below code.
data is duplicated and is not in order
plz help
old code :
#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();
}
Also please tell me how to put code into stackoverflow. Manually putting 4 spaces after copy pasting is very tiresome
new code after making changes :
#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();
}
Im still facing problem. I write 3 object. But iam getting 4 output records. Last one is duplicated.

Answer 1

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