I need help with tellg(). I have pasted the code and where I need help.

Question

#include<iostream>
#include<fstream>
#include<iomanip>
#include<string>

using namespace std;
class Item
{
string name;
int code;
int cost;

public:
void getData();
void putData();

};

void Item::getData()
{
cout<<"Enter Item Code: "; cin>>code; cin.ignore();
cout<<"Enter Item Name: "; cin>>name; cin.ignore();
cout<<"Enter Item Cost: "; cin>>cost; cin.ignore();
}
void Item::putData()
{
cout<<setiosflags(ios::left)<<setw(10)<<code
<<setw(10)<<name
<<setw(10)<<cost<<endl;
}

int main()
{

Item it[2], out; //two objects of item class.

fstream file;
file.open("item.txt", ios::in | ios::out | ios::trunc);

for(int i=0; i<2; i++)
{
it[i].getData();
file.write(reinterpret_cast<char *>(&it[i]), sizeof(Item));
}

file.seekg(0);

cout<<setiosflags(ios::left)<<setw(10)<<"Code"<<setw(10)
<<"Name" << setw(10)
<<"Cost"<<endl;

while(true)
{

file.read(reinterpret_cast<char *>(&out), sizeof(Item));
if(file.eof())
{
break;

}
out.putData();
}
file.seekg(0);

//Everything works fine above this. In fact, if I were to remove "file.read" code, everything works as expected below too, the tellg() used below returns the right position; but if I include the code, it returns -1 and -1. Why???? And How can I resolve this?

//My question starts from here.

int pos1=file.tellg(); //I am pretty sure the compiler is confused here, there two objects "it" and "out", and the file pointer doesn't know where to direct.

file.seekg(0, ios::end); //I want to know the end.

int pos2=file.tellg();

cout<<"\n\nPos1 and Pos2: "<<pos1<<" "<<pos2<<endl; //This gives me -1 and -1 as answers.

file.close();
}

Answer 1

I found the answer.
I am supposed to use file.clear() below this code

while(true)
{

file.read(reinterpret_cast<char *>(&out), sizeof(Item));
if(file.eof())
{
break;

}
out.putData();
}

file.clear(); //added this

This got the answer. I read something like "Eof Flag off" --I couldn't understand this. What I understood was, when EOF is called, it adds something to the file that the file is no more available for anything, file.clear() removes that "flag".

I would love an explanation.