C++ File handling error(unhandled exception)

Question

I am trying to write a program where you register a bank account and modify it. This is the code (Not full but just trying to experiment with file handling; I am a beginner at programming)

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


     std::ofstream outfile;
    std::ifstream infile;
    std::fstream inout;

struct bank{
    int acc_nr;
    std::string emri;
    std::string mbiemri;
};


std::istream& operator>> (std::ifstream& in, bank& klient)
{
    in >> klient.emri;
    in >> klient.mbiemri;
    in >> klient.acc_nr;
    return in;
}

std::ostream& operator<< (std::ofstream& out, bank& klient)
{
    out << klient.emri << std::endl;;
    out << klient.mbiemri << std::endl;
    out << klient.acc_nr << std::endl;
    return out;
}

std::ostream& operator<< (std::fstream& out, bank& klient)
{
    out << klient.emri << std::endl;;
    out << klient.mbiemri << std::endl;
    out << klient.acc_nr<< std::endl;
    return out;
}

std::istream& operator>> (std::fstream& in, bank& klient)
{
    in >> klient.emri;
    in >> klient.mbiemri;
    in >> klient.acc_nr;
    return in;
}

std::istream &read(bank &klient, std::istream &is)
{
    std::cout << "Jepni emrin: ";
    is >> klient.emri;
    std::cout << "Jepni mbiemrin: ";
    is >> klient.mbiemri;
    std::cout << "Jep numrin e akaundit: ";
    is >> klient.acc_nr;
    return is;
}

const std::ostream &print(bank klient, std::ostream &os) 
{
    std::cout << "Emri: ";
    os << klient.emri;
    std::cout << "\nMbiemri: ";
    os << klient.mbiemri;
    std::cout << "\nNumri i akaundit: ";
    os << klient.acc_nr;
    return os;
}

void read_infile(bank &klient)
{
    read(klient, std::cin);
    outfile.open("C:\\publik\\sample.dat", std::ios::app| std::ios::binary);
    outfile.write(reinterpret_cast <char *>(&klient), sizeof(bank));
    outfile.close();
}

void print_outfile(bank klient)
{
    infile.open("C:\\publik\\sample.dat", std::ios::in| std::ios::binary);
    infile.read(reinterpret_cast <char *>(&klient), sizeof(bank));
    infile.close();
}

void kerko(std::string emri, std::streampos& a)
{
    bank temp;
    inout.open("C:\\publik\\sample.dat", std::ios::in | std::ios::out | std::ios::binary);
    while (inout.read(reinterpret_cast <char *>(&temp), sizeof(bank)))
    {
        if (emri == temp.emri)  // emri = name.
        {
            print(temp, std::cout);
            a = inout.tellg();
            inout.close();
        break;
        }
    }
}



int main()
{
    bank klient;
    bank temp2;
    std::string emri;
    std::streampos a;
    std::cin >> emri;
    bank temp;
    kerko(emri,a);
    std::cout <<std::endl;
    system("pause");
    return 0;
}

The code reads a name, searches through the file and then displays its information. The searching and displaying are successful but I get this error

Unhandled exception at 0x77CFDF58 (msvcp120d.dll) in Banke.exe: 0xC0000005: Access violation reading location 0x00DCAB9C.

The code does not execute past the print function call in the while loop.

Thank you for your time.

Answer 1

There are several things that are wrong here.

First of all you cannot do this:

read(klient, std::cin);
outfile.open("C:\\publik\\sample.dat", std::ios::app| std::ios::binary);
outfile.write(reinterpret_cast <char *>(&klient), sizeof(bank));

your &klient is a complex structure, using a type (std::string) of which you know nothing about its internal layout. It may have pointers pointing 'outside' of it. To read a record you should so something like this;

bank klient ;
std::ifstream istream("name", std::ios::app| std::ios::binary); // or use open
istream >> klient ;

And here we get to second point. This definition is quite ok (I would have used std::ostream instead of std::ofstream but that's a minor point)

std::ostream& operator<< (std::ofstream& out, bank& klient)
{
    out << klient.emri << std::endl;;
    out << klient.mbiemri << std::endl;
    out << klient.acc_nr << std::endl;
    return out;
}

The main point is that when you want to read emri or mbiemri how do you know where the first ends, and the second starts? The simplest way could be insert a space. It works only if emri/mbiemri do not contain spaces themselves, but for a beginner could be a good starting point.

And that's all for now, you have enough to think about...