Question

I am making a user database. When I try to open the "dataBase.txt" which holds all of the users and passwords, the console pops up (which should happen since it is a console application) but it says that the program has already complete. When I close it, my computer tell me that the program had crashed. The function is saved in a class.

After some debugging the code seems to crash at ifstream fin("dataBase.txt");

No error is returned from the compiler.

The code for the function called is:

void User_Psw::UserCheck()
{
    // read from the database
    ifstream fin("dataBase.txt");

    while (!fin.eof())
    {
        fin >> Usernames[sizeOfDatabase] >> Password[sizeOfDatabase];
        sizeOfDatabase++; //The Number of lines in .txt
    }

    // rest of the program
    cout << "Username: ";
    cin >> username;

    getNameIndex();

    cout << "Password: ";
    cin >> password;

    if(!PasswordMatches())
    {
        cout << "Access denied";
    }
}

I can add more code snippets if asked.

Answer 1

Don’t use fin.eof() to control a loop. That function is only useful after a read has failed.

A likely reason for the crash, however, is that you are assigning to Usernames[sizeOfDatabase], which may be beyond Usernames.capacity(). The canonical way to append and item to a std::vector is to call push_back().

Since your containers are std::vector<std::string>, this is a better approach…

std::string username, password;
while (fin >> username >> password)
{
    Usernames.push_back(username);
    Passwords.push_back(password);
    ++sizeOfDatabase;
}

Of course, if you want to know the number of usernames or passwords once the file has been read, you can call Usernames.size() (which should be the same as Passwords.size()); this may obviate the need to keep sizeOfDatabase.

Personally, I would use a single container for usernames and (salted, hashed) passwords, rather than two separate containers; either std::map<std::string, std::string> or perhaps std::unordered_map<std::string, std::string>, making the password lookup nice and quick per username.