Read a binary file until the end c++

Question

I have class player that contains some attributes. I m filling a file with player's data but i want to assign a new id number every time the function is called in a way that the new player's id will be increased every time. So i made this while loop to read number of players and update the player's new id but this doesn't work and nothing is written in the file.

void Player::create_player()
{
    fstream file;
        Player plyr; string passwordt;
        int aget = 0;
        long int id_nmbert = 0;
        string emailt, ingame_namet, full_namet,yes;
        file.open("player_database.dat", ios::binary | ios::app);

        if (!file.is_open())
            throw exception();
        while (file >> yes)  ///
            id_nmbert++;     ///
        cout << "insert player's full name" << endl;
        cin >> full_namet;
        plyr.full_name = full_namet;
        cout << "insert player's age" << endl;
        cin >> aget;
        plyr.age = aget;
        cout << "insert player's email" << endl;
        cin >> emailt;
        plyr.email = emailt;
        cout << "insert player's password" << endl;
        cin >> password;
        plyr.password = passwordt;
        cout << "insert player's ingame name" << endl;
        cin >> ingame_namet;
        plyr.ingame_name = ingame_namet;
        plyr.id_nmber = id_nmbert;
        file.write((char*)&plyr, sizeof(Player));
        file.close();
}

Tried This but it's even worse.

while (!file.eof())
id_numbert;

There are similar questions but not in c++ :).

Answer 1

The question isn't much specific as for what doesn't work, however, for keeping track of the ID I suggest using a static variable at the top of the function like this:

static int playerid = 0;

The static keyword means that it will only set the variable to zero once, and it will not delete the data after the end of the function. Which means you just save the 'playerid' into the file, then increase it by 1. The next time the function will be called, playerid will be larger by 1.

Edit: while (!file.eof()) doesn't work because you're using ios::app, it already starts at file.eof(), so the loop shouldn't do anything.

Answer 2

I'd recommend storing the players in a text file that you parse instead of storing them as binary data. This has a lot of advantages.

The biggest difficulty with your approach is that you need to design a binary format for your player object. Something like

id+N1+'fullname'+N2+'email'+N3+'ingame-name'
4 bytes id, N1 number of characters in fullname(4 bytes),
the characters in fullname as indicated by N1
same for N2 + email and so on.

This requires fairly complicated logic for reading and writing a player.

On the other hand you could have a text file looking like

1
Yassin Mrabet
20
player@gamers.net
playerino1336
2
Captain Giraffe
55
player1@gamers.net
playerino1337

This is a lot easier to write code for. A new player every fifth getline.

A sample readPlayer member could look like (should probably be static, not super important right now)

Plkayer Player::readPlayer(istream& in){
    std::string str_id;
    std::getline(in, str_id);
    std::string fullname;
    std::getline(in, fullname);
    std::string str_age;
    std::getline(in, str_age);
    std::string email;
    std::getline(in, email);
    std::string player_name;
    std::getline(in, player_name);
    int age = std::stoi(str_age);
    int id = std::stoi(str_id);
    if(!in)  // read was unsuccessful.
        handle_bad_read();
    return Player(id, fullname, age, email, player_name);
}

The return statement of course requires a constructor that accepts exactly those arguments, but that constructor will be useful in many other situations too.