(C++): Problem storing and accessing user login data

Question

This is simplification of my classes (a "gang-management" game logic):

class Player
{
private:
    string nickname, password;
    Gang my_gang; //this player's gang class instance
public:
    //generic functions...
}
//PlayerContainer is a database of all possible players, each player has a specific gang assigned
class PlayerContainer
{
private:
    list<Player> player_list;
public:
    void add_player();
    void remove_player();
    // and many more .....
    void login();
    void sign_up();
}

Now I wanted to test the login/sign up functionality in the console. In main, the program first asks a user for a login, or for a registration (new gang creation).

Following is the login() function definition (only the parts that I thought would be necessary):

//if login() returns false, the rest of the program won't continue. 
//If true is returned, the program forwards to the menu-part.

bool PlayerContainer::login()
{
    string nick, pass;

    cout << endl << "Enter your nickname: ";
    cin >> nick;
    cout << "Enter your password: ";
    cin >> pass;

    list<Player>::iterator it;

    for (it = player_list.begin(); it != player_list.end(); ++it)
    {
        if (it->get_nickname() == nick && it->get_password() == pass)
        {
            return true;
        }
        else
        {
            //breaks the loop and lets the function return false;
        }
    }

    return false;
}

Now the sign_up() function:

void PlayerContainer::sign_up()
{
    string nick, pass, gang_name;

    cout << endl << "Enter your nickname: ";
    cin >> nick;
    cout << "Enter your password: ";
    cin >> pass;

    list<Player>::iterator it;

    /*Check whether there are no known players*/
    for (it = player_list.begin(); it != player_list.end(); ++it)
    {
        if (it->get_nickname() == nick)
        {
            cout << endl << "ERROR: Player [" << it->get_nickname() << "] already exists!";
            return;
        }
    }

    cout << "\tCreate your gang" << endl << "Enter name of your gang: ";
    cin >> gang_name;

    Gang* g = new Gang(gang_name);

    Player* tmpp = new Player(nick, pass, *g);
    player_list.push_back(*tmpp); //store the temp player in the player list

    cout << endl << "Gang created successfully";
}

EXPECTATIONS:

after signing up, the user "account" data should be stored in list<Player> player_list.

PROBLEM:

when trying signing up after logging in, the login function won't evaluate true (won't let me in).

From what I tried by observing the code behaviour, it seems it's never really saved in player_list. It must have "slipped through". I'm blaming this part of code:

Player* tmpp = new Player(nick, pass, *g);
player_list.push_back(*tmpp); //store the temp player in the player list

I'd be very thankful for any insights!

Why are you using `new`, and not simply `player_list.push_back(Player(nick, pass, Gang(gang_name)));`? Also, there is no need for `Gang` to be dynamically allocated. — PaulMcKenzie, Jul 28 '20 at 01:51

Swordfish · Accepted Answer · 2020-07-28T02:19:07.480

    list<Player>::iterator it;

    for (it = player_list.begin(); it != player_list.end(); ++it)
    {
        if (it->get_nickname() == nick && it->get_password() == pass)
        {
            return true;
        }
        else
        {
            //breaks the loop and lets the function return false;
        }
    }

The else-Block will break the search on the first mismatch. After you fixed your search functionality consider overloading operator==() and using std::find().

Btw: std::list<> is almost always inappropriate. Use std::deque<> or std::vector<>. In which scenario do I use a particular STL container?

Btw2:

   list<Player>::iterator it;

   for (it = player_list.begin(); it != player_list.end(); ++it)

~~>

for (auto it{ player_list.begin() }; it != player_list.end(); ++it) // ...

~~>

for (auto const &player : player_list) // ...

Btw3: I don't know what your game will be like but I'd assume a gang would have multiple members and not every player wants to found it's own gang but rather join an existing one. Maybe you want to reconsider your data model.

Thanks very much! It worked 110%. Also, thank you for pointing out what I should improve. I'm still pretty new to c++ and I'm always up to find out new proper ways of using it. Thanks for your insight! EDIT:Btw3: The players would be gang leaders and would fight against other players' gangs with their own. :-) But I know it still may have whole bunch of other flaws — DemoVision, Jul 28 '20 at 02:23
@DemoVision Please also follow PaulMcKenzie's advice: `new` is hardly ever used in modern C++ (when you aren't writing libraries but user code). If you have to use dynamically created objects use a container or a smart pointer. — Swordfish, Jul 28 '20 at 02:29

(C++): Problem storing and accessing user login data

1 Answers1