Constructor in C++ Class

Question

I have two Classes, Player and Game.

class Game
{
        private:
            int maxPlayer;
            Player** playersArray;
        public:
            Game(int maxPlayer);
            ~Game();
}

Each index in playersArray consists of pointers to class Player.The following constructor doesn't work, since this message keeps appearing:

error: invalid use of 'Player::Player' playersArray[i]->Player();
Game::Game(int maxPlayer)
{   this->maxPlayer=maxPlayer;
    this->playersArray = new Player*[maxPlayer];
    for(int i=0;i<maxPlayer;i++)
    {
        playersArray[i]->Player();
    }
}

This is the class Player:

class Player {
        private:
            char* player_name;
            int level;
            int life;
            int strength;
            Weapon player_weapon;
            int place; 
}

My aim is to set the player_name to NULL and NOT to a random place in the memory. This is what Player() is supposed to do.

Already asked https://stackoverflow.com/questions/50750773/classes-in-c-constructor-and-dtor — , Jun 08 '18 at 00:55
@SamerTufail when you use placement new you still do not call ctor directly, new does it for you. — Slava, Jun 08 '18 at 00:56
@Slava not really `new(buffer) T()` where buffer points to where T() should be constructed followed by a explicit call to the ctor. — Samer Tufail, Jun 08 '18 at 00:58
@SamerTufail where do you see explicit call to constructor here? Explicit call to ctor whould be `new(buffer)->T()` or `new(buffer) T->T();` — Slava, Jun 08 '18 at 01:00
Possible duplicate of [Classes in C++ Constructor and D'tor](https://stackoverflow.com/questions/50750773/classes-in-c-constructor-and-dtor) — Tas, Jun 08 '18 at 01:04

Remy Lebeau · Accepted Answer · 2018-06-08T01:12:12.523

You are not populating your Game array correctly. You are trying to call the Player() constructor as if it were a regular class method (which it is not), and worse you are calling it via an uninitialized Player* pointer.

You need to use the new operator instead, eg:

class Game
{
private:
    int maxPlayers;
    Player** playersArray;
public:
    Game(int aMaxPlayers);
    ~Game();
}

Game::Game(int aMaxPlayers)
{
    maxPlayers = aMaxPlayers;
    playersArray = new Player*[maxPlayers];
    for(int i = 0; i < maxPlayers; ++i)
        playersArray[i] = new Player; // <-- here
}

Game::~Game()
{
    for(int i = 0; i < maxPlayers; ++i)
        delete playersArray[i];
    delete[] playersArray;
}

A safer option is to use std::unique_ptr instead of raw pointers:

#include <memory>

class Game
{
private:
    int maxPlayers;
    std::unique_ptr<std::unique_ptr<Player>[]> playersArray;
public:
    Game(int aMaxPlayers);
}

Game::Game(int aMaxPlayers)
{
    maxPlayers = aMaxPlayers;
    playersArray = std::make_unique<std::unique_ptr<Player>[]>(maxPlayers);
    for(int i = 0; i < maxPlayers; ++i)
        playersArray[i] = std::make_unique<Player>();
}

That being said, there is no need to use an array of Player* pointers when an array of Player objects will suffice instead:

class Game
{
private:
    int maxPlayers;
    Player* playersArray;
public:
    Game(int aMaxPlayers);
    ~Game();
}

Game::Game(int aMaxPlayers)
{
    maxPlayers = aMaxPlayers;
    playersArray = new Player[maxPlayers];
}

Game::~Game()
{
    delete[] playersArray;
}

Or:

#include <memory>

class Game
{
private:
    int maxPlayers;
    std::unique_ptr<Player[]> playersArray;
public:
    Game(int aMaxPlayers);
}

Game::Game(int aMaxPlayers)
{
    maxPlayers = aMaxPlayers;
    playersArray = std::make_unique<Player[]>(maxPlayers);
}

Which you can then simplify further by using std::vector instead:

#include <vector>

class Game
{
private:
    std::vector<Player> playersArray;
public:
    Game(int maxPlayers);
}

Game::Game(int maxPlayers)
    : playersArray(maxPlayers)
{
}

Constructor in C++ Class

1 Answers1