Question

I’ve searched high and low for an answer to this question and have attempted many solutions including forward declaration, pointers, and references. I’m sure I’m just using incorrect syntax somewhere. After many wasted hours, I’ve decided to turn to stack overflow.

I am attempting to code one of my first CPP applications as a learning experience. Right now I have a Player and a Ball object. My Ball object must be able to access some of the member variables and methods in my player object. I have been unable to figure out how to do this. Below is an extremely simplified version of my code. I’ve commented the code that is particularly important.

PlayState.hpp

#ifndef PLAYSTATE_HPP
#define PLAYSTATE_HPP
#include "Player.hpp"
#include "Ball.hpp"

class Player;
class Ball;

class PlayState
{
public:
    PlayState();
    Player player;
    Ball ball;
 };
#endif

PlayState.cpp

#include "PlayState.hpp"

PlayState::PlayState() {
}

void PlayState::update() {

    if (sf::Keyboard::isKeyPressed(sf::Keyboard::W))
    {
        ball.checkCollision();
        player.move(1);
    }
    ball.update();
}

void PlayState::draw()
{
    m_game.screen.clear();
    m_game.screen.draw( player.getSprite() );
    m_game.screen.draw( ball.getSprite() );
    m_game.screen.display();
}

Player.hpp

#ifndef PLAYER_HPP
#define PLAYER_HPP

class Player
{
public:
    Player();
    ~Player();

    void create();
    void setRotation(float);
    void setPosition(float, float);
};
#endif

Player.cpp shouldn’t really be all that important to see.

Ball.hpp

#ifndef BALL_HPP
#define BALL_HPP

class Player; // I don't think forward declaration is what I need???

class Ball
{
public:
    bool picked_up;
    bool throwing;

    Player *player; // this isn't working

    Ball();
    ~Ball();

    bool checkCollision();
};
#endif

Ball.cpp

#include "Ball.hpp"

Ball::Ball() {
    Ball::picked_up = false;
    Ball::throwing = false;
}

Ball::~Ball() {
}

bool Ball::checkCollision()
{
    float ball_position_x = Ball::getPosition().x;
    float ball_position_y = Ball::getPosition().y;

    // I need to access the player object here.
    float x_distance = abs(player.getPosition().x - ball_position_x);
    float y_distance = abs(player.getPosition().y - ball_position_y);

    bool is_colliding = (x_distance * 2 < (player.IMG_WIDTH + Ball::width)) && (y_distance * 2 < (player.IMG_HEIGHT + Ball::height));

    return is_colliding;
}

Answer 1

When you say player, do you mean the exact same player that is in the same playstate object as the current ball object? If so you want to first set up that link, it cannot be done automatically.

PlayState::PlayState() :ball(&player){ //pass pointer to ball of its player?
}

class Ball
...    
Ball(Player *myPlayer);
...

}

Ball::Ball(Player *myPlayer):player(myPlayer) {
...

// I need to access the player object here.
float x_distance = abs(player->getPosition().x - ball_position_x);

You also need to use a pointer to use the player since it is a pointer to a player object.

You do need the forward declaration to Player above the Ball class. The one above Playstate is unnecessary.

Also your player doesnt seem to have a GetPosition function, I am assuming it is a public member function you forgot to include above.