Question

class Game {
  private:
    string title;
    bool running;
    State currentState;

  public:
    sf::RenderWindow window;
    void setup();
    void run();
};

I have a variable called currentState. This is State:

#ifndef STATE_HPP
#define STATE_HPP

using namespace std;

class State {
  private:

  public:
    void start();
    void update();
    void render();
};

#endif

And then I have a class called PlayState, which inherits State:

#ifndef PLAY_STATE_HPP
#define PLAY_STATE_HPP

#include <SFML/Graphics.hpp>

#include "Game.hpp"
#include "State.hpp"

using namespace std;

class PlayState : public State {
  private:
    sf::CircleShape shape;
    Game game;

  public:
    PlayState();
    void start();
    void update();
    void render();
};

#endif

On my Game.cpp, I am creating currentState, by doing:

currentState = PlayState();

The problem is, though, that it’s not working. currentState.update() is state.update(). It seems that I am not overriding the State methods when I create PlayState.

Here’s PlayState.cpp:

#include <SFML/Graphics.hpp>
#include <SFML/Window.hpp>
#include <stdio.h>

#include "PlayState.hpp"

PlayState::PlayState() {
  printf("heyyy\n");
}

void PlayState::start() {
  shape.setRadius(100.f);
  shape.setOrigin(20.0f, 20.0f);
  shape.setFillColor(sf::Color::Green);
}

void PlayState::update() {
  sf::Event event;
  while (game.window.pollEvent(event)) {
    if (event.type == sf::Event::Closed) {
      game.window.close();
      //running = false;
    }
  }

  printf("here\n");
}

void PlayState::render() {
  printf("here\n");
  game.window.clear();
  game.window.draw(shape);
  game.window.display();
}

Any ideas about how I can ‘override’ those methods? Thank you.

EDIT
I had to make State.cpp functions virtual so that they can be overriden.
I also had to define State *currentState as a pointer and create PlayState with “currentState = new PlayState();”.
Also, now I access .update and .draw with ->update() and ->draw().

Answer 1

Two problems. As @McAden said, the functions in State that are to be overridden in PlayState need to be marked virtual. The other problem is that the data member currentState in Game has type State. When you assign an object of type PlayState to it, it gets the State part of the PlayState object, but not the derived parts. This is called “slicing”. To prevent it, make currentState a pointer to State, and when you create that PlayState object, assign its address to the Game object’s currentState.