Overwriting properties of abstract class - c++

Question

I am defining a class GameState and a class MainMenuGameState. The former is meant to be an abstract class and the latter is inheriting it. But somehow, I am not able to overwrite its properties.
GameState.h
#ifndef _GAME_STATE_H_
#define _GAME_STATE_H_
#include <SDL2/SDL.h>
class GameState {
public:
virtual void loop(Uint32 deltaTime) = 0;
virtual void render() = 0;
virtual void event(SDL_Event * event) = 0;
bool stopRenderPropagation = false;
bool stopLoopPropagation = false;
};
#endif
MainMenuGameState.h
#ifndef _MAIN_MENU_GAME_STATE_H_
#define _MAIN_MENU_GAME_STATE_H_
#include "../Game.h"
class MainMenuGameState : public GameState {
public:
MainMenuGameState(Game * pGame);
void loop(Uint32 deltaTime);
void render();
void event(SDL_Event * event);
bool stopRenderPropagation = true;
bool stopLoopPropagation = true;
private:
Game * game;
int xOffset = 0;
int yOffset = 0;
};
#endif
So after instanciating a MainMenuGameState object, I expected stopRenderPropagation and stopLoopPropagation to be true, but they are false.
I also had no luck overwriting them inside the constructor for some reason.
MainMenuGameState::MainMenuGameState(Game * pGame) {
game = pGame;
xOffset = rand() % 20;
yOffset = rand() % 20;
stopRenderPropagation = true;
stopLoopPropagation = true;
}
After that, they are still true. I don't know weather this is a problem with my constructor or if I misunderstood polymorphism in c++.
The instances of MainMenuGameState get stored in a vector<GameState *>, could this be the problem? I am accessing the properties like this:
if(gameStates.begin() != gameStates.end()) {
std::vector<GameState *>::iterator it = gameStates.end();
do {
--it;
} while(it != gameStates.begin() && (*it)->stopLoopPropagation == false);
while(it != gameStates.end()) {
(*it)->loop(deltaTime);
++it;
}
}
Thank you for your help!

Answer 1

Your derived class is declaring another couple of members with the same name of the members in the base class, thus "hiding" the base ones.
You should accept the initial values for those members in the constructor, or if they are fixed properties of the class that never change you should make them member functions instead like in
class GameState {
public:
...
virtual bool stopRenderPropagation() { return false; }
virtual bool stopLoopPropagation() { return false; }
};
class MainMenuGameState : public GameState {
public:
...
bool stopRenderPropagation() { return true; }
bool stopLoopPropagation() { return true; }
...
};

Answer 2

Inheriting data members (your booleans) does not work in the same way as inheriting and overloading methods. Try putting the bools as protected inherited data members instead (uninitialized), and initialize them in the respective subclass constructors instead.
class MainMenuGameState : public GameState {
public:
MainMenuGameState(Game * pGame);
void loop(Uint32 deltaTime);
void render();
void event(SDL_Event * event);
protected:
bool stopRenderPropagation;
bool stopLoopPropagation;
private:
Game * game;
int xOffset = 0;
int yOffset = 0;
};

Answer 3

You declare new variables in your derived class, which is leading to these problems. Variables that are not private are inherited:
struct A { int x };
struct B : A {}; // has B::x by inheritance
You can just set them in your constructor without redeclaration:
struct A { int x; };
struct B : A { B() : x(1) {} };
Notice that it is usually considered bad practice to declare public variables, it is more common to implement getters and setters instead:
struct A
{
int x() const { return x_; }
int & x() { return x_; }
private:
int x_;
};