SDL2 Joystick hot-plugging example

joypad.cpp

#define MAX_CONTROLLERS 4

class JoypadController {
public:
	JoypadController() : m_is_connected(false), m_gamepad(0), m_instance_id(-1), m_haptic(0) {}

	int JoypadController::processEvent(const SDL_Event& event);
private:
	SDL_GameController *m_gamepad;
	SDL_Haptic *m_haptic;
	SDL_JoystickID m_instance_id;
	bool m_is_connected;

	static JoypadController m_controllers[MAX_CONTROLLERS];
	static int GetControllerIndex(SDL_JoystickID instance);

	void Open(int device);
	void Close();

}

// Opens the joystick controller
void JoypadController::Open(int device)
{
	m_gamepad = SDL_GameControllerOpen(device);
	SDL_Joystick *j = SDL_GameControllerGetJoystick(m_gamepad);
	m_instance_id = SDL_JoystickInstanceID(j);
	is_connected = true;
	if (SDL_JoystickIsHaptic(j)) {
		m_haptic = SDL_HapticOpenFromJoystick(j);
		printf("Haptic Effects: %d\n", SDL_HapticNumEffects(m_haptic));
		printf("Haptic Query: %x\n", SDL_HapticQuery(m_haptic));
		if (SDL_HapticRumbleSupported(m_haptic)) {
			if (SDL_HapticRumbleInit(m_haptic) != 0) {
				printf("Haptic Rumble Init: %s\n", SDL_GetError());
				SDL_HapticClose(m_haptic);
				m_haptic = 0;
			}
		} else {
			SDL_HapticClose(m_haptic);
			m_haptic = 0;
		}
	}
}

void JoypadController::Close()
{
	if (is_connected) {
		is_connected = false;
		if (haptic) {
			SDL_HapticClose(haptic);
			haptic = 0;
		}
		SDL_GameControllerClose(gamepad);
		gamepad = 0;
	}
}

int JoypadController::GetControllerIndex(SDL_JoystickID instance)
{
	for (int i = 0; i < MAX_CONTROLLERS; ++i)
	{
		if (ms_controllers[i].m_is_connected &&  ms_controllers[i].m_instance_id == instance) {
			return i;
		}
	}
	return -1;
}

int JoypadController::processEvent(const SDL_Event& event)
{
	switch (event.type) {
		case SDL_CONTROLLERAXISMOTION: {
			// handle axis motion
			break;
		}
		case SDL_CONTROLLERBUTTONDOWN:
		case SDL_CONTROLLERBUTTONUP: {
			// handle button up/down
			break;
		}
		case SDL_CONTROLLERDEVICEADDED: {
			if (event.cdevice.which < MAX_CONTROLLERS ) {
				JoypadController& jc = s_controllers[event.cdevice.which];
				jc.Open(event.cdevice.which);
			}
			break;
		}
		case SDL_CONTROLLERDEVICEREMOVED: {
			int cIndex = GetControllerIndex(event.cdevice.which);
			if (cIndex < 0) return 0; // unknown controller?
			JoypadController& jc = ms_controllers[cIndex];
			jc.Close();
			break;
		}
	}
	return 0;
}

Thank you, this post was the only helpful discussion of these two events on the whole internet! (SDL_CONTROLLERDEVICEADDED and SDL_CONTROLLERDEVICEREMOVED)

Thanks, that helped me a lot with this:
https://github.com/slajerek/MTEngineSDL/blob/master/src/Engine/Core/GAM_GamePads.cpp