Question about pointers

[OffbeatPatriot]

I'm making a game and the game works around a class I call Cyber_State. Every state of the game is a subclass of Cyber_State, for example the title screen you see when you start the game and the actual game.

Every state has a member that is a pointer to a Cyber_State. When a state is created this pointer points to itself, if you want to change states you build the next state and make next_state point to it. For example if you load a game from the main menu you make a new game(subclass of Cyber_State) based on a file and point next_state to it. The main loop then switches the state it works with at the end of the current iteration

Cyber_State.h

#include <Ogre.h>
#include <OIS/OIS.h>
#include <CEGUI/CEGUI.h>
#include <OgreCEGUIRenderer.h>

#include "Cyber_Util.h"
#include "ogreconsole.h"

class Cyber_State
{
	protected:
		Cyber_Kernel *kernel;
		Cyber_State *transition;
	public:
		Cyber_State(Cyber_Kernel *kernel);
		virtual bool frameStarted(const Ogre::FrameEvent& evt);
		virtual bool frameEnded(const Ogre::FrameEvent& evt);
		virtual bool keyPressed(const OIS::KeyEvent &arg);
		virtual bool keyReleased(const OIS::KeyEvent &arg);
		virtual bool mouseMoved(const OIS::MouseEvent &arg);
		virtual bool mousePressed(const OIS::MouseEvent &arg, OIS::MouseButtonID id);
		virtual bool mouseReleased(const OIS::MouseEvent &arg, OIS::MouseButtonID id);
		Cyber_State *next_state();
};

#endif

Cyber_State.cpp

#include "Cyber_State.h"

Cyber_State::Cyber_State(Cyber_Kernel *kernel){this->kernel = kernel; transition = this;}

bool Cyber_State::frameStarted(const Ogre::FrameEvent& evt){return true;}

bool Cyber_State::frameEnded(const Ogre::FrameEvent& evt){return true;}

bool Cyber_State::keyPressed(const OIS::KeyEvent &arg){return true;}

bool Cyber_State::keyReleased(const OIS::KeyEvent &arg){return true;}

bool Cyber_State::mouseMoved(const OIS::MouseEvent &arg){return true;}

bool Cyber_State::mousePressed(const OIS::MouseEvent &arg, OIS::MouseButtonID id){return true;}

bool Cyber_State::mouseReleased(const OIS::MouseEvent &arg, OIS::MouseButtonID id){return true;}

Cyber_State *Cyber_State::next_state(){return transition;}

For an example in my game I run this function at the end of each frame

bool Cyber_Listener::frameEnded(const Ogre::FrameEvent& evt)
{
	state->frameEnded(evt);
	state = state->next_state();
	if(state == NULL)
	{
		running = false;
	}
    return running;
}

My concern is this, what is the life span of a state returned by new_state? If I should delete the old state or it's memory gets freed automatically will the state returned by next_state be destroyed too? Or since Cyber_State only stores a pointer to to the next state will the next state itself be unharmed and accessible while I have a reference to it? While I'm at it does anyone have any links to help me understand memory in c++?

[ArkM]

A pointer value will never been "deleted" automatically. The life span of the state pointer variable does not bear a relation to the life span of the referred object.

In other words, a pointer is a road sign only: "that's a road to Pompeii". May be, the Pompeii was strewn with Vesuvias volcano eruption ashes...

All about pointers for newcomers (and all others ;)):
http://eternallyconfuzzled.com/tuts/languages/jsw_tut_pointers.aspx

[MrSpigot]

My concern is this, what is the life span of a state returned by new_state?

I'm a little confused by that but I assume you meant next_state and not "new state". I don't see you allocating any memory, just moving pointers around, so presumably you allocate the states dynamically somewhere (using new Cyber_State)? If that's the case, the life span of the state is until you delete it. If you delete a state object (A) which contains a pointer to another state object (B) then the pointer in A is freed but object B is still valid and you'd better make sure you still have a pointer to it otherwise it's inaccessible and you have a memory leak.
So remember that any memory you allocate with "new" must be freed with "delete" and you need to care of that. It won't happen automatically.

[mvmalderen]

So remember that any memory you allocate with "new" must be freed with "delete" and you need to care of that. It won't happen automatically.

Unless you're using the <auto_ptr> template, in that case the reserved memory will automatically be freed when the pointer goes out of scope ...

[OffbeatPatriot]

That seems to answer my question well enough. I knew the rule that you free memory made with new with delete but I've seen a lot of examples where this isn't done. They were typically arrays of a few numbers so maybe they didn't care, or does delete basically get called on everything when a program closes?

[MrSpigot]

That seems to answer my question well enough. I knew the rule that you free memory made with new with delete but I've seen a lot of examples where this isn't done. They were typically arrays of a few numbers so maybe they didn't care, or does delete basically get called on everything when a program closes?

It's true that the memory is returned to the OS after the application closes, so in that respect the loss of a small amount of memory during the application isn't going to cause a problem. However, you can see that leaving leaks is bad practice for a whole host of reasons. The class containing your leak maybe reused elsewhere in other apps in such a way that a large leak occurs. You may change the operation slightly which causes a single one-time leak to become a cumulative leak.
Basically, don't leave the OS to clean up for you, one day you'll write code which needs to work, and it'll bite you in the bum.