Difficulty accessing a member of a class from a list

[JS Lemming]

So I have a stageObject class...

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#ifndef STAGEOBJECT_H
#define STAGEOBJECT_H

#include <GL/gl.h>

class stageObject
{
	public:
		GLfloat x, y;
		//sprites
		stageObject();
		virtual void update()=0;
		virtual void draw()=0;

	private:
		// add your private declarations
};

#endif // STAGEOBJECT_H

And just fyi, a hector class with inherits from it...

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#ifndef HECTOR_H
#define HECTOR_H


#include "stageobject.h"

class hector: public stageObject
{
	public:
		int test;
		hector();
		virtual ~hector();
		void update();
		void draw();

	private:
		// add your private declarations
};

#endif // HECTOR_H

Now, I have a stage class that contains a list and list interator for stageObjects...

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#ifndef STAGE_H
#define STAGE_H

#include <list>
#include "stageobject.h"

class stage
{
	public:
		std::list<stageObject*> stageObjects;
		std::list<stageObject*>::iterator i;

		stage();

	private:
		// add your private declarations
};

#endif // STAGE_H

When that class is constructed it makes a hector and puts it in the list...

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#include "stage.h"
#include "hector.h"

stage::stage()
{
	hector *dude = new hector;
	stageObjects.push_back(dude);
}

EDIT: ^^ btw, does anyone know of a nicer way of doing that so it's all on one line... and not needing of dude?

Now, in my main I make a new stage and try to iterate through the list and assign a value to one of the stageObject's member variables...

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		stage *gameStage = new stage;
		//try to interate thru that list that stage has

		for(gameStage->i=gameStage->stageObjects.begin(); gameStage->i != gameStage->stageObjects.end(); ++gameStage->i)
		{
			gameStage->i->x = 44;
		}

It iterates through the list just fine. However, the act of trying to access that x member gives me this error:

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main.cpp:196: error: request for member ‘x’ in ‘* gameStage->stage::i.std::_List_iterator<_Tp>::operator-> [with _Tp = stageObject*]()’, which is of non-class type ‘stageObject*’

I have a feeling it's something simple I'm missing... Any help would be appreciated.

[Falco Girgis]

Hrm, I haven't really messed with std::iterator and std::list before, but it looks like an inheritance issue to me. Looks like the Hector object isn't polymorphing back into a stage object when you're referencing it. Have you tried to explicitly typecast it like this?

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(stageObject *)gameStage->i->x = 44;

[JS Lemming]

Yes, it yields an identical error.

[Falco Girgis]

I've been staring at this for like 20 minutes, I'm starting to get pissed. I don't see anything wrong. I even learned C++ lists and iterators just to look at this more.

This won't be a neat or pretty fix, but I'm curious if you can do this:

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stageObject *temp = gameStage->i;
temp->x = 44;

Oh, and my typecast above was both pointless and stupid. Typecasting what, a GLFloat to a stageObject pointer? XD

[M_D_K]

So I have a stageObject class...

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#include "stage.h"
#include "hector.h"

stage::stage()
{
	hector *dude = new hector;
	stageObjects.push_back(dude);
}

EDIT: ^^ btw, does anyone know of a nicer way of doing that so it's all on one line... and not needing of dude?

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stageObjects.push_back(new hector);//this should work ;)

to access the iterator do this

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(*i)->SomeFunction();

[Falco Girgis]

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(*i)->SomeFunction();

Oh my god, you have to be kidding me.

edit: I see what you did there. 0_o

[M_D_K]

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(*i)->SomeFunction();

Oh my god, you have to be kidding me.

[JS Lemming]

to access the iterator do this

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(*i)->SomeFunction();

I tried that earlier and got some new error.

I did...

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gameStage->(*i)->x = 44;

and got this...

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main.cpp:196: error: expected unqualified-id before ‘(’ token
main.cpp:196: error: ‘i’ was not declared in this scope

Or am I missing what you meant?

Oh, and my typecast above was both pointless and stupid. Typecasting what, a GLFloat to a stageObject pointer? XD

haha I did it too so we're both retards.

EDIT: oops, I missed your idea Gyro. I'll try that in a min.

[M_D_K]

try removing the "(" and ")"(i'm to lazy to try and spell them)

so:

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gameStage->*i->x = 44;

[JS Lemming]

Removing the () just results in the second error: ‘i’ was not declared in this scope

[M_D_K]

well Why don't you just go

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      for(uint i  = 0;i < gameStage->stageObjects.size(); ++i)
      {
         gameStage->stageObjects[i]->x = 44;
      }

[Falco Girgis]

Okay, serious question.

What the fuck does an iterator return? An integer? The indirection operator is overloaded to return a pointer to the current object?

[M_D_K]

An iterator acts as an index for the list. When dereferenced it acts as the object at the point of the list its pointing to.

I think...

[JS Lemming]

well Why don't you just go

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      for(uint i  = 0;i < gameStage->stageObjects.size(); ++i)
      {
         gameStage->stageObjects[i]->x = 44;
      }

An array? That's soo..... I dunno.... I've always had trouble with these dang lists in the past and I'm determined to finally get them working.


EDIT! Falco you are my hero! I tried a slight alteration of your idea and got it working.

I had to do...

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			stageObject *temp = *gameStage->i;
			temp->x = 44;

Now all I need to know is why the hell do I have to do that. It's essentially the same as in above posts but expanded out. Makes me think the syntax for what I was trying is more complicated than what I tried.


Moe Edit: Aight. Figured it out. It was just tricky parenthesis placement. Thanks guys.

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(*gameStage->i)->x =44;

[M_D_K]

An array? That's soo..... I dunno.... I've always had trouble with these dang lists in the past and I'm determined to finally get them working.

Not really you'd still be using an std::list just accessing it like an array.

Moe Edit: Aight. Figured it out. It was just tricky parenthesis placement. Thanks guys.

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(*gameStage->i)->x =44;

I can't believe I missed that...my leetness is fading