pointers to pointers and functions

[globalenemy]

Greetings,

I'm trying to target a variable that is not declared in my scope. I think this should be realized by pointers. But somehow i can't get it to work properly.

I have a Grid of Points and a Walker. The Walker can go from Point to Point, but to do that, he needs to know on wich grid he is. In my first attempt I allways told him on wich grid he is, when i told him to go somewhere.
GoTo(&grid, goal);

This didn't look so nice. So now I want to store the pointer to the Grid inside the Walker. So I only need to tell him the Grid on creation.

class CWalker {
	private:
		enum { POINT_FREE = 0, POINT_BLOCKED = 1, POINT_WALKED = 2 };

	public:
    	CWalker();
    	CWalker(CGridXP *g, int pos);

    	CGridXP **grid;
    	int position;

    	void Reset();
    	void GoTo(int goal);
};

CWalker::CWalker(CGridXP *g,int p) {
	grid = &g;
    position = p;
}

void CWalker::Reset() {
    for(int i = 0; i < grid->getSize(); i++) {
        if (i == position) grid->setPointType(i, POINT_WALKED);
        else if (!(grid->getPointType(i) == POINT_BLOCKED)) grid->setPointType(i, POINT_FREE);
    }
}

This looks right doesn't it? Well g++ doesn't think so:

System/CWalker.cpp:11:30: error: request for member ‘getSize’ in ‘*((CWalker*)this)->CWalker::grid’,
 which is of pointer type ‘CGridXP*’ (maybe you meant to use ‘->’ ?)
     for(int i = 0; i < grid->getSize(); i++) {

this message references to line 22 of the code I quoted above.

I really don't know what to do with this. Maybe I want to use '->'? I'm allready using that, wtf?

Please help me out! :(

[MiiNiPaa]

CGridXP **grid;

Why do you need a double pointer?

grid->getSize();

grid->would eliminate one level of indirection. You still have one more.

[hyperfine]

grid->getSize();
grid->would eliminate one level of indirection. You still have one more.

MiiNiPaa, how would this look? *grid->getSize()?

[globalenemy]

I just learned about pointers. And I used a 'double pointer' (as you call it) because I thought it would be the right way to realize my plan.

well, thank you MiiNiPaa. with the following changes everything works properly:

class CWalker {
	private:
		enum { POINT_FREE = 0, POINT_BLOCKED = 1, POINT_WALKED = 2 };

	public:
    	CWalker();
    	CWalker(CGridXP *g, int pos);

    	CGridXP *grid;    //updated
    	int position;

    	void Reset();
    	void GoTo(int goal);
};

CWalker::CWalker(CGridXP *g,int p) {
	grid = g;    //updated
    position = p;
}

[MiiNiPaa]

(*grid)->getSize(); ← operator precendence
Also you can use
(**grid).getSize(); 
Or obscure.
grid[0]->getSize(); and grid[0][0].getSize();

Or you can throw out double pointer. Why do you need it? It is error prone and should be avoided unless absolutely nessesary.
To illustrate: you had a bug in your code, which leads to value of your pointer to be overwritten. So your program will not work (reliably)

EDIT: took too long to write answer. Now it looks better.