Pointer problem

This is a discussion on Pointer problem within the C++ Programming forums, part of the General Programming Boards category; Hi Im having a few problems with pointers and was wondering whether anyone can point me in the right direction. ...

  1. #1
    Registered User ventolin's Avatar
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    Question Pointer problem

    Hi Im having a few problems with pointers and was wondering whether anyone can point me in the right direction.

    I have the following code:

    Code:
    class LatticeNode {
    
    	public:
    		int num;
    		Cell c;
    
    		LatticeNode *next;
    		LatticeNode *prev;
    	
    		Cell* getCell() { return c; }
    		LatticeNode(Cell *c);
    };
    This forms part of a larger class which forms a simple linked list:

    Code:
    template< class T, int size> class Lattice 
    {
    	public:
    
    		Lattice();
    		~Lattice();
    
    		LatticeNode *getCurrent() { return current; }
    
    		void polarise();
    
    	private:
    
    		LatticeNode* current;
    };
    Now im trying to use the getCell method from LatticeNode to return the object Cell c from the LatticeNode object, like so:

    Code:
    current->getCell()->signal(dt);
    Where signal(dt) is a function in the object Cell. If i call it like this then it crashes, and i dont understand why its causing this..

    Im not sure on the return type for the getCell function .. do i return just c or a reference to &c?

    I believe the Cell object is being created when i call the LatticeNode constructor, although am i pointing to something which doesnt exist??

    Any help, suggestions welcomed!

  2. #2
    & the hat of GPL slaying Thantos's Avatar
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    Quote Originally Posted by ventolin
    Code:
    class LatticeNode {
    
    	public:
    		int num;
    		Cell c;
    
    		LatticeNode *next;
    		LatticeNode *prev;
    	
    		Cell* getCell() { return c; }
    		LatticeNode(Cell *c);
    };
    You are saying getCell returns a pointer to a cell but you are trying to return the cell itself. Possible changes:
    Code:
    Cell& getCell { return c; }
    Cell* getCell { return &c; }
    Now the top one returns a reference to the cell so you would
    Code:
    current->getCell().signal(dt);
    With the bottom one it returns a pointer so you wouldn't need to change it. I'm surprised your compiler didn't warn about this though.

  3. #3
    Registered User ventolin's Avatar
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    Is there no way to do it without using a reference to the object? or can i still use the pointer method? If i use the reference style i need to major changes to all of my code... and my compiler (VC++) complains if i have the two methods...

  4. #4
    & the hat of GPL slaying Thantos's Avatar
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    No you can use the pointer method. Was just giving you options

  5. #5
    Registered User ventolin's Avatar
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    Ok thanks ill take a look at this.. cheers!

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