Thread: Templates and type casts

  1. #1
    Registered User ventolin's Avatar
    Join Date
    Jan 2004

    Templates and type casts

    Hi, i have a simple compile time error which i cant get rid of, and was wondering if anyone can help me out.

    pcp2\lattice.cpp(15) : error C2440: '=' : cannot convert from 'class LatticeNode<T> *' to 'class LatticeNode<class Juxtacrine> *'
    Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
    c:\program files\microsoft visual studio\vc98\include\xmemory(59) : while compiling class-template member function '__thiscall Lattice<class Juxtacrine,500>::~Lattice<class Juxtacrine,500>(void)'
    Error executing cl.exe.

    PCP2.exe - 1 error(s), 0 warning(s)
    Ok thats the error and heres the code its related to.

    template <class T> class LatticeNode {
    		int num;
    		T t;
    		//next/prev nodes
    		LatticeNode *next;
    		LatticeNode *prev;
    		//default constructor
    template< class T, int size> class Lattice 
    		int dimensions();
    		void remainder_cells();
    		void set_links();
    		void add(int i, int j);
    		void remove(int i, int j);
    		int width, height;
    		LatticeNode* current;
    		LatticeNode* head;
    		LatticeNode* tail;
    		void init();
    template <class T, int size> Lattice<T,size>::~Lattice()
    	LatticeNode *save;
    	for (current = head; current != tail; current = save) {
    	    save = current->next;
    		delete current;
    	delete tail;
    The code in red is where i guess its referring to.

    Im not sure how to re-cast the 'save' variable into what the compiler suggests.. any ideas on how to solve this?

  2. #2
    Registered User
    Join Date
    Apr 2002
    In your Lattice class you need to specify template parameters to your LatticeNode pointers. Like so:

    LatticeNode<T>* current;
    LatticeNode<T>* head;
    LatticeNode<T>* tail;
    And then in your destructor..

    LatticeNode<T> *save;
    Also you might want to make sure you have a constructor body.
    "...the results are undefined, and we all know what "undefined" means: it means it works during development, it works during testing, and it blows up in your most important customers' faces." --Scott Meyers

  3. #3
    Registered User ventolin's Avatar
    Join Date
    Jan 2004
    Excellent thanks, i completely missed that !

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