Pass Member Function Pointers to parent class

Question

I'm working on a Pacman game in C++, but have run into a problem with member function pointers. I have 2 classes, pacman and ghost, that both inherit from Mouvement. In the subclasses, I need to pass a function to a function in Mouvement. However, I can't simply have static functions as then I would need static variables, which would not work.

I have tried passing &this->movingUp which throws the error 'Cannot create a non-constant pointer to member function'

I have tried passing &<ghost or pacman>::movingUp which throws the error "Cannot initialize a parameter of type 'void ()(int)' with an rvalue of type 'void (::)(int)' "

Here's what's relevent: (I cut out most of it, so that you only see what's necessary for this problem)

class cMouvement {
protected:

    int curDirection = -3; // Variables that are used in the 'movingUp, etc' functions.
    int newDirection = -3; // And therefore can't be static


public:

void checkIntersection(void (*function)(int), bool shouldDebug){

    // Whole bunch of 'If's that call the passed function with different arguments

}

And then class pacman and ghost, which are very similar at this point.

class pacman : public cMouvement {

    void movingUp(int type){
        // Blah blah blah
    }

    // movingDown, movingLeft, movingRight... (Removed for the reader's sake)



public:
    /*Constructor function*/

    void move(bool shouldDebug){
        if (curDirection == 0)     {checkIntersection(&movingUp, false);}
        else if (curDirection == 1)     {checkIntersection(&movingRight, false);}
        else if (curDirection == 2)     {checkIntersection(&movingDown, false);}
        else if (curDirection == 3)     {checkIntersection(&movingLeft, false);}
    }

};

score 1 · Accepted Answer · answered Sep 27 '13 at 20:40

1

Why don't you create a virtual function in cMouvement and let checkIntersection to call that virtual function

answered Sep 27 '13 at 20:40

CS Pei

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score 1 · Answer 2 · edited May 23 '17 at 11:59

1

What you want is to supply the signature of a member function, instead of a regular function.

void checkIntersection(void (ghost::*)(int), bool shouldDebug){

See Passing a member function as an argument in C++

If you really need to supply functions from ghost and pacman you need to rethink your strategy. Maybe use virtual functions instead.

edited May 23 '17 at 11:59

Community

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answered Sep 27 '13 at 20:42

PureW

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Yup, I used virtual functions as per John Smith's suggestion. Thanks though! – Matt Reynolds Sep 27 '13 at 21:05

Pass Member Function Pointers to parent class

2 Answers2