An Array of Function Pointers in C++

Question

I'm trying to figure out on how can I make an array of pointers to functions that are inside a class. Where an element in an array represents a unique function.

Tiles.h code:

class tiles: public box
{
    public:
        void north2east(float trans_x, float trans_y);
        void north2west(float trans_x, float trans_y);
        void south2east(float trans_x, float trans_y);
        void south2west(float trans_x, float trans_y);
};

Tiles.cpp code:

void tiles::north2east(float trans_x, float trans_y); { }
void tiles::north2west(float trans_x, float trans_y); { }
void tiles::south2east(float trans_x, float trans_y); { }
void tiles::south2west(float trans_x, float trans_y); { }

I've heard that you can do it by adding the following in the Tiles.cpp file:

typedef void (*FUNC_ARRAY) (float trans_x, float trans_y);
FUNC_ARRAY functions[] = {
    tiles::north2east,
    tiles::north2west,
    tiles::south2east,
    tiles::south2west
}

But this gives me the following error:

a value of type "void (tiles::*)(float trans_x, float trans_y)" cannot be used to initialize an entity of type "FUNC_ARRAY"

Tips and suggestions on solving the code are welcome!

That typedef can only be used for ordinary functions or static member functions. — Barmar
– Barmar, Commented Apr 9, 2015 at 9:17
See warplife.com/tips/code/c++/member-pointers.html for how to declare pointers to member functions. — Barmar
– Barmar, Commented Apr 9, 2015 at 9:17
You assign pointer to methods and those aren't pointers to functions as you cannot invoke them without an object instance. — W.F.
– W.F., Commented Apr 9, 2015 at 9:18

sh03 · Accepted Answer · 2015-04-09 09:18:07Z

5

Just change your typedef to:

typedef void (tiles::*FUNC_ARRAY) (float trans_x, float trans_y);
//            ^^^^^^^

Your current typedef can only be used for regular functions and static member functions. What you need there is a pointer to a member function.

answered Apr 9, 2015 at 9:18

sh03

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1 Comment

W.F. Over a year ago

@VesmirPendel have in mind that now you will be able to invoke those method only on objects, like: tiles t; (t.*function[1])(1.0, 1.0); or tiles *t = new t; (t->*function[1])(1.0, 1.0);

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