Question

Possible Duplicate:
How can I pass a class member function as a callback?

I have two classes A and B

class A
{
public:
   void SetHandler(void (*p)(OMX_BUFFERHEADERTYPE*)){ Handler = p; };
private:
  void (*Handler)(OMX_BUFFERHEADERTYPE*);
}

and

in B I have a function

void B::handler(OMX_BUFFERHEADERTYPE* p){};

now when (from B) I call

inst_a.SetHandler(&B::handler);

i get the following error:

B.cpp:740:69: error: no matching function for call to ‘A::SetHandler(void (COMXVideo::*)(OMX_BUFFERHEADERTYPE*))’
B.cpp:740:69: note: candidate is:
A.h:161:8: note: void A::SetHandler(void (*)(OMX_BUFFERHEADERTYPE*))
A.h:161:8: note:   no known conversion for argument 1 from ‘void (B::*)(OMX_BUFFERHEADERTYPE*)’ to ‘void (*)(OMX_BUFFERHEADERTYPE*)’

what am I doing wrong?

Best Regards

Answer 1

&B::handler is not a function pointer, but a pointer to member function. If B::handler doesn’t need members of B, you can define it static. Then SetHandler(&B::handler) will work.

If you must have a pointer to member function, you can define it as

void (B::*Handler)(OMX_BUFFERHEADERTYPE*);

when you call such a member function, you need a pointer to an object as well

(inst_b->*Handler)(omxbuffer);

or with a reference

(inst_b.*Handler)(omxbuffer);