vtable offset 0

[attaboy]

What exactly does this mean?
function=&virtual table offset 0

(The function is a static member function pointer)

This is a message from gdb. I'm trying to figure out what's going wrong in my code. Keep getting SIGSEGV.

[guestgulkan]

have you actually defined the function that this pointer will be pointing to??

[attaboy]

Yes they are defined as virtual functions.

[guestgulkan]

This is where I say 'show the code'

[attaboy]

It goes something like this:

class Dummy { };
class EventManager { //Singleton
     private:
          static void (EventManager::*someFunc)(void); // This of course is initialized to be 0
          /.../
          static void someEvent(void) { // This HAS to be static!
              EventManager &em = instance() // Singleton!
              (em.*someFunc)(); // SIGSEGV
          }
     public: 
          void setFunction(void (Dummy::*function)()) {
               /.../
               someFunc = reinterpret_cast<void (EventManager::*)(void)>(function);
          }
}

class Main : public EventManager {
    /.../
         Main : EventManager() { setFunction(void (Dummy::*)()>(&Main::function)) }
    protected:
         virtual void function(void) { }
    /.../
};

Now the final user should be able to implement this as

class MyMain : Main {
     /.../
     protected:
          virtual void function() { //put sth in here }
     /.../
}

Thank you for the fast answers so far ;-)

[guestgulkan]

Is this safe casting??
I'm going off to re-check the blurb on reinterpret_cast - but this doesn't look right to me.

I think it goes like this:

pointer to class member functions are not actually address, like normal pointers, they are actually
indexes.
So line 19 when you do this:
Main : EventManager() { setFunction(void (Dummy::*)()>(&Main::function)) } you are getting the index of Main::function which is a virtual function
This is passed to Line 11:

          void setFunction(void (Dummy::*function)()) {
               /.../
               someFunc = reinterpret_cast<void (EventManager::*)(void)>(function);
          }

But Event Manager has no virtual members - so the index into the virtual function table is invalid.

Well something like that anyway I think :-)

[attaboy]

Thank you!! I still get the SIGSEGV but at least the vtable problem seems to be fixed...

[RedX]

You cannot call a member function without specifying which object the member function belongs to.

Read up on this. This should clarify you on your problem.
http://www.parashift.com/c++-faq-lite/pointers-to-members.html

[attaboy]

Thanks a lot :-)