🚀 go-pugleaf

Paul Durbin (pauld@verdix.com) wrote:
: I attempt to use a member function as callback but all three arguments (to the
: callback) are garbage. If I make it a friend then the arguments are correct,
: but then I can't get to the class data, without reference thru an instance of
: the class and I don't want the data to be static.

: So, what is causing this problem? 

Motif is based on C, not C++.  You have to use "extern C" linkage for any of
your callbacks.  You can't register any C++ function directly.  You have to
write a plain C front end for anything you want to have callbacked.


: Could I possibly use the *this pointer as
: the client_data to the callback, then cast to the appropriate class?

Yes.  That's how I do it below.  Write functions like this:


extern "C" void ImageExposeCB(Widget DrawArea,
			      XtPointer Image,
			      XtPointer cbs)
{  
  XmDrawingAreaCallbackStruct *x = (XmDrawingAreaCallbackStruct *)cbs;
  XExposeEvent *e = (XExposeEvent *)(x->event);
  (Image *)Image->Expose(e);

}


Here (Image) is my own C++ object.  What I'm really trying to do, is get my
Image->Expose(e) function to be used as a callback.  (cbs) is a callback
structure provided by Motif.


Cheers,
Brandon

--
Brandon Van Every             "No more LaunchPAD .Sigs!  HA HA HA HA HA HA!!!"
brandon@uncvx2.oit.unc.edu