🚀 go-pugleaf

In article <1994May5.075259.12146@reks.uia.ac.be> rgeens@wins.uia.ac.be (Ronald.Geens) writes:
>In article <CpAn8x.5I1@news.cis.umn.edu>, ianhogg@milli.cs.umn.edu (Ian J Hogg) writes:
>
>|> >|> 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.
>|> >
>|> >Actually the function does not have to have "extern C" linkage.  It just
>|> >can't be a non-static member function.
>|> >
>|> 
>|> Actually, the callback function should have "C" linkage.  I have used a 
>|> compiler that passed arguments differently  for C linkage and C++ linkage.
>|> So, if I had a free standing function with C++ linkage and used it as a 
>|> callback function, the parameters would be messed up.  This is not an issue 
>|> with most compilers but be aware it could be.  
>|> 
>|> Can anyone guess the compiler in question?
>
>I really don't have a clue! I thought the discussoin was purely theoretical !
>
>If you have worked with such a compiler, how did you use member functions as callbacks ? Or is it just not possible on such compilers ?

I wasn't even trying to use member functions as callbacks becuase you need a
normal function as glue.  Once I figured out the problem I just declared all
my callbacks like this:

extern "C" void my_callback(Widget w, XtPointer client_data, XtPointer cbs)
{
   /* do stuff here */
}

Anytime you are passing a pointer to a function as a parameter to a function
with "C" linkage, the passed function pointer should be declared with
"C" linkage.
--
===============================================================================
Ian Hogg						ianhogg@cs.umn.edu
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