Re: extern "C", C++, and GTK+ callbacks.

[Murray Cumming <murrayc murrayc com>]

Yes, I think it's correct. It's just difficult to correct it:
http://bugzilla.gnome.org/show_bug.cgi?id=164852

On Tue, 2005-01-25 at 12:18 -0600, Robert Zeh wrote:
> Murray,
> 
> I believe you don't have much choice in the matter.  We've been bitten
> by the same problem, and we came up with the same solution.
> 
> When gcc accepts the code, it is is silently converting an pointer to
> function with C linkage to a pointer to function with C++ linkage. 
> There is no reason, from a portability and standards point of view,
> for the two to be the same.
> 
> As hard as it is for me to say, I believe that the SunPro compiler's
> behavior is, in this case, correct.
> 
> Robert Zeh
> http://home.earthlink.net/~rzeh
> 
> Murray Cumming wrote:
> 
> >Some compilers [1], correctly complain when we use a static member
> >function as a GTK+ callback. GTK+ expects (and declares) an "extern C"
> >pointer-to-function, but our static member methods are not declared as
> >"extern C".
> >
> >Unfortunately, it seems that static member methods can never be extern
> >"C". g++ does not allow anything like this:
> >
> >class something
> >{
> >public:
> >  extern "C" void function_one(); 
> >
> >  extern "C"
> >  {
> >    void function_one();
> >  }
> >}
> >
> >
> >So we have to move the callbacks outside of the class, and declare them
> >as friend functions so that they can access the class:
> >
> >extern "C"
> >{
> >  void Something_function_one();
> >}
> >
> >class something
> >{
> >public:
> >  friend void function_one();
> >
> >protected:
> >  void something_protected();
> >}
> >
> >void Something_function_one()
> >{
> >  //Get something somehow.
> >  //Use it:
> >  something.something_protected();
> >}
> > 
> >
> >This is annoying. Does anyone have a simpler suggestion?
> >
> >
> >[1] SUN Forte issues warnings. MipsPro issues errors, stopping the
> >compilation.
> >
> >  
> >
> 
-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com
www.openismus.com