The problem is that I need to register the C function with a codebase
I don't control.  I need to call a function like this in C:

  int RubyCallback(void *thing) {...}

  DefineFunction("ruby-callback", 'd', (int (*)(void)) RubyCallback,
"RubyCallback");

The leading inputs are not important for the example but if you look
at the latter arguments you can see I need both a pointer to the
callback function and the name of the function.  I think the FFI
callback provides a function pointer but not a name, right?  Is there
a way I can name the callback?

I'm ok with manually maintaining my calls to the C api.  Do you have
suggestions about how I can use it in this context? Thanks.

==== FYI

This is the signature of the DefineFunction method.

  int      DefineFunction(functionName,functionType,
functionPointer,actualFunctionName);
  char    *functionName, functionType, *actualFunctionName;
  int    (*functionPointer)();

And if it helps, the version of the passing OS X is 10.5.8.





On Dec 9, 12:04 am, Wayne Meissner <wmeiss...@gmail.com> wrote:

> Really, don't use the C api - it will break at some point, since it is
> not intended in any way to be a public api.
>
> Use a FFI callback to call from C to ruby.
>
> http://wiki.github.com/ffi/ffi/exampleshas a callback example, as
> doeshttp://wiki.github.com/ffi/ffi/windows-examples
>
> 2009/12/9 Simon Chiang <simon.a.chi...@gmail.com>:
>

> > I'm building a callback to ruby from an extension and I would like to
> > pass back pointers much like an attached function that returns
> > a :pointer.  Basically something like this:

>

> >  int RubyCallback(void *thing)
> >  {
> >    VALUE ffi_pointer = rbffi_Pointer_NewInstance(thing);
> >    VALUE ruby_module = rb_const_get(rb_cObject, rb_intern
> > ("SomeModule"));
> >    VALUE ruby_result = rb_funcall(ruby_module, rb_intern("callback"),
> > 1, ffi_pointer);

>

> >    long result = FIX2INT(ruby_result);
> >    return(result);
> >  }

>

> > And then in ruby:

>

> >  module SomeModule
> >    module_function

>

> >    def callback(ptr)
> >       ptr.inspect         # => shows this to be an FFI::Pointer
> >    end
> >  end

>

> > A method like this works on OS X with ffi-0.5.0 (pre snow-lepoard,
> > I'll get the version if necessary) but results in a segfault on snow
> > leopard 10.6.2.  The segfault is triggered upon inspect.  I don't know
> > how FFI works... I really only got this working by taking a guess at
> > what rbffi_Pointer_NewInstance does.  Any ideas what's going wrong on
> > 10.6.2 and/or how I can do this better?

>
>