[Rd] capturing value of C or Fortran function

Hin-Tak Leung hin-tak.leung at cimr.cam.ac.uk
Wed Dec 13 19:59:42 CET 2006

Well, fortran subroutines don't really have return values (versus 
fortran functions, which do - as far as I know that's the only 
difference between fortran subroutines and functions).

There is also a somewhat sticky matter, of C routines that returns
fairly complex types, like pointers, strings... and likewise, fortran
functions can return rather complex things, like matrices, etc.
It is going to be difficult to do a one-size-fit-all solution.

So all you are trying to cater for, is a rather small subset of 
C/fortran functions which returns a single int or a single double?

(anything to do with arrays you'll need to "smuggle" the array size
out the old-fashion way via argument pointers).

Harris A. Jaffee wrote:
> Re: src/main/dotcode.c:do_dotCode()
> The value, if there is one, of a function called by .C or .Fortran is not
> captured, so one needs a wrapper.  To avoid that, the user would have to
> declare that there is a value, specify its type, and supply an R variable
> to hold the value.  Presumably, all of these could be combined in a new
> "VALUE=var" parameter.  Then do_dotCode could arrange the correct type of
> C variable to receive the value (for every one of the 66 possible instances
> of the call), and then transfer that value to 'var'.  It seems doable with
> a strong enough macro, if a bit complicated.  Or one could say VALUE=<type>
> and get the value as a new, (n+1)_th element of the current list value.
> Of course, existing code naming an argument with "VALUE" would break, so a
> completely new interface, perhaps .C.function(), .Fortran.function(), would
> be required to avoid that.
> Has this facility been ruled out?
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