[R] passing char's from C to Fortran (mac os x)

Prof Brian Ripley ripley at stats.ox.ac.uk
Mon Jul 5 16:43:14 CEST 2004

On Mon, 5 Jul 2004, Ingmar Visser wrote:

> Hello All,
> In some package I use a c-routine which calls a fortran routine which
> expects a char-string as input.
> As per the writing R-extensions manual,
> the Fortran routine is declared in C as:
> void F77_NAME (setoptions) (char **option);

That's not in that manual.  It says

 The following table gives the mapping between the modes of R vectors and 
 the types of arguments to a C function or FORTRAN subroutine.

and not between the latter two.

> and then it is calles as follows:
>    char **option; 
>    option = new char*[1];
>    option[0] = new char[256];
>    option[0] = strcpy(option[0],"Iteration Limit = 100");
>    Rprintf(option[0]);
>    F77_CALL (setoptions) (option);
> Unfortunately this does not work, ie the fortran routine setoptions does
> not correctly get the intended character string. Can anyone point me to a
> working example  of passing characters from C to Fortran? Or tell me what's
> wrong in my code above?

It's not C!  (It looks like C++.)  Where did you get the idea that Fortran 
character corresponds to char** in C?  It probably corresponds to char*, 
possibly with a length passed separately.  Since you are probably using 
g77 I expect passing char * from C to Fortran will work, but passing back 
might not.

R is a C program and it manages to pass characters to Fortran in quite a 
few places, such as Lapack.c and loessc.c/loessf.f.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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