Re: [Rd] Calling C from Fortran

From: Huntsinger, Reid <reid_huntsinger_at_merck.com>
Date: Tue 14 Jun 2005 - 17:32:21 GMT


The C wrappers are there to align the linking conventions expected by the Fortran compiler (usually subroutine/function foo has its entry point in the object file indicated by a symbol foo_, but it depends on the platform) to that of the C compiler. (The C compiler just uses the function name.) The wrappers give C functions named whatever is appropriate (eg "foo_") to get an entry point that "call foo" will trigger linking to.

Calling the Fortran subroutine from R is via .Fortran() after doing a dyn.load() of the shared object file. Creating the shared object should just be a matter of R CMD SHLIB file1.c file2.f but I've never tried using Fortran and C together. Take a look at the magic built in to the R CMD SHLIB and R CMD COMPILE commands, and at some of the packages that come with R (I just do a "find" for "*.f" in the src tree) if you need examples, eg. src/library/stats.

Reid Huntsinger

-----Original Message-----
From: r-devel-bounces@r-project.org [mailto:r-devel-bounces@r-project.org] On Behalf Of Gilles GUILLOT
Sent: Tuesday, June 14, 2005 1:05 PM
To: R-devel@stat.math.ethz.ch
Subject: [Rd] Calling C from Fortran

I would like to call C routines from Fortran under linux as suggested in section 5.6 of
the "Writing R extensions" documentation.

I'm familiar with Fortran but not with C. I understand the example provided in Fortran:

subroutine testit()
double precision normrnd, x
call rndstart()

x = normrnd()
call dblepr("X was", 5, x, 1)
call rndend()

end

but I don't understand the purpose of this C wrapper: #include <R.h>
 void F77_SUB(rndstart)(void) { GetRNGstate(); }  void F77_SUB(rndend)(void) { PutRNGstate(); }  double F77_SUB(normrnd)(void) { return norm_rand(); }

neither how I should compile it.

Could anyone explain how I should compile and link the C and Fortran files above, and call the Fortran subroutine from R.

Thanks,

Gilles



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