Calling C from Fortran

I actually deleted a part of my reply, dealing with exactly that. Sorry!
You need to declare the C wrapper to take a pointer to a double ("double
*") rather than a double. C passes by value whereas Fortran passes by
reference; in C you get this effect by passing a pointer to the value
(which is also a value). So you want

double F77_SUB(mygammafn)(double *x) { return gammafn(x); }

That should work; if not let me know and I'll look more carefully at
Fortran <-> C conventions.

Reid Huntsinger

-----Original Message-----
From: Gilles GUILLOT [mailto:gilles.guillot at inapg.inra.fr]
Sent: Wednesday, June 15, 2005 3:50 AM
To: Huntsinger, Reid
Subject: Re: [Rd] Calling C from Fortran


Thanks Reid!
And now if I want to call a C function with arguments,
e.g. to compute the gamma function at x,
my C wrapper is:

#include <R.h>
#include <Rmath.h>
void F77_SUB(rndstart)(void) { GetRNGstate(); }
void F77_SUB(rndend)(void) { PutRNGstate(); }
double F77_SUB(normrnd)(void) { return norm_rand(); }
double F77_SUB(mygammafn)(double x) { return gammafn(x); }

And my Fortran is:
    subroutine testit()
     implicit none
     double precision normrnd, x, y, mygammafn
      call rndstart()
      x = dabs(normrnd())
      write(*,*) 'x=',x
      call rndend()

      y = mygammafn(x)
      write(*,*) 'y=',y
      end

And it does not work, all calls of testit return the same y value.
What is incorrect in my files ?


Gilles





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