[R-pkg-devel] (How) can you use R file i/o within Fortran code in an R package?

[Peter Sørensen]

I have created a fortran interface to a few c functions (fopen, fwrite, fread, fseek) via iso_c_binding that is used in my fortran code. The code can be found here: qgg/bigreml.f90 at master � psoerensen/qgg (github.com)<https://github.com/psoerensen/qgg/blob/master/src/bigreml.f90>
Perhaps this is useful in some way.
Kind regards
Peter
________________________________
Fra: R-package-devel <r-package-devel-bounces using r-project.org> p� vegne af Sokol Serguei <serguei.sokol using gmail.com>
Sendt: 17. februar 2022 10:04
Til: Peter Green <mapjg using bristol.ac.uk>; r-package-devel using r-project.org <r-package-devel using r-project.org>
Emne: Re: [R-pkg-devel] (How) can you use R file i/o within Fortran code in an R package?

Le 16/02/2022 � 16:53, Peter Green a �crit :
> I am developing a package based around several thousand lines of
> legacy Fortran code front-ended with a fairly minimal R function to
> format input and results. In its basic form it is on CRAN, but now I
> want to extend it in a way that will generate copious output over the
> course of the running time of the Fortran code, and I would prefer if
> possible to write this output to (several) files rather than return it
> through arguments to .Fortran.
>
> I have a version using Fortran open, write and close (naturally
> avoiding stderr and stdout), which runs perfectly on several
> platforms, but generates a NOTE in R-hub and Winbuilder:
>
> > * checking compiled code ... NOTE
> > File �Nmix/libs/Nmix.so�:
> >   Found �_gfortran_st_close�, possibly from �close� (Fortran)
> >     Object: �Nmix-sub3z.o�
> >   Found �_gfortran_st_open�, possibly from �open� (Fortran)
> >     Object: �Nmix-sub3z.o�
> >   Found �_gfortran_st_write�, possibly from �write� (Fortran), �print�
> >     (Fortran)
> >     Object: �Nmix-sub3z.o�
> >
> > Compiled code should not call entry points which might terminate R nor
> > write to stdout/stderr instead of to the console, nor use Fortran I/O
> > nor system RNGs.
> that will presumably cause it to fail submission to CRAN, for reasons
> I understand.
>
> Is there a way that I can use R file i/o from within the Fortran code,
> possibly mediated through a C or C++ wrapper? As I am not fluent in
> these languages or all the concepts involved, if it is possible a
> recipe or template would be most appreciated. To fix ideas, (how) can
> I write 100000 integers, separated by white space, to a text file?

I don't have an example in hand, just few pointers which could be useful.
First, how to print from Rcpp
https://teuder.github.io/rcpp4everyone_en/060_printing_massages.html
This example use NumericVector type for an entry parameter which you
won't need. Use just classical C types (double, int, ...) and pointers
on them. You don't need either '//[Rcpp::export]' as you wont call this
function from R but from Fortran.
Second, how to call C from Fortran, e.g.
https://riptutorial.com/fortran/example/7149/calling-c-from-fortran
The fact that your printing function will be in .cpp file does not
matter. C interface will work if you limit your parameters to C types.

Hoping it helps,
Best,
Serguei.

>
> My apologies if this is a well-known question already answered,
> possibly in the negative, but my search through the archives failed to
> find anything. Thank you.
>
> Peter Green
>
>
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