[R] dll problem with C++ function

[Peter Langfelder]

Just a shot in the dark... Do you properly close the input/output
files at the end of your function? If not and the file remains open,
it may throw an error upon new attempt to read it. It is possible that
dyn.unload, among other things, closes all open connections and hence
upon re-load everything works fine.

Peter

On Wed, Nov 3, 2010 at 6:47 AM, Carsten Dormann <carsten.dormann at ufz.de> wrote:
> Dear fellow R-users,
>
> I have the problem of being unable to repeatedly use a C++-function within R
> unless by dyn.unloading/dyn.loading it after each .C call.
>
> The C++-code (too large to attach) compiles without problem using R CMD
> SHLIB. It loads (using dyn.load("myfun.so")) and executes (via .C(myfun,
> ...) ) properly. The function returns no object, only reads files from disk,
> performs calculations and later writes a file to disk.
> When I now use the same line of code again to re-run the analysis (again via
> .C), I get an error message claiming a malformed input file. This seemingly
> malformed input file is absolutely correct.
>
> When I now use dyn.unload("myfun.so") and then again dyn.load("myfun.so"), I
> can use it as before.
>
> I have absolutely no clue what is going on here. The C++-function returns a
> 1 if run correctly and 0 otherwise. The stand-alone version works fine. My
> feeling is that R cannot deallocate the memory or somehow doesn't "grasp"
> that the dll should be freed after running.
>
> My impression is there is a very simple reason, but I couldn't find it (in
> the Writing R Extensions or in any of the R help lists, including
> R-sig-mac).
>
> ANY hint greatly appreciated!
>
> Cheers,
>
> Carsten
>
>
> For what it's worth, here my system details:
>
> R version 2.12.0 (2010-10-15)
> Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
>
> locale:
> [1] de_DE.UTF-8/de_DE.UTF-8/C/C/de_DE.UTF-8/de_DE.UTF-8
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> The C++-functions starts like this:
> #include <R.h>
>
> #include <stdio.h>
> #include <iostream>
> #include <fstream>
> #include <string>
> #include "stdlib.h"
> #include "time.h"
>
> #include "myhelperfunctions.h"
>
> using namespace std;
>
> extern "C" {
>
> ... various long C++ functions without any change for inclusion into R
> (apart from renaming "main" to "myfun")
>
> }
>
>
>
>
>
> --
> Dr. Carsten F. Dormann
> Department of Computational Landscape Ecology
> Helmholtz Centre for Environmental Research-UFZ
> (Department Landschaftsökologie)
> (Helmholtz Zentrum für Umweltforschung - UFZ)
> Permoserstr. 15
> 04318 Leipzig
> Germany
>
> Tel: ++49(0)341 2351946
> Fax: ++49(0)341 2351939
> Email: carsten.dormann at ufz.de
> internet: http://www.ufz.de/index.php?de=4205
>
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