R help - Aug 2003 - how to call a C program from R function

Martin Olivier wrote:
> Hi all,
> 
> I would like to call a C program from R function. I tried to use the 
> .C() function
> without success. I need a very simple example (such as the hello 
> program) to understand
Do you want to call a C program (executable) or a shared library? If you 
want to run a compiled program simply use system() or shell()
> how it works. Could you give a  such example?
> (I use the  1.7.1 Version of R with linux)
> 
> Does it work in the case of a C++ program instead of a C programm?
If you want to call a shared library (or DLL), please look into the 
Manual "writing R extensions" and look for the "convolve
example".

For a very simple "hello-function" see the "C++" example
below. Please
check if you have installed the correct compiler on Linux and look into 
the manual how to compile a shared library. On Linux it is:

R CMD SHLIB test.cpp


Thomas P.

-----------------------------------------------------------
A simple example, but there are better in the docs ;-) e.g. building a 
package.



==========================================================// File test.cpp:

#include <R.h>
#include <Rinternals.h>

extern "C" {

void testarr(int* n, double* x) {
     for (int i = 0; i < *n; i++) {
        x[i] = 2 * i;
     }
   }
}
==========================================================## file test.R

dyn.load("test.so")

testarr <- function(x) {
   .C("testarr", as.integer(length(x)), x=as.double(x))$x
}

print(testarr(1:10))

dyn.unload("test.so")

On Thu, 28 Aug 2003, Martin Olivier wrote:
> Hi all,
> 
> I would like to call a C program from R function. I tried to use the 
> .C() function
> without success. I need a very simple example (such as the hello 
> program) to understand
> how it works. Could you give a  such example?
There is one in Writing R Extensions.  `Hello world' be too simple: you do 
need to know how to return results.
> (I use the  1.7.1 Version of R with linux)
> 
> Does it work in the case of a C++ program instead of a C programm?
See Writing R extensions for details and examples.

-- 
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

Hi all,

I would like to call a C program from R function. I tried to use the 
.C() function
without success. I need a very simple example (such as the hello 
program) to understand
how it works. Could you give a  such example?
(I use the  1.7.1 Version of R with linux)

Does it work in the case of a C++ program instead of a C programm?

Best regards,
Olivier

-- 

-------------------------------------------------------------
Martin Olivier
INRA - Unit? prot?omique           LIRMM - IFA/MAB
2, Place Viala                     161, rue Ada
F-34060 Montpellier C?dex 1        34392 Montpellier C?dex 5	

Tel : 04 99 61 26 02               Tel : O4 67 41 86 71
martinol at ensam.inra.fr