R help - Oct 2002 - dyn.load and c-function

I've got a c function in a dll and have been able to call it from R. The
function is :

void __stdcall testfunc2(
  unsigned long *a,
  double        *b,
  unsigned long *c,
  double        *result )
{
    *result = 0;

    *result = (*a) * (*b) * (*c);
}

and the R code to call the function is as follows:

dyn.load("c:/openfvs/biometrics/debug/biometrics.dll" )
tf2 <- function( a, b, c, d )
  .C("testfunc2",
     as.integer(a),
     as.double(b),
     as.integer(c),
     as.double(d) )

I'm having a little trouble getting the value out of the R function. I would
like to be able to call the R funcion as :

val <- tf2( a, b, c )

when I'e tried to call the function as:

tf2 <- function( a, b, c )
  .C("testfunc2",
     as.integer(a),
     as.double(b),
     as.integer(c),
     as.double(d) )[[4]]

I get an "Object d not found" error...

how would I write the R part so that I can call my function the way I want
to?

Thanks,
jeff.





Jeff D. Hamann
Hamann, Donald & Associates, Inc.
PO Box 1421
Corvallis, Oregon USA 97339-1421
Bus. 541-753-7333
Cell. 541-740-5988
jeff_hamann at hamanndonald.com
www.hamanndonald.com


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"Jeff D. Hamann" <jeff_hamann at hamanndonald.com> writes:
> tf2 <- function( a, b, c )
>   .C("testfunc2",
>      as.integer(a),
>      as.double(b),
>      as.integer(c),
>      as.double(d) )[[4]]
> 
> I get an "Object d not found" error...
> 
> how would I write the R part so that I can call my function the way I want
> to?
Your C function assumes that d (or "result" as you call it on the
other side) exists with the relevant length. So you need to create it:

tf2 <- function( a, b, c ){
    d <- double(length(a))
   .C("testfunc2",
      as.integer(a),
      as.double(b),
      as.integer(c),
      d)[[4]]
}

or just 

tf2 <- function( a, b, c )
   .C("testfunc2",
      as.integer(a),
      as.double(b),
      as.integer(c),
      double(length(a)))[[4]]


-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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