On Fri, Aug 12, 2011 at 1:06 AM, Lars Wißler <jah...@googlemail.com> wrote:
> Dear R users,
>
> I want to call C code via the .C or .Call interface. This works fine
> with integer values but using doubles the array received in C will be
> set to zeros.
>
> I have tried the convolve examples (Writing R extensions, chapter 5.2)
> and still the resulting array consists of zeros.
>
> My code (shortened for my purposes. Original did not work either):
> ------------------------------------------------------------
> convolve.r
>
> a=array(1, c(4))
> b=array(3, c(4))
>
> print(a)
> print(b)
>
> .C("convolve",
> as.double(a),
> as.double(b))
>
> ----------------------------------------------------------------
> convolve.c
>
> void convolve(double* a, double* b){
> int i;
>
> for(i=0;i<4;i++) Rprintf("a: %d", a[i]);
> for(i=0;i<4;i++) Rprintf("b: %d", b[i]);
> }
The C code here is wrong for two reasons. Firstly, there's no
declaration for Rprintf(), because you don't include the header file.
Secondly, you're using %d to print, which means you are telling the
compiler you're passing ints to Rprintf(), but you are actually
passing doubles.
When I fix these problems the code works for me.
-thomas
Thomas Lumley
Professor of Biostatistics
University of Auckland
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