Getting started with .C
Jeff Brown wrote:
Hi, I'm trying to learn to use .C, which lets one invoke compiled C code from within R. To do that, one has to first get the C code into R as a shared object, which (I think) means first compiling it (with COMPILE or SHLIB) and then loading it (with dyn.load()).
I would suggest taking it a step further and building an R package to hold your compiled code. The pros are: * It keeps the R wrapper scripts and other things you will end up creating packaged together with your code. * It handles compilation automagically during installation. * It handles loading the dylib for you. The only con I can think of is: * It takes ~2 extra minutes of your time to set up. But compared to other languages I have used this is a ridiculously small price to pay for the portability and organization offered by packages. I wrote a post that goes through step-by-step how to do this for the .Call() interface, including example code. You can find it at: http://n4.nabble.com/Writing-own-simulation-function-in-C-td1580190.html#a1580423 In "Writing R Extensions", p. 79, they give the following example of a C program for convolution of two vectors. (The details aren't important; it's just a function that does something to some stuff.) void convolve (double *a, int *na, double *b, int *nb, double *ab) { int i, j, nab = *na + *nb - 1; for(i = 0; i < nab; i++) ab[i] = 0.0; for(i = 0; i < *na; i++) for(j = 0; j < *nb; j++) ab[i + j] += a[i] * b[j] }
Jeff Brown wrote:
The document suggests calling it from R like this (again the details
aren't important):
conv <- function(a, b)
.C("convolve",
as.double(a),
as.integer(length(a)),
as.double(b),
as.integer(length(b)),
ab = double(length(a) + length(b) - 1))$ab
I wrote a file, "convolve.c", with nothing but the above C code in it. I
can't figure out how to compile it. I don't understand the syntax (no
parentheses?) and I always get the same information-free error message:
list.files()
[1] "AER" "convolve.c" "sendmailR"
R CMD SHLIB "compile.c"
Error: syntax error
COMPILE "compile.c"
Error: syntax error
R CMD SHLIB "compile"
Error: syntax error
COMPILE "compile"
Error: syntax error
R CMD SHLIB compile.c
Error: syntax error
COMPILE compile.c
Error: syntax error
R CMD SHLIB compile
Error: syntax error
COMPILE compile
Error: syntax error I'm using an Intel MacBook Pro running Leopard. At a console, typing "gcc --version" yields 4.2.1. I know I'm supposed to be using version 4.2; I thought 4.2.1 would qualify, but please let me know if I'm wrong about that. For guidance I've been relying on "Writing R Extensions", "R Installatino and Administration", the "R for Mac OS X Developer's Page", and the built-in help. Please let me know if there are other important resources I've missed. Many thanks, Jeff
All R CMD commands must be executed at the command line- i.e. in a Windows CMD shell or Unix/Linux bash shell. They are not meant for use inside the R interpreter. Hope this helps! -Charlie ----- Charlie Sharpsteen Undergraduate-- Environmental Resources Engineering Humboldt State University
View this message in context: http://n4.nabble.com/Getting-started-with-C-tp1837912p1837936.html Sent from the R devel mailing list archive at Nabble.com.