This directory contains simple examples of using the .C and .Call
interfaces for calling compiled C code from R.  Usually you would use
the package mechanism to hide some of these details, but sometimes it
is useful to use this approach.


.C Interface
============

The file addoneDotC.c contains a function to add one to each element
of a vector.

Create a dynamically loadable library (DLL), also called a shared
object or a shared library, at the shell command line using

    R CMD SHLIB addoneDotC.c

This compiles the code and links it into a DLL.  On Linux this DLL is
called addoneDotC.so; other operating systems use other extensions

From within R evaluate the expression

    dyn.load("addoneDotC.so")

to load the shared library.  You will need to use the appropriate name
on other operating systems; one way to make the loadign expression
portable is to write

    dyn.load(paste("addoneDotC", .Platform$dynlib.ext, sep = ""))

Now load the R function addoneDotC defined in the file addoneDotC.R
with

    source("addoneDotC.R")

and try it out with something like

    addoneDotC(1:3)


.Call Interface
===============

The .Call interface is a little more involved but also more flexible.
The file addoneDotCall.c creates a .Call interface to the function
defined for the .C interface. Compile it to a shared library with

    R CMD SHLIB addoneDotCall.c

load the shared library into R with

    dyn.load("addoneDotCall.so")

and try it out with something like

    .Call("addoneDotCall", as.double(1:3))

It would be best to again wrap this in an R function.


Compiler Flags
==============

You can provide additional flags to the C compiler with the PKG_CFLAGS
environment variagle. For example, one way to ensure C code is
compiled with -Wall -pedantic is to use

    env PKG_CFLAGS="-Wall -pedantic" R CMD SHLIB addoneDotC.c

You can also set this variable in the file ~/.R/Makevars. This file
would contain the line

PKG_CFLAGS=-Wall -pedantic

You will need to create the directory ~/.R (i.e. the directory .R in
your home directory) if it does not exist.