Writing an R Package Calling C/C++ Functions

The following two references provide detailed instruction.  Among other resources that can easily be found by google, these two seem to be the most useful to me.

1. A note by Carlies Geyer. This explains how to call C/C++ (and Fortran) functions from R.
2. A tutorial by Alan Lenarcic. This explains how to write an R package (in particular for a Windows system).

However, in addition I struggled a little bit to figure out the following questions. I was working on a Windows system and these problems might well disappear on a different system. The discussion below is based on the knowledge of the two references mentioned above. Basically, to call C/C++ functions,

1. compile the C/C++ codes into a shared library (.dll in Windows and .so (.o) in linux), 
2. load the shared library by dyn.load("LIBNAME"), and 
3. call the compiled C function by .C("FUNNAME",...). Here LIBNAME is the name of the shared library file and FUNNAME is the name of the C function.

This part is clearly described in the two references mentioned above. 

1. How to obtain returned values from C functions?

The C functions should have no return value. To return some values from a C function to R, one should set an argument as the value passer. Recall that in the C functions to be called by R, all the arguments are pointers. Therefore, the C functions should assign the to-be-returned value(s) to the value(s) pointed by this value-passer pointer.

2. How to call C++ functions?

One can have C++ functions in the source code (e.g. dealing with sophisticated data structure that cannot be handled easily by C). However, the function to be called from R must be of C extern format. To call C++ functions from R, one should have

extern "C" {
    void demoFunction(double *arg1, double *arg2) //all the arguments must be pointers.
    {
    // within the function, one can call other C++ functions though.
    ......
    }
}

and then call demoFunction from R as usual by .C("demoFunction", as.double(arg1), as.double(arg2)).

3. How to build a package calling C/C++ functions?

Lenarcic's tutorial described clearly how to build an R package. But it seems to me that to build an R package calling C/C++ functions, one crucial step is missing in that tutorial (this might be due to the difference of the systems and versions of the R). One needs to add the following R function:

.First.lib <- function(lib, pkg)
{
    library.dynam("LIBNAME", pkg, lib)
}

in the R files to be compiled. Otherwise I encountered an error when calling dyn.load(). The function .First.lib() is called when the package is loaded.

Updated January 21, 2013: In the latest version (currently 2.15.2) of R, .First.lib no longer exists and is replaced by .onLoad. (It took me a whole afternoon to install the latest R, rebuild the entire package, and install the package successfully in my computer: R and Rtools both need to be updated, otherwise the same source code wouldn't pass R CMD check; somehow surprisingly, I need to manually create this folder in user/Documents/R/win-library/2.15 so that R CMD INSTALL can run successfully...)