A few weeks ago, I posted the Rffi package on the Omegahat repository.
It is an interface to libffi which is a portable mechanism for invoking native routines
without having to write and compile any wrapper routines in the native language.
In other words, we can use this in R to call C routines using only R code.
This enables us to call arbitrary routines and get back arbitrary values, including structures
arrays, unions, etc.

One could use the RGCCTranslationUnit package to obtain descriptions of routines and data
structures and then generate the interfaces to those routines via functions in Rffi.

Writing or generating C/C++ code for wrappers (see RGCCTranslationUnit) is still the way to
go in many ways, but Rffi is very convenient for dynamic invocations without any write and compile
setup costs.

As usual, you can install this from source from the Omegahat repository

install.packages(“Rffi”, repos = “http://www.omegahat.org/R”, type = “source”)

but you will need to have installed libffi.