Calling R Function from C++

Question

I would like to, within my own compiled C++ code, check to see if a library package is loaded in R (if not, load it), call a function from that library and get the results b

Answer 1

There is Rcpp which allows you to easily extend R with C++ code, and also have that C++ code call back to R. There are examples included in the package which show that.

But maybe what you really want is to keep your C++ program (i.e. you own main()) and call out to R? That can be done most easily with RInside which allows you to very easily embed R inside your C++ application---and the test for library, load if needed and function call are then extremely easy to do, and the (more than a dozen) included examples show you how to. And Rcpp still helps you to get results back and forth.

Edit: As Martin was kind enough to show things the official way I cannot help and contrast it with one of the examples shipping with RInside. It is something I once wrote quickly to help someone who had asked on r-help about how to load (a portfolio optimisation) library and use it. It meets your requirements: load a library, accesses some data in pass a weights vector down from C++ to R, deploy R and get the result back.

// -*- mode: C++; c-indent-level: 4; c-basic-offset: 4;  tab-width: 8; -*-
//
// Simple example for the repeated r-devel mails by Abhijit Bera
//
// Copyright (C) 2009         Dirk Eddelbuettel 
// Copyright (C) 2010 - 2011  Dirk Eddelbuettel and Romain Francois

#include                     // for the embedded R via RInside

int main(int argc, char *argv[]) {

    try {
        RInside R(argc, argv);          // create an embedded R instance 

        std::string txt = "suppressMessages(library(fPortfolio))";
        R.parseEvalQ(txt);              // load library, no return value

        txt = "M <- as.matrix(SWX.RET); print(head(M)); M";
        // assign mat. M to NumericMatrix
        Rcpp::NumericMatrix M = R.parseEval(txt); 

        std::cout << "M has " 
                  << M.nrow() << " rows and " 
                  << M.ncol() << " cols" << std::endl;

        txt = "colnames(M)";        // assign columns names of M to ans and
        // into string vector cnames
        Rcpp::CharacterVector cnames = R.parseEval(txt);   

        for (int i=0; i

This rinside_sample2.cpp, and there are lots more examples in the package. To build it, you just say 'make rinside_sample2' as the supplied Makefile is set up to find R, Rcpp and RInside.