[Rcpp-devel] About calling C/C++ functions in R

[Romain Francois]

Le 16/06/10 13:27, xiagao1982 a écrit :
> Thanks for your help! When will the new version 0.8.3 be released?

This is not planned yet. So you still have lots of time to read the 
documentation.

Romain

> ------------------------------------------------------------------------
> xiagao1982
> 2010-06-16
> ------------------------------------------------------------------------
> *发件人：* Romain Francois
> *发送时间：* 2010-06-16 17:15:35
> *收件人：* xiagao1982
> *抄送：* rcpp-devel
> *主题：* Re: [Rcpp-devel] About calling C/C++ functions in R
> Le 16/06/10 10:56, Romain Francois a écrit :
>  >
>  > Hi,
>  >
>  > I totally second Dirk in the advice about reading the appropriate
>  > documents. I would add the book from John Chambers "Programming with
>  > Data" as it has very clear chapters about R and C(++).
>  >
>  > Once you digested these documents, you can read the Rcpp-modules
>  > vignette from Rcpp, which might help you.
>  >
>  > Also, I just commited some code in Rcpp (which will be available in the
>  > next version of Rcpp : 0.8.3) that adds the Rcpp::InternalFunction
>  > class, that you can use like this:
>  >
>  > // grab the global environment
>  > Environment g = Environment::global_env() ;
>  >
>  > // assign the "hello" R variable to the internal function
>  > g["hello"] = InternalFunction( &hello ) ;
>  >
>  >
>  >
>  > Here is a complete example you can run from the R prompt:
>  >
>  > require( Rcpp)
>  > require( inline)
>  >
>  > inc <- '
>  >
>  > const char* hello( std::string who ){
>  > std::string result( "hello " ) ;
>  > result += who ;
>  > return result.c_str() ;
>  > }
>  >
>  > '
>  > code <- '
>  > Environment g = Environment::global_env() ;
>  > g["hello"] = InternalFunction( &hello ) ;
>  > return R_NilValue ;
>  > '
>  > fx <- cxxfunction( signature(), code, inc, plugin = "Rcpp" )
>  > f <- fx() # force loading the dynamic library
>  >
>  > hello( "world" )
>  >
>  > I have not tried it yet from RInside.
> Done. I added this as a new example "rinside_sample9.cpp".
> // -*- mode: C++; c-indent-level: 4; c-basic-offset: 4; tab-width: 8; -*-
> //
> // Simple example showing how expose a C++ function
> //
> // Copyright (C) 2010 Dirk Eddelbuettel and Romain Francois
> #include <RInside.h> // for the embedded R via RInside
> // a c++ function we wish to expose to R
> const char* hello( std::string who ){
> std::string result( "hello " ) ;
> result += who ;
> return result.c_str() ;
> }
> int main(int argc, char *argv[]) {
> // create an embedded R instance
> RInside R(argc, argv);
> // expose the "hello" function in the global environment
> R["hello"] = Rcpp::InternalFunction( &hello ) ;
> // call it and display the result
> std::string result = R.parseEval("hello('world')") ;
> std::cout << "hello( 'world') = " << result << std::endl ;
> exit(0);
> }
> Romain
>  > Romain
>  >
>  > Le 16/06/10 02:13, xiagao1982 a écrit :
>  >> Dear friends,
>  >> I am a newcomer of Rcpp and RInside. I installed them in my system and
>  >> successfully build the following example:
>  >> #include <RInside.h> // for the embedded R via RInside
>  >> Rcpp::NumericMatrix createMatrix(const int n) {
>  >> Rcpp::NumericMatrix M(n,n);
>  >> for (int i=0; i<n; i++) {
>  >> for (int j=0; j<n; j++) {
>  >> M(i,j) = i*10+j;
>  >> }
>  >> }
>  >> return(M);
>  >> }
>  > >
>  >> int main(int argc, char *argv[]) {
>  >> const int mdim = 4; // let the matrices be 4 by 4
>  >> SEXP ans;
>  >> RInside R(argc, argv); // create an embedded R instance
>  >> Rcpp::NumericMatrix M = createMatrix(mdim); // create and fill a sample
>  >> data Matrix
>  >> R["M"] = M; // assign C++ matrix M to R's 'M' var
>  >> std::string evalstr = "\
>  >> cat('Running ls()\n'); print(ls()); \
>  >> cat('Showing M\n'); print(M); \
>  >> cat('Showing colSums()\n'); Z <- colSums(M); print(Z); \
>  >> Z"; // returns Z
>  >> ans = R.parseEval(evalstr); // eval the init string -- Z is now in ans
>  >> Rcpp::NumericVector v(ans); // convert SEXP ans to a vector of doubles
>  >> for (int i=0; i< v.size(); i++) { // show the result
>  >> std::cout << "In C++ element " << i << " is " << v[i] << std::endl;
>  >> }
>  >> exit(0);
>  >> }
>  >> Now I add a function in the C++ code:
>  >> const char* hello( std::string who ){
>  >> std::string result( "hello " ) ;
>  >> result += who ;
>  >> return result.c_str() ;
>  >> }
>  >> And I try to call this function in R:
>  >> std::string txt = "ret = hello('Friends'); print(ret);";
>  >> R.parseEvalQ(txt); // eval string quietly, no result
>  >> It fails to do that.
>  >> Could you please tell me how to achieve that? Thanks very much!
>  >> Gao Xia
>  >> ------------------------------------------------------------------------
>  >> xiagao1982
>  >> 2010-06-16

-- 
Romain Francois
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http://romainfrancois.blog.free.fr
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