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Calling C++ from R

5 messages · Douglas Bates, Dirk Eddelbuettel, Xiaochun Sun

Original
Xiaochun Sun
# 
Hi All,

I am new to this area and use Rcpp to call C++ from R and try to build the
package under Windows 7. I use Rtools and R 2.10.1 32bit. Everything works
fine with me, except using R functions like "rnorm" or "runif" in the C++
code. When I use "R CMD check" the package, it always return error 

** libs
  making DLL ...
g++ -I"c:/PROGRA~2/R/R-210~1.1/include"  
-I"c:/PROGRA~2/R/R-210~1.1/library/Rcpp/include"     -O2 -Wall  -c func.cpp
-o func.o
func.cpp: In function 'SEXPREC* myfunction(SEXPREC*, SEXPREC*)':
func.cpp:220: error: 'rgamma' was not declared in this scope
func.cpp:225: error: 'rnorm' was not declared in this scope
func.cpp:244: error: 'runif' was not declared in this scope
func.cpp:274: error: 'rbeta' was not declared in this scope
make: *** [func.o] Error 1
  ... done

although I already put <Rmath.h>, <R.h> and <math.h> in the header file.
//////////////////////////////////////////////////
The func.cpp file has the following structure 

#include "func.h"
SEXP myfunction(SEXP a, SEXP b) {
}
//////////////////////////////////////////////
The  header file "func.h" has the following content

#include <cstdio>
#include <Rcpp.h>
#include <math.h>
#include <R.h>
#include <Rmath.h>
RcppExport SEXP myfunction(SEXP a, SEXP b);
/////////////////////////////////////////
What could the problem be?

Many thanks, 
Xiaochun
Douglas Bates
# 
It is more effective to send such inquiries to the Rcpp-devel mailing
list which I am cc'ing on this reply.
On Thu, Jan 20, 2011 at 3:05 PM, mtck1982 <xiaoch.sun at gmail.com> wrote:
It is not clear if you are trying to use the Rcpp "sugar"
constructions, which can apply to entire vectors, of if you are using
the functions in the R API.  If the latter then you will need to
preface the name with Rf_, as in Rf_runif. Those are the actual names
of the functions.  The Rinternals.h file defines a number of aliases,
such as runif, but in Rcpp those aliases are turned off, so as to
avoid name clashes.

You should note that when calling random number generator functions
the programmer is responsible for getting and restoring the seed
structure.  I can't remember the details right now and I am on a
Windows system without the sources so I will rely on someone else to
fill in the details.
Dirk Eddelbuettel
#
On 21 January 2011 at 06:44, Douglas Bates wrote:
| It is more effective to send such inquiries to the Rcpp-devel mailing
| list which I am cc'ing on this reply.

Correct.
| On Thu, Jan 20, 2011 at 3:05 PM, mtck1982 <xiaoch.sun at gmail.com> wrote:
| >
| > Hi All,
| >
| > I am new to this area and use Rcpp to call C++ from R and try to build the
| > package under Windows 7. I use Rtools and R 2.10.1 32bit. Everything works
| > fine with me, except using R functions like "rnorm" or "runif" in the C++
| > code. When I use "R CMD check" the package, it always return error
| >
| > ** libs
| > ?making DLL ...
| > g++ -I"c:/PROGRA~2/R/R-210~1.1/include"
| > -I"c:/PROGRA~2/R/R-210~1.1/library/Rcpp/include" ? ? -O2 -Wall ?-c func.cpp
| > -o func.o
| > func.cpp: In function 'SEXPREC* myfunction(SEXPREC*, SEXPREC*)':
| > func.cpp:220: error: 'rgamma' was not declared in this scope
| > func.cpp:225: error: 'rnorm' was not declared in this scope
| > func.cpp:244: error: 'runif' was not declared in this scope
| > func.cpp:274: error: 'rbeta' was not declared in this scope
| > make: *** [func.o] Error 1
| > ?... don
| 
| It is not clear if you are trying to use the Rcpp "sugar"
| constructions, which can apply to entire vectors, of if you are using
| the functions in the R API.  If the latter then you will need to
| preface the name with Rf_, as in Rf_runif. Those are the actual names
| of the functions.  The Rinternals.h file defines a number of aliases,
| such as runif, but in Rcpp those aliases are turned off, so as to
| avoid name clashes.
| 
| You should note that when calling random number generator functions
| the programmer is responsible for getting and restoring the seed
| structure.  I can't remember the details right now and I am on a
| Windows system without the sources so I will rely on someone else to
| fill in the details.

The easiest is to just declared a variable of type 

    Rcpp::RNGScope

which saves state when entering the local scope (ie "set of curly braces")
and restores it when leaving, thanks to what one can do with C++. Here is
an example Romain wrote to the rcpp-devel list in October:

   In addition, we have the RNGScope class, whose constructor calls=20
   GetRNGstate and destruvctor calls PutRNGstate, so that you can do :

   fx <- cxxfunction( , '
           RNGScope scope ;
           NumericVector x = rgamma( 10, 1, 1 ) ;
           return x ;
   ', plugin="Rcpp" )

   fx()

That's self-contained example for inline, using the rgamma sugar function.
You need the Rcpp:: prefix or a 'using namespace Rcpp;' when you use that in
your own source code.

Dirk
1 day later
Dirk Eddelbuettel
#
On 21 January 2011 at 11:32, Xiaochun Sun wrote:
| Many thanks for your reply. Rf_rnorm works very good with me.

Glad to hear it helped, and let us know if you have other questions.

Cheers, Dirk