[Rcpp-devel] [R] Help with integrating R and c/c++

Hi Christopher/ Dirk,

Thank you very much for your replys. I think the idea of using inline as you
suggest is the best way to start off with using c++ with R. I went through
your examples and also plenty I found on the net. I have been trying to run
some of these over the past few days, but have consistently been getting
this error message as soon as I run the 'cfunction' or 'cxxfunction'. For
example, in the syntax that Dirk sent,
R> library(inline) #Runs perfectly
?R> src <- 'std::cout << "Hello C++_From_R World" << std::endl;
return(Rcpp::wrap(42));' #Runs perfectly
?R> rohit <- cxxfunction(signature(), src, plugin="Rcpp")
Now, as soon as I run this line, R spills a whole lot of text out and gives
an error and a warning:
ERROR(s) during compilation: source code errors or compiler configuration
errors!
Program source:
?1:
?2: // includes from the plugin
?3:
?4: #include <Rcpp.h>
?5:
?6:
?7: #ifndef BEGIN_RCPP
?8: #define BEGIN_RCPP
?9: #endif
?10:
?11: #ifndef END_RCPP
?12: #define END_RCPP
?13: #endif
?14:
?15: using namespace Rcpp;
?16:
?17:
?18: // user includes
?19:
?20:
?21: // declarations
?22: extern "C" {
?23: SEXP file59046688( ) ;
?24: }
?25:
?26: // definition
?27:
?28: SEXP file59046688( ?){
?29: BEGIN_RCPP
?30: std::cout << "Hello C++_From_R World" << std::endl;
return(Rcpp::wrap(42));
?31: END_RCPP
?32: }
?33:
?34:
Error in compileCode(f, code, language = language, verbose = verbose) :
?Compilation ERROR, function(s)/method(s) not created!
In addition: Warning message:
running command 'C:\PROGRA~1\R\R-212~1.1/bin/i386/R CMD SHLIB
file59046688.cpp 2> file59046688.cpp.err.txt' had status 1

The "file59046688.cpp 2" ?changes every time I run a different function, but
the problem seems to be the same.

I installed and loaded the inline package (0.3.8) and then the Rcpp package
(0.9.0). I also tried reversing the order in which I load these, but still
no luck. I think if I can get just one of these programs to work, I will be
on my way. Can any of you tell me what I might be doing wrong?

For your question on what exacly I require, Christopher - I just need to use
a while loop. I have always been able to substitute for loops with some of
the apply functions in R, but can't seem to be able to replace the while
with a more efficient function. But the things that are required inside the
while loop, I have already implemented in R efficiently. So, I thought of
transfering just the while loop to a language that is faster with loops.

Thanks in advance.
On Mon, Feb 7, 2011 at 6:21 AM, Wray, Christopher <
christopher.wray.10 at ucl.ac.uk> wrote:

As Dirk says, using "inline" makes it real simple to start and to prototype
code.

You mention you have R functions you wish to "call" via Rcpp. Im not
certain I fully understand what you require here, but it is pretty simple to
pass R-side functions to C++ via Rcpp, and similarly its simple to send
compiled functions back to R-side as external pointers (and reuse them
elsewhere). Here is a toy example using a simple "user" function defined on
the R-side (user_F).

This is evaluated in R, passed as a "function" parameter to compiled C++
function and evaluated there, and then a compiled version of the function is
passed back to R as an external pointer, which you can send back to the C
side and evaluate:

<R> user_F=function(v){sum((1-v)*exp(-0.5*v))}

cpp <- '
NumericVector numvec(xvec);
NumericVector RetVec;
Function userR_f(fun);
List ATR;
typedef SEXP (*h_ptr)(SEXP);
RetVec = userR_f(numvec);
ATR["Fn_ptr"]=XPtr<h_ptr> (new h_ptr(&fme));
ATR["Fn_VAL"]=RetVec;
return ATR;
'
inc<-'
using namespace Rcpp;
SEXP fme(SEXP x){
NumericVector xx(x);
NumericVector yy=(1-xx)*exp(-0.5*xx);
double Ans=sum(yy);
return wrap(Ans);
}
'
<R> FN_CSide <- cxxfunction(signature(xvec = "numeric", fun = "function"
),cpp, , plugin = "Rcpp", includes = inc)

cppP <- '
typedef SEXP (*h_ptr)(SEXP);
XPtr<h_ptr>p(x);
NumericVector yy(y);
yy=(*p)(yy);
return yy;
'
<R> px<-cxxfunction(signature(x = "externalptr", y = "numeric" ),cppP, ,
plugin = "Rcpp", includes = "using namespace Rcpp; ")

<R> R_side=FN_CSide(seq(1,5),user_F)
<R> user_F(seq(1,5))
[1] -1.548486
<R> R_side
$Fn_ptr
<pointer: 0x0964c608>
$Fn_VAL
[1] -1.548486
<R> px(R_side$Fn_ptr,seq(1,5))
[1] -1.548486

I've broken it out to make the logic explicit. The above is sloppy - and
makes no attempt to treat memory de/allocation/gc/protection issues (which
you should consider) especially if you pass objects around, but it does try
to show you how the mechanics work.

Aside from looking up the Rcpp::sugar functionality used in places above,
you might also want to look at package "RcppArmadillo", if functions and
calculations involve linear algebra calcs/matrix operations. Hopefully this
gives you some food-for-thought to delve further into the
archives/documentation to find what you need.
chris

--
Thanks,
Rohit
Mob: 91 9819926213

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