Rcpp C/C++ using structs and char*

Question

Newbie to C/C++ and Rcpp.

I'm currently trying to modify examples I find (in this case I modified the "yada" module example http://cran.r-project.org/web/packages/Rcpp/vignettes/Rcpp-modules.pdf) and extend them to test my understanding.

The example I have currently compiles but, does not have the expected behaviour. My guess it that I'm missing something, but I can't determine what is missing from I find in the docs. Any help would be much appreciated.

the example code is below.

library(inline)
fx=cxxfunction(,plugin="Rcpp",include='#include<Rcpp.h>
#include<string>

typedef struct containerForChars {const char *b;} containChar;

containChar cC;

const char* toConstChar(std::string s){return s.c_str();}

void setB(std::string s){
    cC.b = toConstChar(s);
}

std::string getB(void){
    std::string cs = cC.b;
    return cs;
}
RCPP_MODULE(ex1){
  using namespace Rcpp;
  function("setB",&getB);
  function("getB",&getB);
}')
mod=Module("ex1",getDynLib(fx))
f<-mod$setB
g<-mod$getB
f("asdf")
g()

Instead of f("asdf") setting cC.b to "asdf", I get the following error,

Error in f("asdf") : unused argument ("asdf")

My hope is that the arg to f() will be set as the value for cC.b, and g() will retrieve or get the value I set with f. My guess is that whatever magic that Module and RCPP_MODULE do isn't capable of using the struct I defined. I guess hoping for it to work wasn't enough :P.

Answer 1

Common typo. Instead of

 function("setB",&getB);
 function("getB",&getB);

do

 function("setB",&setB);     # set, not get
 function("getB",&getB);

and then everything works:

R> f("asdf")    
R> g()          
[1] "asdf" 
R>   

I'd also add library(inline) at the top.