[Rcpp-devel] c++ class as argument in rcpp function (using modules)

[Yasir Suhail]

Hi,

Other than the approaches mentioned, I can also specialize an
as<World>(SEXP) as

     template <>
     World as<World>(SEXP x) {
Rcpp::XPtr<World> ptr(x);
return World(ptr->greet());
     }

However, this also gives segfault at runtime when addMsg is called. The
final code, with alternative implementations commented out for
experimentation is:

#include <RcppCommon.h>
#include <string>
class World {
public:
    World() : msg("hello"){}
    World(const std::string s) : msg(s){}
    void set(std::string msg) { this->msg = msg; }
    std::string greet() const { return msg; }
    void addMsg(const World w2) {
this->msg = this->msg + w2.greet();
    }
//    World(SEXP x);
/*    World(SEXPREC* &w2) {
msg = ((World*)w2)->greet();
    }
*/
private:
    std::string msg;
};
namespace Rcpp{

template <> SEXP wrap(const World& object);
template <> World as<World>(SEXP x);
}
#include <Rcpp.h>


namespace Rcpp {
     template <>
     SEXP wrap( const World& object ){
         Language call( "new", Symbol( "World" ), object.greet() ) ;
         return call.eval() ;
     }
     template <>
     World as<World>(SEXP x) {
Rcpp::XPtr<World> ptr(x);
return World(ptr->greet());
     }
}


/*World::World(SEXP x) {
Rcpp::XPtr<World> ptr(x);
msg = ptr->greet();
}*/

//...

RCPP_MODULE(yada){
using namespace Rcpp ;
class_<World>( "World" )
    // expose the default constructor
    .constructor()
            .constructor<std::string>()
    .method( "greet", &World::greet , "get the message" )
.method( "set", &World::set     , "set the message" )
.method( "addMsg", &World::addMsg  , "add the message from another object"
);
}

Then, running with R -d gdb
> a <- new(World,"hello ")
> b <- new(World,"worlds")
> a$greet( )
[1] "hello "
> a$addMsg( b)

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000011000078
0x00000001042032df in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::basic_string ()
(gdb) bt
#0  0x00000001042032df in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::basic_string ()
#1  0x0000000104358b18 in Rcpp::as<World> ()
#2  0x000000010435d564 in Rcpp::CppMethod1<World, void, World>::operator()
()
#3  0x000000010435eadb in Rcpp::class_<World>::invoke_void ()
#4  0x0000000104164670 in CppMethod__invoke_void ()
#5  0x00000001000928e9 in do_External ()
#6  0x00000001000c4af7 in Rf_eval ()
#7  0x00000001000c6d99 in do_begin ()
#8  0x00000001000c48af in Rf_eval ()
#9  0x00000001000c7cf3 in Rf_applyClosure ()
#10 0x00000001000c4778 in Rf_eval ()
#11 0x00000001000fed75 in Rf_ReplIteration ()
#12 0x00000001000ff021 in R_ReplConsole ()
#13 0x00000001000ff590 in run_Rmainloop ()
#14 0x0000000100000e8b in main ()
(gdb)

Thanks!

On Wed, Dec 21, 2011 at 7:41 PM, Darren Cook <darren at dcook.org> wrote:

> Hello Yasir,
> Could you post your complete (minimal) code to the list. Then someone
> might be curious enough to try reproducing the problem.
>
> Darren
>
>
> On 2011-12-22 08:29, Yasir Suhail wrote:
> > Thanks Darren, Douglas, Richard, and Dirk!
> >
> > I can compile with the following definitions:
> >
> > World(SEXP x) {
> > Rcpp::XPtr<World> ptr(x);
> > msg = ptr->msg;
> > }
>
> > ...
>
>
> --
> Darren Cook, Software Researcher/Developer
>
> http://dcook.org/work/ (About me and my work)
> http://dcook.org/blogs.html (My blogs and articles)
>
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