Rcpp Version 0.12.12
RcppInline/external_pointer.r

A simple example (using inline) of external Pointer use via Rcpp::XPtr

#!/usr/bin/env r
#
# Copyright (C) 2009 - 2010 Romain Francois
#
# This file is part of Rcpp.
#
# Rcpp is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# Rcpp is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Rcpp. If not, see <http://www.gnu.org/licenses/>.
require(Rcpp)
require(inline)
## NOTE: This is the old way to compile Rcpp code inline.
## The code here has left as a historical artifact and tribute to the old way.
## Please use the code under the "new" inline compilation section.
funx_old <- cxxfunction(signature(), '
/* creating a pointer to a vector<int> */
std::vector<int>* v = new std::vector<int> ;
v->push_back( 1 ) ;
v->push_back( 2 ) ;
/* wrap the pointer as an external pointer */
/* this automatically protected the external pointer from R garbage
collection until p goes out of scope. */
Rcpp::XPtr< std::vector<int> > p(v) ;
/* return it back to R, since p goes out of scope after the return
the external pointer is no more protected by p, but it gets
protected by being on the R side */
return( p ) ;
', plugin = "Rcpp" )
xp <- funx_old()
stopifnot( identical( typeof( xp ), "externalptr" ) )
# passing the pointer back to C++
funx_old <- cxxfunction(signature(x = "externalptr" ), '
/* wrapping x as smart external pointer */
/* The SEXP based constructor does not protect the SEXP from
garbage collection automatically, it is already protected
because it comes from the R side, however if you want to keep
the Rcpp::XPtr object on the C(++) side
and return something else to R, you need to protect the external
pointer, by using the protect member function */
Rcpp::XPtr< std::vector<int> > p(x) ;
/* just return the front of the vector as a SEXP */
return( Rcpp::wrap( p->front() ) ) ;
', plugin = "Rcpp" )
front <- funx_old(xp)
stopifnot( identical( front, 1L ) )
## NOTE: Within this section, the new way to compile Rcpp code inline has been
## written. Please use the code next as a template for your own project.
## Use of the cppFunction() gives the ability to immediately compile embedded
## C++ directly within R without having to worry about header specification or
## Rcpp attributes.
cppFunction('
Rcpp::XPtr< std::vector<int> > funx(){
/* creating a pointer to a vector<int> */
std::vector<int>* v = new std::vector<int> ;
v->push_back( 1 ) ;
v->push_back( 2 ) ;
/* wrap the pointer as an external pointer */
/* this automatically protected the external pointer from R garbage
* collection until p goes out of scope.
*/
Rcpp::XPtr< std::vector<int> > p(v) ;
/* return it back to R, since p goes out of scope after the return
* the external pointer is no more protected by p, but it gets
* protected by being on the R side
*/
return( p ) ;
}')
xp <- funx()
stopifnot( identical( typeof( xp ), "externalptr" ) )
# passing the pointer back to C++
cppFunction('
SEXP funx_pt(Rcpp::XPtr< std::vector<int> > p){
/* Wrapping x as smart external pointer */
/* The SEXP based constructor does not protect the SEXP from
* garbage collection automatically, it is already protected
* because it comes from the R side, however if you want to keep
* the Rcpp::XPtr object on the C(++) side
* and return something else to R, you need to protect the external
* pointer, by using the protect member function
*/
/* Just return the front of the vector as a SEXP */
return Rcpp::wrap(p->front());
}')
front <- funx_pt(xp)
stopifnot( identical( front, 1L ) )