[Rcpp-devel] Expose cpp class with built-in boost odeint to R

[Simon Woodward]

Hi Ralf

Thank you so much, your advice was extremely helpful! It works now.
My simulation model will be 1000+ lines of C++, this is a prototype, I embedded the code inline to make it easier to post as a reprex to this forum.

Follow up questions:
- do I need to worry about destructing my global variable my_spring (the instance of my class)? If so, how do I do this? 
- for read/write efficiency, can/should I make a persistent link (Rccp::XPtr?) between the my_spring.variable property and an object or function in R? If so, how do I do this? Or is it better simply to copy-pass the data when needed and let Rccp handle the conversion from std::unordered_map<string,double> to an R named vector?

// https://www.r-bloggers.com/external-pointers-with-rcpp/

Thanks!

Simon 


-----Original Message-----
From: Rcpp-devel [mailto:rcpp-devel-bounces at lists.r-forge.r-project.org] On Behalf Of Ralf Stubner
Sent: Friday, 14 September 2018 8:05 PM
To: rcpp-devel at lists.r-forge.r-project.org
Subject: Re: [Rcpp-devel] Expose cpp class with built-in boost odeint to R

On 14.09.2018 05:17, Simon Woodward wrote:
> I am developing a simulation model in C++ and I want to expose it to R for testing. The model is in a C++ class and uses the boost::odeint library for numerical integration. I am also using an unordered_map to expose the model variables to the user.
> I am having some trouble exposing the class functionality to C++, either as separate // [[Rcpp::export]] methods or using RCPP_MODULE. The following code successfully instantiates the model and returns the unordered_map but crashes Rcpp if I try to access the advance(t,dt) method.

What do you mean with "crashes Rcpp"? On my system it mearly gives a compiler error:

/usr/include/c++/6/bits/stl_iterator_base_funcs.h: In instantiation of 'void std::advance(_InputIterator&, _Distance) [with _InputIterator = Rcpp::InputParameter<double>; _Distance = Rcpp::InputParameter<double>]':


> # sample code embedded in an R script

With the given ratio of C++ to R code it would have been better to use a
C++ file with R code embedded via /*** R ... */.

> library(Rcpp)
> 
> Sys.setenv("PKG_CXXFLAGS"='-I"C:/boost/boost_1_66_0"')

The BH package can help with that:

  // [[Rcpp::depends(BH)]]

> sourceCpp(code='
>           #include <unordered_map>
>           #include <string>
>           #define BOOST_CONFIG_SUPPRESS_OUTDATED_MESSAGE
>           #include <boost/numeric/odeint.hpp>
>           #include <Rcpp.h>
> 
>           // Enable C++11 via this plugin (Rcpp 0.10.3 or later)
>           // [[Rcpp::plugins(cpp11)]]
> 
>           using namespace std;

The above quoted error message indicates that your advance method and std::advance are getting mixed up. Remove this "using namespace std;"
and handle to resulting errors by using "std::" or "using std::...;".

BTW, for larger pieces of code I would also get rid of "using namespace Rcpp;".

cheerio
ralf

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