[Rcpp-devel] Debugging Rcpp code

[Hadley Wickham]

Ooops, I completely misinterpreted the std::vector API.  To insert the
elements I need to do:

  for(x_it = x.begin(), i_it = i.begin(); x_it != x.end(); ++x_it, ++i_it) {
    int i = *i_it;
    if (i > groups.size()) {
      groups.resize(i);
    }
    groups[i - 1].push_back(*x_it);
  }

Hadley

On Fri, Nov 16, 2012 at 8:36 AM, Hadley Wickham <h.wickham at gmail.com> wrote:
> Hi all,
>
> I'm attempting to write a simple version of tapply in C++ (see
> attached).  However, when I run tapply2(1, 1, sum) (which should
> return 1), R segfaults.  If I run R with gdb, I get the following
> stack trace:
>
> #0  0x03942120 in tapply2 (x=@0xbfffda68, i=@0xbfffda58,
> fun=@0xbfffda50) at tapply.cpp:22
> #1  0x0394298a in Rcpp::CppFunction_WithFormals3<Rcpp::Vector<14>,
> Rcpp::Vector<14>, Rcpp::Vector<13>, Rcpp::Function>::operator()
> (this=0x7f71c0, args=0xbfffdabc) at Module_generated_CppFunction.h:311
> #2  0x0385b8b1 in InternalFunction_invoke ()
> ...
>
> where line 22 is return out;
>
> I suspect it's something to do with the my coercion between
> std::vector and NumericVector to call the function, or between the
> SEXP output and NumericVector to store the output:
>
>   std::vector< std::vector<double> >::iterator g_it = groups.begin();
>   NumericVector::iterator o_it = out.begin();
>   for(; g_it != groups.end(); ++g_it, ++o_it) {
>     *o_it = as<double>(fun(wrap(*g_it)));
>   }
>
> I'd appreciate any hints as to how to solve this particular problem,
> as well as any general debugging strategies.
>
> Thanks!
>
> Hadley
>
> --
> RStudio / Rice University
> http://had.co.nz/



-- 
RStudio / Rice University
http://had.co.nz/