[Rcpp-devel] dyn.load error with particular functor

[nate russell]

Hello,

I am running into the "Error in dyn.load [...] unable to load shared object
['/tmp/...'] undefined symbol [_...]" error; however it is only happening
with one particular Rcpp function, which I find puzzling. Here is my .cpp
file containing two functions - I can compile the first one without any
issue (in its own file), but the second brings about the noted error
message:


#include <Rcpp.h>
#include <vector>
#include <string>
#include <algorithm>
// [[Rcpp::plugins(cpp11)]]

/*
 * Works fine.
 */

struct checkTwo {
  public:
    checkTwo(const std::string& s1_, const std::string& s2_)
    : s1(s1_), s2(s2_) {}
    int operator() (std::string x1, std::string x2) {
      return (s1==x1 && s2==x2 ? 1 : 0);
    }
  private:
    std::string s1;
    std::string s2;
};

// [[Rcpp::export]]
int count_if_if(const Rcpp::DataFrame& df,
                const std::string& c1,
                const std::string& c2)
{
  std::vector<std::string> vc1 = df["C1"];
  std::vector<std::string> vc2 = df["C2"];
  int N = df.nrows();

  std::vector<int> vcount;
  vcount.resize( N );


std::transform(vc1.begin(),vc1.end(),vc2.begin(),vcount.begin(),checkTwo(c1,c2));
  int total = std::accumulate(vcount.begin(),vcount.end(),0);

  return total;
}

/*
 * Does not compile.
 */

struct trackIdx {
  public:
    trackIdx(const std::string& s1_, const std::string& s2_)
    : s1(s1_),s2(s2_) {}
    int operator() (std::string x1, std::string x2) {
      tracker++;
      return ((s1==x1 && s2==x2) ? (tracker-1) : -1);
    }
  private:
    std::string s1;
    std::string s2;
    static int tracker;
};

// [[Rcpp::export]]
std::vector<int> mc_index(const Rcpp::DataFrame& df,
                          const std::string& c1,
                          const std::string& c2)
{
  std::vector<std::string> vc1 = df["C1"];
  std::vector<std::string> vc2 = df["C2"];
  int N = df.nrows();

  std::vector<int> vcount;
  vcount.resize( N );

  std::vector<int> result;
  result.resize( N );


std::transform(vc1.begin(),vc1.end(),vc2.begin(),vcount.begin(),trackIdx(c1,c2));
  std::copy_if(vcount.begin(),vcount.end(),result.begin(),
    [](int i) -> bool {
      return !(i<0);
    });

  return result;
}


The above functions (only "count_if_if" at the moment) can be tested like
this:

Df <- data.frame(
  C1=rep(LETTERS[1:4],each=15),
  C2=as.character(rep(rep(1:3,each=5),4)),
  C3=rep(rep(1:3,each=5),4),
  stringsAsFactors=FALSE)
##
count_if_if(Df,"B","3")
##
# mc_index(Df,"B","3")



The exact error message I am getting is:

Error in
dyn.load("/tmp/Rtmpw7VSkV/sourcecpp_27046ca49cd4/sourceCpp_67600.so") :
  unable to load shared object
'/tmp/Rtmpw7VSkV/sourcecpp_27046ca49cd4/sourceCpp_67600.so':
  /tmp/Rtmpw7VSkV/sourcecpp_27046ca49cd4/sourceCpp_67600.so: undefined
symbol: _ZN8trackIdx7trackerE


and judging by the last bit, "undefined symbol: _ZN8trackIdx7trackerE", it
looks like my "trackIdx" function object is the source of the problem.

I have tested this on two different platforms -

my network server running CentOS 7:

R version 3.1.1
Platform: x86_64-redhat-linux-gnu (64-bit)
Rcpp_0.11.3


and my laptop running Ubuntu 14.04:

R version 3.0.2
Platform: x86_64-pc-linux-gnu (64-bit)
Rcpp_0.11.2


Both of these machines use a reasonably up-to-date version of g++ that
supports c++11 (although I don't think this has anything to do with the
issue). I have never had any problems compiling Rcpp functions on either of
these platforms, yet the second function object & Rcpp function above
produce the same error on each machine. If anyone can explain what is going
wrong and/or suggest how to correct the problem with the above code I would
appreciate it very much.

Thank you,
Nathan Russell
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