Unable to compile simple Rcpp function using c++11 - c++

Question

Problem background
After upgrading to macos-mojave I don't seem to be able to compile a simple Rcpp function that would use // [[Rcpp::plugins(cpp11)]]. I've tried:
Editing Makevars following this answer
Running xcode-select --install following linked discussion on compiling C under macos after upgrade.
Changing includes, string / string.h leads to the same error
Code
The function, I've drafted to generate the error:
#include <Rcpp.h>
#include <string.h> // std::string, std::stod
using namespace Rcpp;
// [[Rcpp::plugins(cpp11)]]
// [[Rcpp::export]]
NumericVector convertToDouble(Rcpp::StringVector x) {
// Numeirc vector to store results
NumericVector res;
// Double for converted values
double converted_double;
for(Rcpp::StringVector::iterator it = x.begin(); it != x.end(); ++it) {
// Get [] for vector element
int index = std::distance(x.begin(), it);
// Add results to vector
converted_double = std::stod(x[index]);
res.push_back(converted_double);
}
return res;
}
// Source / test
/*** R
Rcpp::sourceCpp(
file = "sample_stod.cpp",
embeddedR = FALSE,
verbose = TRUE,
rebuild = TRUE,
cleanupCacheDir = TRUE,
showOutput = TRUE)
convertToDouble(c("2.3", "34.25a", "abc32def.43", "12", "1.5"))
*/
Errors
>> Rcpp::sourceCpp(
+ file = "sample_stod.cpp",
+ embeddedR = FALSE,
+ verbose = TRUE,
+ rebuild = TRUE,
+ cleanupCacheDir = TRUE,
+ showOutput = TRUE)
Generated extern "C" functions
--------------------------------------------------------
#include <Rcpp.h>
// convertToDouble
NumericVector convertToDouble(Rcpp::StringVector x);
RcppExport SEXP sourceCpp_1_convertToDouble(SEXP xSEXP) {
BEGIN_RCPP
Rcpp::RObject rcpp_result_gen;
Rcpp::RNGScope rcpp_rngScope_gen;
Rcpp::traits::input_parameter< Rcpp::StringVector >::type x(xSEXP);
rcpp_result_gen = Rcpp::wrap(convertToDouble(x));
return rcpp_result_gen;
END_RCPP
}
Generated R functions
-------------------------------------------------------
`.sourceCpp_1_DLLInfo` <- dyn.load('/private/var/folders/7x/kwc1y_l96t55_rwlv35mg8xh0000gn/T/Rtmp2H7VYU/sourceCpp-x86_64-apple-darwin15.6.0-0.12.19/sourcecpp_295d2f3a47a3/sourceCpp_2.so')
convertToDouble <- Rcpp:::sourceCppFunction(function(x) {}, FALSE, `.sourceCpp_1_DLLInfo`, 'sourceCpp_1_convertToDouble')
rm(`.sourceCpp_1_DLLInfo`)
Building shared library
--------------------------------------------------------
DIR: /private/var/folders/7x/kwc1y_l96t55_rwlv35mg8xh0000gn/T/Rtmp2H7VYU/sourceCpp-x86_64-apple-darwin15.6.0-0.12.19/sourcecpp_295d2f3a47a3
/Library/Frameworks/R.framework/Resources/bin/R CMD SHLIB -o 'sourceCpp_2.so' --preclean 'sample_stod.cpp'
clang++ -std=gnu++11 -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -I"/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include" -I"/Users/huski/Documents/R Projects/RcppConversion" -I/usr/local/include -fPIC -Wall -g -O2 -c sample_stod.cpp -o sample_stod.o
sample_stod.cpp:17:28: error: no matching function for call to 'stod'
converted_double = std::stod(x[index]);
^~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/string:3910:30: note: candidate function not viable: no known conversion from 'Rcpp::Vector<16, PreserveStorage>::Proxy' (aka 'string_proxy<16, PreserveStorage>') to 'const std::__1::string' (aka 'const basic_string<char, char_traits<char>, allocator<char> >') for 1st argument
_LIBCPP_FUNC_VIS double stod (const string& __str, size_t* __idx = 0);
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/string:3930:30: note: candidate function not viable: no known conversion from 'Rcpp::Vector<16, PreserveStorage>::Proxy' (aka 'string_proxy<16, PreserveStorage>') to 'const std::__1::wstring' (aka 'const basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> >') for 1st argument
_LIBCPP_FUNC_VIS double stod (const wstring& __str, size_t* __idx = 0);
^
1 error generated.
make: *** [sample_stod.o] Error 1
Error in Rcpp::sourceCpp(file = "sample_stod.cpp", embeddedR = FALSE, :
Error 1 occurred building shared library.
>>
~/.R/Makevars
# Force use of compilers maintained by Homebrew
# Clang and clang++
CC=/usr/local/opt/llvm/bin/clang
CXX=/usr/local/opt/llvm/bin/clang++
CXX1X=clang-omp++
Tried passing CC \ CXX \ CXX1X variables to use compilers installed via Homebrew but does generate a different error message. All compilation attempts fail on
sample_stod.cpp:17:28: error: no matching function for call to 'stod'
Update: can't find stod
g++ --version
g++ --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-1000.11.45.2)
Target: x86_64-apple-darwin18.0.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
Current ~/.R/Makevars
# Force use of compilers maintained by Homebrew
# Clang and clang++
# CC=/usr/local/opt/llvm/bin/clang
# CXX=/usr/local/opt/llvm/bin/clang++
# CXX1X=clang-omp++
# Fortran
# FC=/usr/local/opt/gcc/bin/gfortran
# F77=/usr/local/opt/gcc/bin/gfortran
# CC=/usr/local/clang4/bin/clang
# CXX=/usr/local/clang4/bin/clang++
# LDFLAGS=-L/usr/local/clang4/lib
# CPPFLAGS="-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include"
CPPFLAGS="-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include"

Answer 1

So, outside of the initial issue with respect to the compiler shenanigans on macOS (covered here), you have to help out the compiler when converting to a std::string from a single value in Rcpp::StringVector in this case.
#include <Rcpp.h>
// [[Rcpp::plugins(cpp11)]]
// [[Rcpp::export]]
Rcpp::NumericVector convertToDouble(Rcpp::StringVector x) {
// Numeirc vector to store results
std::vector<double> res;
// Double for converted values
double converted_double;
for(Rcpp::StringVector::iterator it = x.begin(); it != x.end(); ++it) {
// Get [] for vector element
int index = std::distance(x.begin(), it);
// Help the conversion to string
std::string temp = Rcpp::as<std::string>(x[index]);
// Convert
converted_double = std::stod(temp);
// Add to a std vector... Do not use with Rcpp types
res.push_back(converted_double);
}
// Convert and return the Rcpp type as desired.
return Rcpp::wrap(res);
}
Then, we can run:
convertToDouble(c("2.3", "34.25a", "abc32def.43", "12", "1.5"))
# Error in convertToDouble(c("2.3", "34.25a", "abc32def.43", "12", "1.5")) : stod: no conversion
This errors at: abc32def.43
You may need to do additional cleaning of the string prior to trying a conversion...