invalid conversion from 'SEXP' to long int in Rcpp - rcpp

Question

I'm trying to run my cpp program with matrix from dlib in R. For hours I have been trying to run code, but I couldn't resolve one error. Can you help me?
There is fragment of my code:
#include <Rcpp.h>
#include <cmath>
#include <vector>
// [[Rcpp::depends(RcppEigen)]]
#include <RcppEigen.h>
// [[Rcpp::plugins(cpp11)]]
// [[Rcpp::depends(dlib)]]
#include <dlib/optimization/optimization.h>
using namespace Eigen;
using namespace std;
using namespace dlib;
typedef matrix<double,0,1> column_vector;
Unfortunately I can't compile code because of Source Cpp error:
~/R/win-library/3.4/Rcpp/include/Rcpp/internal/Exporter.h
Line 31 invalid conversion from 'SEXP' to long int [-fpermissive]
and logs from console:
C:/RBuildTools/3.4/mingw_64/bin/g++ -std=gnu++11 -I"C:/PROGRA~1/R/R-34~1.1/include" -DNDEBUG -I"C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include" -I"C:/Users/user_name/Documents/R/win-library/3.4/RcppEigen/include" -I"C:/Users/user_name/Documents/R/win-library/3.4/dlib/include" -I"C:/Users/user_name/Documents/project_name/cpp_to_R" -I"d:/Compiler/gcc-4.9.3/local330/include" -std=c++0x -O2 -Wall -mtune=core2 -c project_name.cpp -o project_name.o
In file included from C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/Rcpp/as.h:25:0,
from C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/RcppCommon.h:160,
from C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/Rcpp.h:27,
from project_name.cpp:1:
C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/Rcpp/internal/Exporter.h: In instantiation of 'Rcpp::traits::Exporter<T>::Exporter(SEXP) [with T = dlib::matrix<double, 0l, 1l>; SEXP = SEXPREC*]':
C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/Rcpp/as.h:87:51: required from 'T Rcpp::internal::as(SEXP, Rcpp::traits::r_type_generic_tag) [with T = dlib::matrix<double, 0l, 1l>; SEXP = SEXPREC*]'
C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/Rcpp/as.h:152:82: required from 'T Rcpp::as(SEXP) [with T = dlib::matrix<double, 0l, 1l>; SEXP = SEXPREC*]'
C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/Rcpp/InputParameter.h:72:62: required from 'Rcpp::ConstReferenceInputParameter<T>::ConstReferenceInputParameter(SEXP) [with T = dlib::matrix<double, 0l, 1l>; SEXP = SEXPREC*]'
project_name.cpp:279:80: required from here
C:/Users/user_name/Documents/R/win-library/3.4/Rcpp/include/Rcpp/internal/Exporter.h:31:31: error: invalid conversion from 'SEXP' to 'long int' [-fpermissive]
Exporter( SEXP x ) : t(x){}
^
In file included from C:/Users/user_name/Documents/R/win-library/3.4/dlib/include/dlib/optimization/../matrix.h:6:0,
from C:/Users/user_name/Documents/R/win-library/3.4/dlib/include/dlib/optimization/optimization_search_strategies.h:8,
from C:/Users/user_name/Documents/R/win-library/3.4/dlib/include/dlib/optimization/optimization.h:9,
from project_name.cpp:8:
C:/Users/user_name/Documents/R/win-library/3.4/dlib/include/dlib/optimization/../matrix/matrix.h:1019:18: note: initializing argument 1 of 'dlib::matrix<T, num_rows, num_cols, mem_manager, layout>::matrix(long int) [with T = double; long int num_rows = 0l; long int num_cols = 1l; mem_manager = dlib::memory_manager_stateless_kernel_1<char>; layout = dlib::row_major_layout]'
explicit matrix (
^
make: *** [project_name.o] Error 1
Warning message:
running command 'make -f "C:/PROGRA~1/R/R-34~1.1/etc/x64/Makeconf" -f "C:/PROGRA~1/R/R-34~1.1/share/make/winshlib.mk" CXX='$(CXX11) $(CXX11STD)' CXXFLAGS='$(CXX11FLAGS)' CXXPICFLAGS='$(CXX11PICFLAGS)' SHLIB_LDFLAGS='$(SHLIB_CXX11LDFLAGS)' SHLIB_LD='$(SHLIB_CXX11LD)' SHLIB="sourceCpp_78.dll" WIN=64 TCLBIN=64 OBJECTS="project_name.o"' had status 2
Error in Rcpp::sourceCpp("cpp_to_R/project_name.cpp") :
Error 1 occurred building shared library.
What's wrong here? I don't get it :(
Edit:
This error appears only when I add // [[Rcpp::export]] before function which uses my column_vector

Answer 1

The edit helps. My earlier comment was off. So basically, you typedef this
typedef matrix<double,0,1> column_vector;
and then use a column_vector and expect Rcpp to magically convert its content.
In short, it doesn't work that way. If you have new types that Rcpp does not yet know about then the burden is on you to provide new converters.
We wrote a vignette 'Extending Rcpp' about this which may help.