[Rcpp-devel] Problems wrapping stl::vector<int>

[Romain Francois]

Hello, 

wrap is for converting an object of arbitrary class to an R object. It deduces what to do based on the class of what you pass it. So you usually don’t specify the template parameter. So you’d usually just write : 

return wrap(a); 

If you wanted to be explicit, then you would use: 

return wrap< std::vector<int> >( a ) ;

wrap returns a « SEXP » (any R object) which can be used by an IntegerVector constructor. So you can do: 

IntegerVector x( wrap(a) ) ;

or even:
 
IntegerVector  = as<IntegerVector>( wrap(a) ) ;

Romain

Le 3 janv. 2014 à 17:18, Alessandro Mammana <mammana at molgen.mpg.de> a écrit :

> Dear all,
> thank you again for this fantastic library.
> Sorry for the very stupid question, I looked before posting, but I
> couldn't find anything.
> I am encountering a problem when I try to do something very basic: I
> am trying to wrap a std::vector<int> to an IntegerVector:
> 
> In the file scratchpad.cpp:
> 
> // [[Rcpp::export]]
> IntegerVector test(){
>    std::vector<int> a;
>    a.push_back(1);a.push_back(2);a.push_back(3);
>    return wrap<IntegerVector>(a);
> }
> 
> when doing:
>> sourceCpp("scratchpad.cpp")
> 
> I get the error:
> 
> scratchpad.cpp: In function 'Rcpp::IntegerVector test()':
> scratchpad.cpp:181:30: error: no matching function for call to
> 'wrap(std::vector<int>&)'
> scratchpad.cpp:181:30: note: candidates are:
> In file included from
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/RcppCommon.h:120:0,
>                 from
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/Rcpp.h:27,
>                 from scratchpad.cpp:2:
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/Rcpp/internal/wrap.h:924:13:
> note: template<class T> SEXPREC* Rcpp::wrap(const T&)
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/Rcpp/internal/wrap.h:924:13:
> note:   template argument deduction/substitution failed:
> scratchpad.cpp:181:30: note:   cannot convert 'a' (type
> 'std::vector<int>') to type 'const Rcpp::Vector<13>&'
> In file included from
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/RcppCommon.h:120:0,
>                 from
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/Rcpp.h:27,
>                 from scratchpad.cpp:2:
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/Rcpp/internal/wrap.h:965:13:
> note: template<class InputIterator> SEXPREC* Rcpp::wrap(InputIterator,
> InputIterator)
> /package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include/Rcpp/internal/wrap.h:965:13:
> note:   template argument deduction/substitution failed:
> scratchpad.cpp:181:30: note:   cannot convert 'a' (type
> 'std::vector<int>') to type 'Rcpp::Vector<13>'
> scratchpad.cpp:183:1: warning: control reaches end of non-void
> function [-Wreturn-type]
> make: *** [scratchpad.o] Error 1
> g++ -I/package/mariux64/R/R-3.0.2/lib/R/include -DNDEBUG
> -I/usr/local/include
> -I"/package/mariux64/R/R-3.0.2/lib/R/library/Rcpp/include"    -fpic
> -g -O3 -Wall -pedantic -c scratchpad.cpp -o scratchpad.o
> Error in sourceCpp("scratchpad.cpp") :
> Error 1 occurred building shared library.
> 
> I must definitely be doing something very stupid. But what?
> 
> thanks in advance!
> Ale
> 
> -- 
> Alessandro Mammana, PhD Student
> Max Planck Institute for Molecular Genetics
> Ihnestraße 63-73
> D-14195 Berlin, Germany
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