using SHLIB to compile and load standalone Rcpp function - r

Question

I am trying to compile the following function with SHLIB (saved as foo.cpp):
#include <Rcpp.h>
RcppExport SEXP foo( SEXP x, SEXP y){
Rcpp::NumericVector xx(x), yy(y) ;
int n = xx.size() ;
Rcpp::NumericVector res( n ) ;
double x_ = 0.0, y_ = 0.0 ;
for( int i=0; i<n; i++){
x_ = xx[i] ;
y_ = yy[i] ;
if( x_ < y_ ){
res[i] = x_ * x_ ;
} else {
res[i] = -( y_ * y_) ;
}
}
return res ;
}
I try
$ R CMD SHLIB foo.cpp
/opt/local/bin/g++-mp-4.4 -I/opt/local/lib/R/include -I/opt/local/lib/R/include/x86_64 -I/opt/local/include -fPIC -pipe -O2 -m64 -c foo.cpp -o foo.o
foo.cpp:1:18: error: Rcpp.h: No such file or directory
foo.cpp:3: error: 'RcppExport' does not name a type
make: *** [foo.o] Error 1
How do I include this file, and is this the right way to compile a standalone function with Rcpp? Of course, I have installed Rcpp with install.packages('Rcpp').
Update:
Trying to find the location of Rcpp.h in R I get:
> system.file("lib", "Rcpp.h", package="Rcpp")
[1] ""
>
However,
> Rcpp:::LdFlags()
/opt/local/lib/R/library/Rcpp/lib/x86_64/libRcpp.a>
Update 2:
Looking at http://www.mail-archive.com/r-help#r-project.org/msg79185.html, I tried
$ PKG_CPPFLAGS=`Rscript -e 'Rcpp:::CxxFlags()'` \
> PKG_LIBS=`Rscript -e 'Rcpp:::LdFlags()'` \
> R CMD SHLIB foo.cpp
/opt/local/bin/g++-mp-4.4 -I/opt/local/lib/R/include -I/opt/local/lib/R/include/x86_64 -I/opt/local/lib/R/library/Rcpp/include -I/opt/local/include -fPIC -pipe -O2 -m64 -c foo.cpp -o foo.o
/opt/local/bin/g++-mp-4.4 -dynamiclib -Wl,-headerpad_max_install_names -undefined dynamic_lookup -single_module -multiply_defined suppress -L/opt/local/lib -o foo.so foo.o /opt/local/lib/R/library/Rcpp/lib/x86_64/libRcpp.a -L/opt/local/lib/R/lib/x86_64 -lR
and it generated foo.o and foo.so. How do I import this in R now?
Update 3:
So it can be loaded from dyn.load as
> dyn.load("foo.so")
> is.loaded("foo")
[1] TRUE
It can be called successfully as as
> .Call("foo",x=as.numeric(c(1,2,3)),y=as.numeric(c(4,5,6)))
[1] 1 4 9
Although the function is not visible as such.
> foo
Error: object 'foo' not found

Answer 1

Your question is clearly addressed in Question 2.4. of the Rcpp-FAQ.

Answer 2

The answer I found is that SHLIB needs to be provided the location of the Rcpp files. This can be done as
$ PKG_CPPFLAGS=`Rscript -e 'Rcpp:::CxxFlags()'` \
> PKG_LIBS=`Rscript -e 'Rcpp:::LdFlags()'` \
> R CMD SHLIB foo.cpp
Then, the compiled file can be loaded in R as
> dyn.load("foo.so")
and it can be called in R as
> .Call("foo",c(1,2,3),c(4,5,6))