How to link to already compiled external shared libraries in RCPP using Makevars?

Question

I have looked at multiple places but failed to find a simple example for my problem.

What I need is to be able to use multiple .so files which I have (together with .h files).

A simple example would be:

I have the following files: a.h, a.cpp the function jeden - this is my R library, accessor.cpp which exposes to R the function dwa from external library libdwa.so. I have the header file dwa.h and this library libdwa.so.

I can manage building binary package (and everything works fine) only and only then when I put the library file libdwa.so into the directory '/usr/lib' (I use Debian). But it is not partable solution.

Where I should put the library "dwa" files (dwa.h and libdwa.so) and what flags add in the Makevars file to get portable solution?

SUMMARY ADDED

I summarize my results here. I believe some extremaly simple examples are useful at start.

1. 2 external libraries put inside inst:

   /inst/include/dwa.h
   /inst/include/trzy.h
   /inst/jeden/libdwa.so
   /inst/jeden/libtrzy.so
   

2. configure file /configure has the form (test6 is a name of the package):

   #!/bin/bash
   rpath=$(${R_HOME}/bin/Rscript -e 'cat(file.path(.libPaths()[1], "test6", "jeden"))') #'
   sed -e"s|@rpath@|"${rpath}"|" src/Makevars.in > src/Makevars
   
   exit 0
   

3. The file /src/Makevars.in has the form:

   CXX_STD = CXX11
   
   PKG_CPPFLAGS = -I../inst/include/ -I.
   PKG_LIBS     = -ldwa -ltrzy -L../inst/jeden -Wl,-rpath,@rpath@
   

4. The /src/accessor.cpp expose the libraries function to R:

   #include <Rcpp.h>
   #include "../inst/include/dwa.h"
   #include "../inst/include/trzy.h"
   
   // [[Rcpp::export]]
   Rcpp::String r_dwa() {
     Rcpp::String res = dwa();.
     return res;
   }
   
   // [[Rcpp::export]]
   Rcpp::String r_trzy() {
     Rcpp::String res = trzy();.
     return res;
   }
   

5. Pure R library _/src/hello_world.cpp_ also exists:

   #include <Rcpp.h>
   using namespace Rcpp;
   
   // [[Rcpp::export]]
   String hello_world() {
     String hw = "Hello World";
     return hw ;
   }
   

6. Finaly /NAMESPACE file:

   useDynLib("test6", .registration=TRUE)
   
   import("Rcpp")
   importFrom("utils", "object.size", "packageVersion")
   exportPattern("^[[:alpha:]]+")
   

Building source and binary packages was successful but only source one is usefull as the binary has path to the libraries written rigidly.

Answer 1

Let's assume you have a directory structure like

/opt/dwa/include/dwa.h
/opt/dwa/lib/libdwa.so

In that case you could use is src/Makevars:

PKG_CPPFLAGS = -I/opt/dwa/include
PKG_LIBS = -L/opt/dwa/lib -ldwa -Wl,-rpath,/opt/dwa/lib

Of course, this is still not portable, since the path to the library and header files is hard coded. To circumvent this, one uses a template file, e.g. src/Makevars.in

PKG_CPPFLAGS = @DWA_INC@
PKG_LIBS = @DWA_LIB@

and writes a configure script that inspects the environment and creates src/Makevars based on the findings. There are different strategies for writing configure scripts. I typically use autoconf, e.g. in RcppArrayFire or dqmagic.