From romain at r-enthusiasts.com  Thu Feb 11 10:08:38 2010
From: romain at r-enthusiasts.com (Romain Francois)
Date: Thu, 11 Feb 2010 10:08:38 +0100
Subject: [Rd] LinkingTo and C++
Message-ID: <4B73C916.4090705@r-enthusiasts.com>

Hello,

I've been trying to make LinkingTo work when the package linked to has 
c++ code.

I've put dumb packages to illustrate this emails here ; 
http://addictedtor.free.fr/misc/linkingto

Package A defines this C++ class:

class A {
public:
	A() ;
	~A() ;
	SEXP hello() ;
} ;

Package B has this function :

SEXP say_hello(){
	A a ;
	return a.hello() ;
}

headers of package A are copied into inst/include so that package B can 
have.

LinkingTo: A

in its DESCRIPTION file.

Also, package B has the R function ;

g <- function(){
	.Call("say_hello", PACKAGE = "B")
}

With this I can compile A and B, but then I get :

$ Rscript -e "B::g()"
Error in dyn.load(file, DLLpath = DLLpath, ...) :
   unable to load shared library '/usr/local/lib/R/library/B/libs/B.so':
   /usr/local/lib/R/library/B/libs/B.so: undefined symbol: _ZN1AD1Ev
Calls: :: ... tryCatch -> tryCatchList -> tryCatchOne -> <Anonymous>

If I then add a Makevars in B with this :


# find the root directory where A is installed
ADIR=$(shell $(R_HOME)/bin/Rscript -e "cat(system.file(package='A'))" )

PKG_LIBS= $(ADIR)/libs/A$(DYLIB_EXT)


Then it works:

$ Rscript -e "B::g()"
[1] "hello"

So it appears that adding the -I flag, which is what LinkingTo does is 
not enough when the package "linking from" (B) actually has to link to 
the "linked to" package (A).

I've been looking at 
http://cran.r-project.org/doc/manuals/R-exts.html#Registering-native-routines 
but it seems only applicable to c(++) functions and not classes ...

What am I missing ? Should/can linkingto be extended in a way that 
accomodates c++

Romain


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Romain Francois
Professional R Enthusiast
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http://romainfrancois.blog.free.fr
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[Rd] LinkingTo and C++
Romain Francois