Romain,
I think your'e confusing two entirely different concepts here:
1) LinkingTo: allows a package to provide C-level functions to other packages
(see R-ext 5.4). Let's say package A provides a function foo by calling
R_RegisterCCallable for that function. If a package B wants to use that
function, it uses LinkingTo: and calls R_GetCCallable to obtain the function
pointer. It does not actually link to package A because that is in general not
possible - it simply obtains the pointers through R. In addition, LinkingTo:
makes sure that you have access to the header files of package A which help you
to cast the functions and define any data structures you may need. Since C++ is
a superset of C you can use this facility with C++ as long as you don't depend
on anything outside of the header files.
2) linking directly to another package's shared object is in general not
possible, because packages are not guaranteed to be dynamic libraries. They are
usually shared objects which may or may not be compatible with a dynamic
library on a given platform. Therefore the R-ext describes other way in which
you may provide some library independently of the package shared object to
other packages (see R-ext 5.8). The issue is that you have to create a separate
library (PKG/libs[/arch]/PKG.so won't work in general!) and provide this to
other packages. As 5.8 says, this is in general not trivial because it is very
platform dependent and the most portable way is to offer a static library.
To come back to your example, LinkingTo: A and B will work if you remove
Makevars from B (you don't want to link) and put your hello method into the A.h
header:
> library (B)
Loading required package: A
> .Call("say_hello", PACKAGE = "B")
[1] "hello"
However, your'e not really using the LinkingTo: facilities for the functions so
it's essentially just helping you to find the header file.
Cheers,
Simon
On Feb 11, 2010, at 4:08 AM, Romain Francois wrote:
> 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
>
>
> --
> Romain Francois
> Professional R Enthusiast
> +33(0) 6 28 91 30 30
> http://romainfrancois.blog.free.fr
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>
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>
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