[R] interfacing C++ using .Call

[Prof Brian Ripley]

On Tue, 17 Feb 2004, Sundar Dorai-Raj wrote:

> Hi folks,
>    I apologise if this is in the documentation somewhere, but I can't 
> seem to find it. I also did a search of CRAN without any success. I'm 
> using R-1.8.1 (pre-compiled) on Windows 2000 with Rtools and mingw 2.0.0 
> (which includes gcc/g++ 3.2).
> 
> I'm trying to link some C++ code from another application to R using the 
> .Call interface and am experiencing some problems. I was able to compile 
> and link the example from Section 4.6 in R-exts.pdf without any 
> difficulty. But if I take a more complicated example that uses SEXP I'm 
> able to compile but not link. Here's an example:
> 
> Take the "lapply2" code on page 49 of R-exts.pdf and save to "test.c". 
> Be sure to add
> 
> #include <R.h>
> #include <Rdefines.h>

That should be <Rinternals.h>, as in R-exts.c in the sources.

> to the top of the file.
> 
> Now at the command line type:
> 
>  > Rcmd SHLIB test.c
> making test.d from test.c
> gcc   -Id:/R/rw1081/src/include -Wall -O2   -c test.c -o test.o
> ar cr test.a *.o
> ranlib test.a
> gcc  --shared -s  -o test.dll test.def test.a 
> -Ld:/R/rw1081/src/gnuwin32  -lg2c -lR
> 
> Works fine (though I haven't tested in R but at least the dll is 
> created). Now remove all files except "test.c" and rename to "test.cpp".
> 
>  > Rcmd SHLIB test.cpp
> making test.d from test.cpp
> g++   -Id:/R/rw1081/src/include -Wall -O2   -c test.cpp -o test.o
> ar cr test.a *.o
> ranlib test.a
> g++  --shared -s  -o test.dll test.def test.a 
> -Ld:/R/rw1081/src/gnuwin32  -lg2c -lR
> test.a(test.o.b)(.text+0x61):test.cpp: undefined reference to 
> `Rf_length(SEXPREC*)'
> test.a(test.o.b)(.text+0x6e):test.cpp: undefined reference to 
> `Rf_isNewList(SEXPREC*)'
> test.a(test.o.b)(.text+0x82):test.cpp: undefined reference to 
> `Rf_isFunction(SEXPREC*)'
> test.a(test.o.b)(.text+0x99):test.cpp: undefined reference to 
> `Rf_isEnvironment(SEXPREC*)'
> test.a(test.o.b)(.text+0xb7):test.cpp: undefined reference to 
> `Rf_lang2(SEXPREC*, SEXPREC*)'
> test.a(test.o.b)(.text+0xc2):test.cpp: undefined reference to 
> `Rf_protect(SEXPREC*)'
> test.a(test.o.b)(.text+0xcf):test.cpp: undefined reference to 
> `Rf_allocVector(unsigned, int)'
> test.a(test.o.b)(.text+0xda):test.cpp: undefined reference to 
> `Rf_protect(SEXPREC*)'
> test.a(test.o.b)(.text+0xf5):test.cpp: undefined reference to 
> `Rf_getAttrib(SEXPREC*, SEXPREC*)'
> test.a(test.o.b)(.text+0x107):test.cpp: undefined reference to 
> `Rf_setAttrib(SEXPREC*, SEXPREC*, SEXPREC*)'
> test.a(test.o.b)(.text+0x113):test.cpp: undefined reference to 
> `Rf_unprotect(int)'
> test.a(test.o.b)(.text+0x129):test.cpp: undefined reference to 
> `VECTOR_ELT(SEXPREC*, int)'
> test.a(test.o.b)(.text+0x132):test.cpp: undefined reference to 
> `SETCADR(SEXPREC*, SEXPREC*)'
> test.a(test.o.b)(.text+0x13e):test.cpp: undefined reference to 
> `Rf_eval(SEXPREC*, SEXPREC*)'
> test.a(test.o.b)(.text+0x14a):test.cpp: undefined reference to 
> `SET_VECTOR_ELT(SEXPREC*, int, SEXPREC*)'
> make: *** [test.dll] Error 1
> 
> Adding extern "C" {} does not help the problem. Can anybody replicate 
> this? Is there something I'm missing?

You need to do that.  If I wrap the whole file (including the #includes) 
in that, it works for me.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595