[Rcpp-devel] Using Rcpp with C++11 and clang

[Dirk Eddelbuettel]

Hi Michael,

Congrats on your recent flooding of CRAN with packages :)

On 28 August 2012 at 18:46, Michael Braun wrote:
| Is it possible that there is some kind of incompatibility among clang, libc++ and Rcpp? Consider this super-simple example (filename is  tr1.cpp):
| 
| #include <Rcpp.h>
| RcppExport SEXP testtr1() {
|   return(Rcpp::wrap(0));
| }
| 
| If I compile it as a dynamic library with clang, I get:
| 
| clang -O3  -m64 -msse4.2 -std=c++11 -stdlib=libc++ -I/Library/Frameworks/R.framework/Headers -I/Library/Frameworks/R.framework/Resources/library/Rcpp/include   -c tr1.cpp -o tr1.o 
| 
| In file included from tr1.cpp:1:
| In file included from /Library/Frameworks/R.framework/Resources/library/Rcpp/include/Rcpp.h:27:
| /Library/Frameworks/R.framework/Resources/library/Rcpp/include/RcppCommon.h:143:10: fatal error: 'tr1/unordered_map' file not found
| #include <tr1/unordered_map>
|          ^
| 1 error generated.
| 
| This works fine with the Intel compiler, as well as with gcc version 4.6.1.
| 
| Looking at RcppCommon.h, I see that there are a number of checks, including the definition of HAS_TR!_UNORDERED_MAP.   Is it possible that this code defines this macro for clang, when it shouldn't?
| 
| The version of clang I am using is:
| 
| Apple clang version 4.0 (tags/Apple/clang-421.0.60) (based on LLVM 3.1svn)
| Target: x86_64-apple-darwin12.1.0
| Thread model: posix
| 
| Rcpp is version 0.9.13.  My OS is Mac OSX 10.8.1, and I have installed XCode 4.4.1, with the latest command line tools.
| 
| I see that this issue has been brought up in the past, but I have not been able to find a resolution.  Since clang appears to be Apple's preferred compiler in XCode, I thought you might like to know about this, and perhaps let me know if I have made some kind of mistake.

There are two (to three) distinct issues here:

i)  clang -- and I do from time to time test with clang which works just fine
    "as is", ie on my Linux box I simply say this in ~/.R/Makevars

    CXX=clang++
    CC=clang

    and R builds just fine, as does Rcpp.  As I follow whatever Ubuntu gives
    me, I am still at clang 3.0, but I expect no changes from clang 3.1

ii) c++11 -- and Romain and I were enthusiastic about it early as brings so
    many new features.  Only to be told by CRAN (and one vocal person in
    particular) that this is non-standard, non-portable, non-kosher, ...
    so we relented.  I still have this in ~/.R/Makevars

    #CXXFLAGS=            -g  -O3 -Wall -pipe -pedantic -Wno-variadic-macros 
    #CXXFLAGS=            -g0 -O3 -Wall -pipe -pedantic -Wno-variadic-macros 
    #CXXFLAGS= -std=c++0x -g  -O3 -Wall -pipe -pedantic -Wno-variadic-macros 

    so all it takes is to enable -std=c++0x.  AFAIK clang++ uses that switch too.

    But do understand that such code cannot go to CRAN until the
    powers-that-be decide otherwise.

Now, there could possibly be an intersection of issues with i) AND ii) but I
don't think so. Similarly, there could as always be something special going
on with OS X, in which case someone else will need to help you with the finer
aspects of that environment.

Hth,  Dirk


-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com