[Rcpp-devel] Package using Rcpp+openmp - fatal error: 'omp.h' file not found

On 10/08/2021, at 10:04 AM, Naeem Khoshnevis <khoshnevis.naeem at gmail.com> wrote:

Dear All, 

I hope this email finds you well and this is a right place to ask this question.

I recently submitted a package to CRAN (thanks for all supports); however, it has been archived. According to the email, the installation was not successful on some configurations. One of them is macOS (the other one is Solaris). 
I am using Rcpp and OpenMP; here are the initial lines of the code:
--------------
#include <Rcpp.h>
#include <omp.h>
using namespace Rcpp;

// [[Rcpp::plugins(openmp)]]

// [[Rcpp::export]]
IntegerVector compute_closest_wgps_helper(NumericVector a,
                                          NumericVector b,
                                          NumericVector cd,
                                          double sc) { 

------------------
Please see the following link for the entire code:
https://github.com/fasrc/CausalGPS/blob/master/src/compute_closest_wgps_helper.cpp

The error that I receive on R-hub is:

-------------------
compute_closest_wgps_helper.cpp:2:10: fatal error: 'omp.h' file not found
#include <omp.h>
         ^~~~~~~
1 error generated.
make: *** [compute_closest_wgps_helper.o] Error 1
ERROR: compilation failed for package ‘CausalGPS’
-------------------

Do you know a workaround for this issue? 
I understand some R developers do not use macOS; however, I have to address this comment.

Best regards, 
Naeem Khoshnevis

(I replied earlier but that seems to have gotten lost. Apologies to anybody
who may receive two copies, and thanks to Simon for his answer.  -- Dirk)


On 9 August 2021 at 17:04, Naeem Khoshnevis wrote:
| Do you know a workaround for this issue?

Wrap the #include by #ifdef _OPENMP and #endif

Test for presence of OpenMP (for example via a configure script).

Use the standard R compilation flags. RcppArmadillo uses

  PKG_CXXFLAGS = -I../inst/include @OPENMP_FLAG@
  PKG_LIBS= @OPENMP_FLAG@ $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)

where @OPENMP_FLAG@ gets set if OpenMP is found.  Other packages just use

  PKG_CXXFLAGS = $(SHLIB_OPENMP_CXXFLAGS)
  PKG_LIBS = $(SHLIB_OPENMP_CXXFLAGS) $(LAPACK_LIBS) $(BLAS_LIBS) $(FLIBS)

relying on R which sets SHLIB_OPENMP_CXXFLAGS.

Dirk

--
https://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org