On 23 July 2015 at 17:01, Jeffrey Walton wrote: > > g++ -DNDEBUG -g2 -O3 -Wall -fPIC -march=native -pipe -c rw.cpp > rw.cpp:130:0: warning: ignoring #pragma omp parallel [-Wunknown-pragmas] > #pragma omp parallel sections if(CRYPTOPP_RW_USE_OMP) > ^ Pretty ugly, but if you want the OpenMP directives to be dependent on whether OpenMP support is actually enabled you could do: #if _OPENMP #pragma omp section #endif (I haven't tested whether the omp pragma still works this way.)