Unknown pragma when compiling OpenMP with g++

Question

I am working on C++ code which contains openmp pragmas. While trying to compile with g++, I am receiving the following error message:

ignoring #pragma omp parallel [-Werror=unknown-pragmas]

I understand that the error is from not using fopenmp flag with in the makefile. I have tried including the fopenmp flag to the CXXFLAGS. Still, it is not working.

Would anyone think of solutions to work around this issue?

Note: This question looks like a repeat question of similar question on same error and I have gone through and tried it too. Therefore, I would request this question not to be flagged as repeat question.

Answer 1

This is warning appears if you compile OpenMP code without the -fopenmp flag. The g++ man page tells us what -fopenmp does:

Enable handling of OpenMP directives "#pragma omp" in C/C++ and "!$omp" in Fortran. When -fopenmp is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v3.0 http://www.openmp.org/. This option implies -pthread, and thus is only supported on targets that have support for -pthread