Hello OMPI_Developers, When I compile my C++ code with Open MPI version 4.0.3 or 4.0.4 (I think that 4.0.2 and 4.0.1 would have the same problem), I get many of warnings like (1 per source file):
/work/software/x86_64/openmpi-4.0.4/include/mpi.h:316:16: warning: "__STDC_VERSION__" is not defined, evaluates to 0 [-Wundef] I use g++ 9.3.1 on Fedora 31 Linux with many warnings options enabled (like -Wundef to report the use of undefined macros) but I have the same problem on CentOS 7.6 with the system compiler. This problem is caused by the fact that, starting with Open MPI version 4.0.1, mpi.h try to use the _Static_assert() macro defined by the C11 language to cleanly state that a given symbol is no longer available because it was deprecated by the MPI 3.0 standard. To see if it is available, it checks the __STDC_VERSION__ macro as follow (mpi.h, line 316): # elif (__STDC_VERSION__ >= 201112L) This macro is not defined by the C++ standard (or at least g++ doesn't define it) so it would be cleaner if it would be tested only if __cplusplus is not defined. Also if __cplusplus is defined and >= 201103L (C++11), the static_assert() keyword could be used instead of _Static_assert(). Thanks a lot for looking at how to fix this little annoyance. Martin Audet
