An implementation is allowed to implement MPI_WTIME, MPI_WTICK, PMPI_WTIME, PMPI_WTICK, and the handle-conversion functions ( MPI_Group_f2c, etc.) in Section Transfer of Handles , and no others, as macros in C.
 Advice to implementors.
Implementors should document which routines are implemented as macros.
( End of advice to implementors.)
 Advice to users.
If these routines are implemented as macros, they will not work with the MPI
( End of advice to users.)