On Feb 4 2011, Jeff Squyres wrote:

Question about MPI_UNDEFINED (and all the constants in the top table in MPI-2.2 p515): its type in C is listed as (const int) or unnamed (enum). But in Open MPI, we have this value in mpi.h as:

#define MPI_UNDEFINED -32766

So does MPICH2.

A #define of an integer constant will work just fine with other const int's, but it technically isn't a const int or unnamed enum.

Er, technically there isn't any such animal as a const int type! const is a type qualifier, that has effect only on lvalues (and which is ignored on rvalues).

Are we wrong? Or should I propose a ticket to change the wording of this table from:

C type: const int (or unnamed enum)

to

C type: const int, unnamed enum, or integer constant

That isn't any better - an integer constant isn't a type, and you need to be specific about what you mean by one of those if you are nitpicking, anyway - C has several different integer constant concepts. In any case, it isn't a problem. The first paragraph of A.1.1 states that a const int may be a literal integer constant. While the wording isn't ideal, there are a LOT of places where the MPI specification uses dubious (but not misleading) Fortran and C terminology. Regards, Nick Maclaren.