[Mpi-forum] MPI_UNDEFINED

[N.M. Maclaren]

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.