Date: Thu, 25 Mar 1999 16:37:05 -0500 (EST)
From: Nicholas Nevin - Sun HPC High Performance Computing <nevin@XXXXXXXXXXXXXXXXX>
To: mpi-core@XXXXXXXXXXX
Subject: clarification on inter-language interoperability of attributes
Sender: owner-mpi-core@XXXXXXXXXXX
Precedence: bulk
X-UIDL: d0b3972e30c60fcb55f6bde4e5f9c9d9


Hi, All. I need some clarification on the behaviour of MPI_Comm_get_attr
in the case of an architecture with 32 bit ints and 64 bit pointers.

Section 4.12.7 of the MPI-2 standard states that MPI will store
internally *address* sized attributes. It also states that an integer
valued attribute when accessed from C via MPI_Comm_get_attr will return
the address of a pointer to the integer valued attribute. 

This seems to imply that MPI_Comm_get_attr will return a pointer to
a 64 bit quantity. This however will break codes which do this.

    int *tagub;
    int ub;

    MPI_Comm_get_attr(MPI_COMM_WORLD, MPI_TAG_UB, &tagub, &flag);
    ub = *tagub;

Under this interpretation the code should be written something like this 

    MPI_Aint *tagub;
    MPI_Aint ub;

    MPI_Comm_get_attr(MPI_COMM_WORLD, MPI_TAG_UB, &tagub, &flag);
    ub = *tagub;

The same applies for MPI_Attr_get() since the bindings are defined to be
identical.

Is this what was intended?

Thanks, Nick.