From: snir@XXXXXXXXXX
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To: Nicholas Nevin - Sun HPC High Performance Computing <nevin@XXXXXXXXXXXXXXXXX>
cc: gropp@XXXXXXXXXXX,mpi-core@XXXXXXXXXXX
Date: Fri, 26 Mar 1999 16:20:21 -0500
Subject: Re: clarification on inter-language interoperability of attributes
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MPI_xxx_get_attr returns a void* value in "attr". If the attribute you accessed
is a Fortran attribute then (int*)attr will point to an INTEGER.
MPI_ADDRESS_KIND is irrelevant.

>

Unfortunately I left out some parentheses in my paraphrase of the
standard, it actually reads "When an integer valued attribute is
accessed from C or C++, then MPI_xxx_get_attr will return the
address of (a pointer to) the integer valued attribute."  This is
what I had meant to say.

So my question still stands.  Assuming Fortran INTEGER is 32 bits
and MPI_ADDRESS_KIND is 8, do I get back from MPI_xxx_get_attr a
pointer to a 32 bit integer or a 64 bit integer?

I see three cases and the answer may not be the same for all of
them.

1. predefined attributes. The answer may vary according to the
   attribute (window size is of type MPI_ADDRESS_KIND in Fortran).
2. attributes set in Fortran with MPI_ATTR_PUT
3. attributes set in Fortran with MPI_COMM_SET_ATTR

Of course it would be nice if the answer was the same for all the above cases
which would require that a pointer to a 64 bit integer be returned
in order to avoid possible data truncation.

-nick.