From: snir@XXXXXXXXXX
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To: Nicholas Nevin - Sun HPC High Performance Computing <nevin@XXXXXXXXXXXXXXXXX>
cc: mpi-core@XXXXXXXXXXX
Date: Thu, 25 Mar 1999 18:22:37 -0500
Subject: Re: clarification on inter-language interoperability of attributes
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It's a bad idea to store and retrieve integer attributes in C -- since C stores
and retrieves attributes of type void* (pointers). You can either
1. Trust type coertion to work OK. I.e.
 int ub;
 void* tagub;

    MPI_Comm_put_attr(..., (void*)ub,...);
    MPI_Comm_get_attr(..., &tagub, ...);
    ub = (int)tagub;

this code, of course, is not portable.

2. Allocate memory for the integer attribute, and cache a pointer to the
allocated memory.
int ub;
int *tagub

tagub = (*int)malloc(sizeof ub);
*tagub = ub;
MPI_Comm_put_attr(..., tagub,...);
MPI_Comm_get_attr(..., &tagub,...);
ub = *tagub;





Marc Snir
Senior Manager, Scalable Parallel Systems
IBM T J Watson Research Center, PO Box 218, Yorktown Heights 10598
Tel: 914 945 3204 (862 3204) Fax: 914 945 4425 (862 44245)
URL: http://www.research.ibm.com/people/s/snir