[Mpi-forum] MPI_DATATYPE_NULL when count=0

Balaji, Pavan balaji at anl.gov
Tue Jan 12 21:43:55 CST 2016

It is valid.  The buffer and type are significant only when the count is non-zero.

 -- Pavan

Sent from my iPhone

On Jan 13, 2016, at 11:26 AM, Jeff Hammond <jeff.science at gmail.com<mailto:jeff.science at gmail.com>> wrote:

Is it allowed to communicate messages with (buffer=NULL,count=0,type=MPI_DATATYPE_NULL)?

George thinks MPI_DATATYPE_NULL cannot be used even when count=0, which I think is ridiculous, particularly when one makes the analogy to buffer=NULL.

See http://www.open-mpi.org/community/lists/users/2016/01/28255.php for the thread in question.

There is example code in MPI that uses this behavior.  George and I agree that example text is non-normative, but I cannot imagine how this example came to exist without the Forum believing it to be valid.


Jeff Hammond
jeff.science at gmail.com<mailto:jeff.science at gmail.com>
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