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Subject: [OMPI users] MPI_AllGather null terminator character
From: Gabriele Fatigati (g.fatigati_at_[hidden])
Date: 2012-01-13 02:32:41

Dear OpenMPI,

using MPI_Allgather with MPI_CHAR type, I have a doubt about
null-terminated character. Imaging I want to spawn node names where my
program is running on:


char hostname[MAX_LEN];


MPI_Allgather(hostname, MAX_STRING_LEN, MPI_CHAR, hostname_recv_buf,


Now, is the null-terminated character of each local string included? Or I
have to send and receive in MPI_Allgather MAX_STRING_LEN+1 elements?

Using Valgrind, in a subsequent simple strcmp:

for( i= 0; i< num_procs; i++){
                       ... doing something....

raise a warning:

Conditional jump or move depends on uninitialised value(s)
==19931== at 0x4A06E5C: strcmp (mc_replace_strmem.c:412)

The same warning is not present if I use MAX_STRING_LEN+1 in MPI_Allgather.

Thanks in forward.

Ing. Gabriele Fatigati
HPC specialist
SuperComputing Applications and Innovation Department
Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy                    Tel:   +39 051 6171722
g.fatigati [AT]