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Subject: [OMPI users] printf and scanf problem of C code compiled with Open MPI
From: Meilin Bai (meilin.bai_at_[hidden])
Date: 2011-03-29 13:29:03


Dear open-mpi users:

I come across a little problem when running a MPI C program compiled with
Open MPI 1.4.3. A part of codes as follows:

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &myid);
    MPI_Get_processor_name(processor_name, &namelen);
    if (myid == 0) {
         printf("Please give N= ");
         //fflush(stdout);
         scanf("%d", &n);
         startwtime = MPI_Wtime();
     }

If comment out the sentence of "fflush(stdout);", it doesn't print out the
message till I input an integer n. And if I add the fflush function between
them, it works as expected, though comsumming time obviously.

However, when I compiled it with Mpich2-1.3.2p1, without fflush function in
the code, it works correctly.

Can anyone know what the matter is.

Thanks!

-- 
Meilin Bai