[OMPI users] help

[Lesiano 16 via users]

Hi,

for the following code:

#include <mpi.h>

int main() {
    MPI_Init(NULL, NULL);
    int world_rank, world_size;
    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
    MPI_Comm_size(MPI_COMM_WORLD, &world_size);

    MPI_Offset offset;
    MPI_Status status;
    MPI_File fh;

    MPI_File_open(MPI_COMM_WORLD, "myfile", MPI_MODE_CREATE |
MPI_MODE_WRONLY,
            MPI_INFO_NULL, &fh);

    offset = world_rank * sizeof(int);

    if (world_rank == 3) {
       MPI_File_write_at(fh, offset, &world_rank, 1, MPI_INT, &status);
    }

    MPI_File_close(&fh);

    MPI_Finalize();

    return 0;
}

I get the following output using hexdump -C myfile:

00000000  00 00 00 00 00 00 00 00  00 00 00 00 03 00 00 00
 |................|
00000010

My question is, can I assume that when skipping the beginning of the file
that MPI will fill up with zeros? Or is it implementation dependent?

I have read the standard, but I could not found anything
meaningful expected for:

"Initially, all processes view the file as a linear byte stream, and each
process views data in its own native representation (no data representation
conversion is performed). (POSIX files are linear byte streams in the
native representation.) The file view can be changed via the
MPI_FILE_SET_VIEW routine."

which I am not sure is actually relevant or not.

Thanks a lot