io35cc.cc

The example for Boor USING MPI2

// example of parallel MPI read from single file, in C++
#include <iostream.h>
#include "mpi.h"

int main(int argc, char *argv[])
{
    int bufsize, *buf, count;
    char filename[128];
    MPI::Status status;

    MPI::Init();
    int myrank = MPI::COMM_WORLD.Get_rank();
    int numprocs = MPI::COMM_WORLD.Get_size();
    MPI::File thefile = MPI::File::Open(MPI::COMM_WORLD, "testfile",
                                        MPI::MODE_RDONLY,
                                        MPI::INFO_NULL);
    MPI::Offset filesize = thefile.Get_size();  // in bytes
    filesize    = filesize / sizeof(int);    // in number of ints
    bufsize     = filesize / numprocs + 1;   // local number to read
    buf = (int *) malloc (bufsize * sizeof(int));
    thefile.Set_view(myrank * bufsize * sizeof(int),
		     MPI_INT, MPI_INT, "native", MPI::INFO_NULL);
    thefile.Read(buf, bufsize, MPI_INT, &status);
    count = status.Get_count(MPI_INT);
    cout << "process " << myrank << " read " << count << " ints"
	 << endl;
    thefile.Close();
    MPI::Finalize();
    return 0;
}