MPI_File_read(3)

NAME
     MPI_File_read - Uses individual file pointer to read a file

SYNOPSIS
     C:

          #include "mpi.h"

          int MPI_File_read(MPI_File fh, void *buf, int count,
          MPI_Datatype datatype, MPI_Status status)


     Fortran:

          INCLUDE "mpif.h" (or USE MPI)

          <type> BUF(*)
          INTEGER fh, count, datatype, status(MPI_STATUS_SIZE),
          ierror

          CALL MPI_FILE_READ(fh, buf, count, datatype,
          status, ierror)


DESCRIPTION
     MPI_File_read reads a file using the individual file pointer.  This
     routine accepts the following arguments:

     fh        Specifies the file handle (handle)

     buf       Returns the initial address of the buffer (choice)

     count     Specifies the number of elements in the buffer (nonnegative
               integer)

     datatype  Specifies the data type of each buffer element (handle)

     status    Returns the status object (status)

     ierror    Specifies the return code value for successful completion,
               which is in MPI_SUCCESS.  MPI_SUCCESS is defined in the mpif.h
               file.

   Notes for Fortran
     All MPI objects (for example, MPI_Datatype, MPI_Comm, MPI_File) are of
     type INTEGER.

EXAMPLES
     The following Fortran code fragment is an example of reading a file until
     the end of file is reached:

     !   Read a preexisting input file until all data has been read.
     !   Call routine "process_input" if all requested data is read.
     !   The Fortran 90 "exit" statement exits the loop.

     integer   bufsize, numread, totprocessed, status(MPI_STATUS_SIZE)
           parameter (bufsize=100)
           real      localbuffer(bufsize)

     call MPI_FILE_OPEN( MPI_COMM_WORLD, 'myoldfile', &
                               MPI_MODE_RDONLY, MPI_INFO_NULL, myfh, ierr )
           call MPI_FILE_SET_VIEW( myfh, 0, MPI_REAL, MPI_REAL, 'native', &
                               MPI_INFO_NULL, ierr )
           totprocessed = 0
           do
              call MPI_FILE_READ( myfh, localbuffer, bufsize, MPI_REAL, &
                                  status, ierr )
              call MPI_GET_COUNT( status, MPI_REAL, numread, ierr )
              call process_input( localbuffer, numread )
              totprocessed = totprocessed + numread
              if ( numread < bufsize ) exit
           enddo

     write(6,1001) numread, bufsize, totprocessed
     1001  format( "No more data:  read", I3, "and expected", I3, &
                   "Processed total of", I6, "before terminating job." )

     call MPI_FILE_CLOSE( myfh, ierr )


SEE ALSO
     MPI_File_open(3), MPI_IO(3)