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NAME

       MPI_File_read_at  -  Reads  a  file  at  an explicitly specified offset
       (blocking, noncollective).

SYNTAX

       C Syntax
           #include <mpi.h>
           int MPI_File_read_at(MPI_File fh, MPI_Offset offset,
            void *buf, int count, MPI_Datatype datatype,
            MPI_Status *status)

Fortran Syntax (see FORTRAN 77 NOTES)

           INCLUDE 'mpif.h'
           MPI_FILE_READ_AT(FH, OFFSET, BUF, COUNT,
                   DATATYPE, STATUS, IERROR)
             <type>   BUF(*)
             INTEGER FH, COUNT, DATATYPE, STATUS(MPI_STATUS_SIZE), IERROR
             INTEGER(KIND=MPI_OFFSET_KIND) OFFSET

C++ Syntax

       #include <mpi.h>
       void MPI::File::Read_at(MPI::Offset offset, void* buf,
            int count, const MPI::Datatype& datatype,
            MPI::Status& status)

       void MPI::File::Read_at(MPI::Offset offset, void* buf,
            int count, const MPI::Datatype& datatype)

INPUT PARAMETERS

       fh        File handle (handle).

       offset    File offset (integer).

       count     Number of elements in buffer (integer).

       datatype  Data type of each buffer element (handle).

OUTPUT PARAMETERS

       buf       Initial address of buffer (choice).

       status    Status object (status).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       MPI_File_read_at attempts to read from the file associated with fh  (at
       the offset position) a total number of count data items having datatype
       type into the user's buffer buf.  The offset is in etype units relative
       to  the  current  view. That is, holes are not counted when locating an
       offset. The data is taken out of those parts of the file  specified  by
       the  current  view.  MPI_File_read_at  stores  the  number  of datatype
       elements actually read in status.   All  other  fields  of  status  are
       undefined. It is erroneous to call this function if MPI_MODE_SEQUENTIAL
       mode was specified when the file was opened.

FORTRAN 77 NOTES

       The MPI standard prescribes portable  Fortran  syntax  for  the  OFFSET
       argument only for Fortran 90. FORTRAN 77 users may use the non-portable
       syntax

            INTEGER*MPI_OFFSET_KIND OFFSET

       where MPI_OFFSET_KIND is a constant defined in  mpif.h  and  gives  the
       length of the declared integer in bytes.

ERRORS

       Almost  all MPI routines return an error value; C routines as the value
       of the  function  and  Fortran  routines  in  the  last  argument.  C++
       functions  do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before  the  error  value is returned, the current MPI error handler is
       called. For MPI I/O function errors, the default error handler  is  set
       to   MPI_ERRORS_RETURN.   The   error   handler  may  be  changed  with
       MPI_File_set_errhandler;     the     predefined      error      handler
       MPI_ERRORS_ARE_FATAL  may  be  used to make I/O errors fatal. Note that
       MPI does not guarantee that an MPI program can continue past an error.



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