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)

       USE MPI
       ! or the older form: 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.