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.