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MPI_File_read_at(3OpenMPI)                                                        MPI_File_read_at(3OpenMPI)



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. FOR-TRAN FORTRAN
       TRAN 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.




Open MPI 1.2                                   September 2006                     MPI_File_read_at(3OpenMPI)