MPI_File_read_at(3)                Open MPI                MPI_File_read_at(3)



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.




1.4.1                            Jan 14, 2010              MPI_File_read_at(3)
