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MPI_File_read_at - Reads a file at an explicitly specified offset
(blocking, noncollective).
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)
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
#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)
- fh
- File handle (handle).
- offset
- File offset (integer).
- count
- Number of elements in buffer (integer).
- datatype
- Data type of each buffer
element (handle).
- buf
- Initial address of buffer (choice).
- status
- Status object (status).
- IERROR
- Fortran only: Error status (integer).
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.
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.
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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