# MPI_File_set_view

## NAME

MPI_File_set_view − Changes process’s view of data in file (collective).

## SYNTAX

C Syntax
#include <mpi.h>
int MPI_File_set_view(MPI_File fh, MPI_Offset disp,

|  | MPI_Datatype etype, MPI_Datatype filetype,
|  | char *datarep, MPI_Info info)

## Fortran Syntax (see FORTRAN 77 NOTES)

INCLUDE ’mpif.h’
MPI_FILE_SET_VIEW(FH, DISP, ETYPE,

| FILETYPE, DATAREP, INFO, IERROR)
| INTEGER FH, ETYPE, FILETYPE, INFO, IERROR
| CHARACTER*(*) DATAREP
| INTEGER(KIND=MPI_OFFSET_KIND) DISP

## C++ Syntax

#include <mpi.h>
void MPI::File::Set_view(MPI::Offset disp,

| const MPI::Datatype& etype,
| const MPI::Datatype& filetype, const char* datarep,
| const MPI::Info& info)

## INPUT/OUTPUT PARAMETER

| fh |  | File handle (handle). |

## INPUT PARAMETERS

| disp |  | Displacement (integer). |
| etype |  | Elementary data type (handle). |
| filetype |  | File type (handle). See Restrictions, below. |
| datarep |  | Data representation (string). |
| info |  | Info object (handle). |

## OUTPUT PARAMETER

| IERROR |  | Fortran only: Error status (integer). |

## DESCRIPTION

The MPI_File_set_view routine changes the process’s view of the data in the file -- the beginning of the data accessible in the file through that view is set to disp; the type of data is set to etype; and the distribution of data to processes is set to filetype. In addition, MPI_File_set_view resets the independent file pointers and the shared file pointer to zero. MPI_File_set_view is collective across the fh; all processes in the group must pass identical values for datarep and provide an etype with an identical extent. The values for disp, filetype, and info may vary. It is erroneous to use the shared file pointer data-access routines unless identical values for disp and filetype are also given. The data types passed in etype and filetype must be committed.

The disp displacement argument specifies the position (absolute offset in bytes from the beginning of the file) where the view begins.

The MPI_File_set_view interface allows the user to pass a data-representation string to MPI I/O via the datarep argument. To obtain the default value (or "native"), pass NULL. The user can also pass information via the info argument. See the HINTS section for a list of hints that can be set. For more information, see the MPI-2 standard.

## HINTS

The following hints can be used as values for the info argument.

SETTABLE HINTS:

- MPI_INFO_NULL

- shared_file_timeout: Amount of time (in seconds) to wait for access to the shared file pointer before exiting with MPI_ERR_TIMEDOUT.

- rwlock_timeout: Amount of time (in seconds) to wait for obtaining a read or write lock on a contiguous chunk of a UNIX file before exiting with MPI_ERR_TIMEDOUT.

- noncoll_read_bufsize: Maximum size of the buffer used by MPI I/O to satisfy read requests in the noncollective data-access routines. (See NOTE, below.)

- noncoll_write_bufsize: Maximum size of the buffer used by MPI I/O to satisfy write requests in the noncollective data-access routines. (See NOTE, below.)

- coll_read_bufsize: Maximum size of the buffer used by MPI I/O to satisfy read requests in the collective data-access routines. (See NOTE, below.)

- coll_write_bufsize: Maximum size of the buffer used by MPI I/O to satisfy write requests in the collective data-access routines. (See NOTE, below.)

NOTE: A buffer size smaller than the distance (in bytes) in a UNIX file between the first byte and the last byte of the access request causes MPI I/O to iterate and perform multiple UNIX read() or write() calls. If the request includes multiple noncontiguous chunks of data, and the buffer size is greater than the size of those chunks, then the UNIX read() or write() (made at the MPI I/O level) will access data not requested by this process in order to reduce the total number of write() calls made. If this is not desirable behavior, you should reduce this buffer size to equal the size of the contiguous chunks within the aggregate request.

- mpiio_concurrency: (boolean) controls whether nonblocking I/O routines can bind an extra thread to an LWP.

- mpiio_coll_contiguous: (boolean) controls whether subsequent collective data accesses will request collectively contiguous regions of the file.

NON-SETTABLE HINTS:

- filename: Access this hint to get the name of the file.

## FORTRAN 77 NOTES

The MPI standard prescribes portable Fortran syntax for the DISP argument only for Fortran 90. FORTRAN 77 users may use the non-portable syntax

INTEGER*MPI_OFFSET_KIND DISP

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.

MPI API Index