MPI_File_preallocate(3OpenMPI)											    MPI_File_preallocate(3OpenMPI)

NAME

       MPI_File_preallocate - Preallocates a specified amount of storage space	at the beginning of a file (collective).

SYNTAX

       C Syntax
	   #include <mpi.h>
	   int MPI_File_preallocate(MPI_File fh, MPI_Offset size)

       Fortran Syntax (see FORTRAN 77 NOTES)
	   INCLUDE 'mpif.h'
	   MPI_FILE_PREALLOCATE(FH, SIZE, IERROR)
		  INTEGER FH, IERROR
		  INTEGER(KIND=MPI_OFFSET_KIND) SIZE

C++ Syntax
       #include <mpi.h>
       void MPI::File::Preallocate(MPI::Offset size)

INPUT
/OUTPUT PARAMETER
       fh	 File handle (handle).

INPUT PARAMETER

       size	 Size to preallocate file, in bytes (integer).

OUTPUT PARAMETER

       IERROR	 Fortran only: Error status (integer).

DESCRIPTION

       MPI_File_preallocate  ensures that storage space is allocated for the first size bytes of the file associated with fh. MPI_File_preallocate
       can be a very time-consuming operation.

       MPI_File_preallocate is collective; all processes in the group must pass identical values for size. Regions of the file	that  have  previ-
       ously  been  written are unaffected. For newly allocated regions of the file, MPI_File_preallocate has the same effect as writing undefined
       data. If size is larger than the current file size, the file size increases to size. If size is less than or  equal  to	the  current  file
       size, the file size is unchanged.

       The  treatment  of  file  pointers,  pending  nonblocking  accesses,  and  file	consistency  is  the  same  as	with MPI_File_set_size. If
       MPI_MODE_SEQUENTIAL mode was specified when the file was opened, it is erroneous to call this routine.

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

	    INTEGER*MPI_OFFSET_KIND SIZE

       where MPI_OFFSET_KIND is a constant defined in mpif.h and gives the length of the declared integer in bytes.

NOTES

       When using the collective routine MPI_File_set_size on a UNIX file, if the size that is set is smaller than the current file size, the file
       is truncated at the position defined by size. If the size is set to be larger than the current file size, the file  size  becomes  the  set
       size.  When  the file size is increased this way with MPI_File_set_size, new regions are created in the file with displacements between the
       old file size and the larger, newly set file size.

       Sun MPI I/O does not necessarily allocate file space for such new regions. You may reserve file space either by using  MPI_File_preallocate
       or by performing a read or write to certain 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++ func-
       tions 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_preallocate(3OpenMPI)