SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_File_preallocate(MPI_File fh, MPI_Offset size)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_FILE_PREALLOCATE(FH, SIZE, IERROR)
               INTEGER FH, IERROR
               INTEGER(KIND=MPI_OFFSET_KIND)   SIZE

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_File_preallocate(fh, size, ierror)
               TYPE(MPI_File), INTENT(IN) :: fh
               INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: size
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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 previously 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.

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 return result of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Sep 06, 2025                           MPI_FILE_PREALLOCATE(3)