MPI_FILE_SET_SIZE(3)				     Open MPI				      MPI_FILE_SET_SIZE(3)

MPI_File_set_size — Resizes a file (collective).

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_File_set_size(MPI_File fh, MPI_Offset size)

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

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

INPUT PARAMETERS
       • fh: File handle (handle).

       • size: Size to truncate or expand file (integer).

OUTPUT PARAMETER
       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       MPI_File_set_size  resizes the file associated with the file handle fh, truncating UNIX files as necessary.
       MPI_File_set_size is collective; all processes in the group must pass identical values for size.

       When using MPI_File_set_size on a UNIX file, if size is larger than the current file size,  the	file  size
       becomes	size. If size is smaller than the current file size, the file is truncated at the position defined
       by size (from the beginning of the file and measured in	bytes).	 Regions  of  the  file	 which	have  been
       previously written are unaffected.

       MPI_File_set_size does not affect the individual file pointers or the shared file pointer.

       Note   that   the   actual   amount  of	storage	 space	cannot	be  allocated  by  MPI_File_set_size.  Use
       MPI_File_preallocate <#mpi-file-preallocate> to accomplish this.

       It is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened.

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>/MPI_Init_thread  <#mpi-init-thread>,
       after  MPI_Finalize  <#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	<#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on a window or file, acts as if MPI_Abort <#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	 <#mpi-comm-create-errhandler>	   then	    MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	<#mpi-file-create-errhandler>	  then	   MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

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

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

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

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				      MPI_FILE_SET_SIZE(3)
