---
name: "MPI_File_set_size.openmpi"
section: "3"
platform: "linux"
package: "openmpi-doc"
version: "5.0.7-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/MPI_File_set_size.openmpi"
---

# MPI\_File\_set\_size.openmpi(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* 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\_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