---
name: "fseek"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/fseek"
---

# fseek(3)

reposition a stream

## NAME

fgetpos, fseek, fsetpos, ftell, rewind - reposition a stream

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <stdio.h>
```

**int fseek(FILE \****stream***, long** *offset***, int** *whence***);** **long ftell(FILE \****stream***);**

**void rewind(FILE \****stream***);**

**int fgetpos(FILE \*restrict** *stream***, fpos\_t \*restrict** *pos***);** **int fsetpos(FILE \****stream***, const fpos\_t \****pos***);**

## DESCRIPTION

The **fseek**() function sets the file position indicator for the stream pointed to by *stream*. The new position, measured in bytes, is obtained by adding *offset* bytes to the position specified by *whence*. If *whence* is set to **SEEK\_SET**, **SEEK\_CUR**, or **SEEK\_END**, the offset is relative to the start of the file, the current position indicator, or end-of-file, respectively. A successful call to the **fseek**() function clears the end-of-file indicator for the stream and undoes any effects of the [**ungetc**(3)](/ungetc/3.md) function on the same stream.

The **ftell**() function obtains the current value of the file position indicator for the stream pointed to by *stream*.

The **rewind**() function sets the file position indicator for the stream pointed to by *stream* to the beginning of the file. It is equivalent to:

(void) fseek(stream, 0L, SEEK\_SET)

except that the error indicator for the stream is also cleared (see [**clearerr**(3)](/clearerr/3.md)).

The **fgetpos**() and **fsetpos**() functions are alternate interfaces equivalent to **ftell**() and **fseek**() (with *whence* set to **SEEK\_SET**), setting and storing the current value of the file offset into or from the object referenced by *pos*. On some non-UNIX systems, an *fpos\_t* object may be a complex object and these routines may be the only way to portably reposition a text stream.

If the stream refers to a regular file and the resulting stream offset is beyond the size of the file, subsequent writes will extend the file with a hole, up to the offset, before committing any data. See [**lseek**(2)](/lseek/2.md) for details on file seeking semantics.

## RETURN VALUE

The **rewind**() function returns no value. Upon successful completion, **fgetpos**(), **fseek**(), **fsetpos**() return 0, and **ftell**() returns the current offset. Otherwise, -1 is returned and *errno* is set to indicate the error.

## ERRORS

- **EINVAL**

  The *whence* argument to **fseek**() was not **SEEK\_SET**, **SEEK\_END**, or **SEEK\_CUR**. Or: the resulting file offset would be negative.

- **ESPIPE**

  The file descriptor underlying *stream* is not seekable (e.g., it refers to a pipe, FIFO, or socket).

The functions **fgetpos**(), **fseek**(), **fsetpos**(), and **ftell**() may also fail and set *errno* for any of the errors specified for the routines [**fflush**(3)](/fflush/3.md), [**fstat**(2)](/fstat/2.md), [**lseek**(2)](/lseek/2.md), and [**malloc**(3)](/malloc/3.md).

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **fseek**(), **ftell**(), **rewind**(), **fgetpos**(), **fsetpos**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

POSIX.1-2001, C89.

## SEE ALSO

[**lseek**(2)](/lseek/2.md), [**fseeko**(3)](/fseeko/3.md)