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

# fseeko(3)

seek to or report file position

## NAME

fseeko, ftello - seek to or report file position

## LIBRARY

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

## SYNOPSIS

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

**int fseeko(FILE \****stream***, off\_t** *offset***, int** *whence***);** **off\_t ftello(FILE \****stream***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**fseeko**(), **ftello**():

```
    _FILE_OFFSET_BITS == 64 || _POSIX_C_SOURCE >= 200112L
```

## DESCRIPTION

The **fseeko**() and **ftello**() functions are identical to [**fseek**(3)](/fseek/3.md) and [**ftell**(3)](/ftell/3.md) (see [**fseek**(3)](/fseek/3.md)), respectively, except that the *offset* argument of **fseeko**() and the return value of **ftello**() is of type *off\_t* instead of *long*.

On some architectures, both *off\_t* and *long* are 32-bit types, but defining **\_FILE\_OFFSET\_BITS** with the value 64 (before including *any* header files) will turn *off\_t* into a 64-bit type.

## RETURN VALUE

On successful completion, **fseeko**() returns 0, while **ftello**() returns the current offset. Otherwise, -1 is returned and *errno* is set to indicate the error.

## ERRORS

See the ERRORS in [**fseek**(3)](/fseek/3.md).

## ATTRIBUTES

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

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **fseeko**(), **ftello**() | Thread safety | MT-Safe |

## STANDARDS

POSIX.1-2008.

## HISTORY

glibc 2.1. POSIX.1-2001, SUSv2.

## NOTES

The declarations of these functions can also be obtained by defining the obsolete **\_LARGEFILE\_SOURCE** feature test macro.

## SEE ALSO

[**fseek**(3)](/fseek/3.md)