---
name: "fileno"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/clearerr"
---

# fileno(3)

check and reset stream status

Part of [clearerr(3)](/clearerr/3.md).

## NAME

**clearerr**, **clearerr\_unlocked**, **feof**, **feof\_unlocked**, **ferror**, **ferror\_unlocked**, **fileno**, **fileno\_unlocked** – check and reset stream status

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<stdio.h\>**

*void*\

**clearerr**(*FILE \*stream*);

*void*\

**clearerr\_unlocked**(*FILE \*stream*);

*int*\

**feof**(*FILE \*stream*);

*int*\

**feof\_unlocked**(*FILE \*stream*);

*int*\

**ferror**(*FILE \*stream*);

*int*\

**ferror\_unlocked**(*FILE \*stream*);

*int*\

**fileno**(*FILE \*stream*);

*int*\

**fileno\_unlocked**(*FILE \*stream*);

## DESCRIPTION

The function **clearerr**() clears the end-of-file and error indicators for the stream pointed to by *stream*.

The function **feof**() tests the end-of-file indicator for the stream pointed to by *stream*, returning non-zero if it is set. The end-of-file indicator may be cleared by explicitly calling **clearerr**(), or as a side-effect of other operations, e.g. **fseek**().

The function **ferror**() tests the error indicator for the stream pointed to by *stream*, returning non-zero if it is set.

The function **fileno**() examines the argument *stream* and returns its integer descriptor.

The **clearerr\_unlocked**(), **feof\_unlocked**(), **ferror\_unlocked**(), and **fileno\_unlocked**() functions are equivalent to **clearerr**(), **feof**(), **ferror**(), and **fileno**() respectively, except that the caller is responsible for locking the stream with [flockfile(3)](/flockfile/3.md) before calling them. These functions may be used to avoid the overhead of locking the stream and to prevent races when multiple threads are operating on the same stream.

## ERRORS

These functions, except **fileno**(), should not fail and do not set the external variable *errno*.

On error, **fileno**() returns -1 and sets *errno* to one of the following values:

- \[EBADF\]

  The stream is not associated with a file.

- \[EBADF\]

  The file descriptor underlying stream is not a valid file descriptor.

  Note that detection of this condition is not reliable, the error might be not reported.

## SEE ALSO

[open(2)](/open/2.md), [fdopen(3)](/fdopen/3.md), [flockfile(3)](/flockfile/3.md), [stdio(3)](/stdio/3.md)

## STANDARDS

The functions **clearerr**(), **feof**(), and **ferror**() conform to ISO/IEC 9899:1990 (“ISO C90”).

## HISTORY

The functions **clearerr**(), **feof**(), **ferror**(), and **fileno**() first appeared in Version 7 AT&T UNIX.