---
name: "fwide"
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/fwide"
---

# fwide(3)

set and determine the orientation of a FILE stream

## NAME

fwide - set and determine the orientation of a FILE stream

## LIBRARY

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

## SYNOPSIS

```
#include <wchar.h>
```

**int fwide(FILE \****stream***, int** *mode***);**

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

**fwide**():

```
    _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE
        || _POSIX_C_SOURCE >= 200112L
```

## DESCRIPTION

When *mode* is zero, the **fwide**() function determines the current orientation of *stream*. It returns a positive value if *stream* is wide-character oriented, that is, if wide-character I/O is permitted but char I/O is disallowed. It returns a negative value if *stream* is byte oriented—that is, if char I/O is permitted but wide-character I/O is disallowed. It returns zero if *stream* has no orientation yet; in this case the next I/O operation might change the orientation (to byte oriented if it is a char I/O operation, or to wide-character oriented if it is a wide-character I/O operation).

Once a stream has an orientation, it cannot be changed and persists until the stream is closed.

When *mode* is nonzero, the **fwide**() function first attempts to set *stream*'s orientation (to wide-character oriented if *mode* is greater than 0, or to byte oriented if *mode* is less than 0). It then returns a value denoting the current orientation, as above.

## RETURN VALUE

The **fwide**() function returns the stream's orientation, after possibly changing it. A positive return value means wide-character oriented. A negative return value means byte oriented. A return value of zero means undecided.

## STANDARDS

C11, POSIX.1-2008.

## HISTORY

POSIX.1-2001, C99.

## NOTES

Wide-character output to a byte oriented stream can be performed through the [**fprintf**(3)](/fprintf/3.md) function with the **%lc** and **%ls** directives.

Char oriented output to a wide-character oriented stream can be performed through the [**fwprintf**(3)](/fwprintf/3.md) function with the **%c** and **%s** directives.

## SEE ALSO

[**fprintf**(3)](/fprintf/3.md), [**fwprintf**(3)](/fwprintf/3.md)