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

# uselocale(3p)

use locale in current thread

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

## NAME

uselocale — use locale in current thread

## SYNOPSIS

```
#include <locale.h>
```

locale\_t uselocale(locale\_t *newloc*);

## DESCRIPTION

The *uselocale*() function shall set or query the current locale for the calling thread.

The value for the *newloc* argument shall be one of the following:

- 1\.

  A value returned by the *newlocale*() or *duplocale*() functions

- 2\.

  The special locale object descriptor LC\_GLOBAL\_LOCALE

- 3\.

  (**locale\_t**)0

If the *newloc* argument is (**locale\_t**)0, the current locale shall not be changed; this value can be used to query the current locale setting. If the *newloc* argument is LC\_GLOBAL\_LOCALE, any thread-local locale for the calling thread shall be uninstalled; the thread shall again use the global locale as the current locale, and changes to the global locale shall affect the thread. Otherwise, the locale represented by *newloc* shall be installed as a thread-local locale to be used as the current locale for the calling thread.

Once the *uselocale*() function has been called to install a thread-local locale, the behavior of every interface using data from the current locale shall be affected for the calling thread. The current locale for other threads shall remain unchanged.

## RETURN VALUE

Upon successful completion, the *uselocale*() function shall return a handle for the thread-local locale that was in use as the current locale for the calling thread on entry to the function, or LC\_GLOBAL\_LOCALE if no thread-local locale was in use. Otherwise, *uselocale*() shall return (**locale\_t**)0 and set *errno* to indicate the error.

## ERRORS

The *uselocale*() function may fail if:

- **EINVAL**

  *newloc* is not a valid locale object and is not (**locale\_t**)0.

*The following sections are informative.*

## EXAMPLES

None.

## APPLICATION USAGE

Unlike the *setlocale*() function, the *uselocale*() function does not allow replacing some locale categories only. Applications that need to install a locale which differs only in a few categories must use *newlocale*() to change a locale object equivalent to the currently used locale and install it.

## RATIONALE

None.

## FUTURE DIRECTIONS

None.

## SEE ALSO

*duplocale()*, *freelocale()*, *newlocale()*, *setlocale()*

The Base Definitions volume of POSIX.1‐2017, ***\<locale.h\>***

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting\_bugs.html .