---
name: "uselocale"
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/uselocale"
---

# uselocale(3)

set/get the locale for the calling thread

## NAME

uselocale - set/get the locale for the calling thread

## LIBRARY

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

## SYNOPSIS

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

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

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

**uselocale**():

```
    Since glibc 2.10:
        _XOPEN_SOURCE >= 700
    Before glibc 2.10:
        _GNU_SOURCE
```

## DESCRIPTION

The **uselocale**() function sets the current locale for the calling thread, and returns the thread's previously current locale. After a successful call to **uselocale**(), any calls by this thread to functions that depend on the locale will operate as though the locale has been set to *newloc*.

The *newloc* argument can have one of the following values:

- A handle returned by a call to

  [**newlocale**(3)](/newlocale/3.md) or [**duplocale**(3)](/duplocale/3.md) The calling thread's current locale is set to the specified locale.

- The special locale object handle

  **LC\_GLOBAL\_LOCALE** The calling thread's current locale is set to the global locale determined by [**setlocale**(3)](/setlocale/3.md).

- *(locale\_t) 0*

  The calling thread's current locale is left unchanged (and the current locale is returned as the function result).

## RETURN VALUE

On success, **uselocale**() returns the locale handle that was set by the previous call to **uselocale**() in this thread, or **LC\_GLOBAL\_LOCALE** if there was no such previous call. On error, it returns *(locale\_t) 0*, and sets *errno* to indicate the error.

## ERRORS

- **EINVAL**

  *newloc* does not refer to a valid locale object.

## STANDARDS

POSIX.1-2008.

## HISTORY

glibc 2.3. POSIX.1-2008.

## NOTES

Unlike [**setlocale**(3)](/setlocale/3.md), **uselocale**() does not allow selective replacement of individual locale categories. To employ a locale that differs in only a few categories from the current locale, use calls to [**duplocale**(3)](/duplocale/3.md) and [**newlocale**(3)](/newlocale/3.md) to obtain a locale object equivalent to the current locale and modify the desired categories in that object.

## EXAMPLES

See [**newlocale**(3)](/newlocale/3.md) and [**duplocale**(3)](/duplocale/3.md).

## SEE ALSO

[**locale**(1)](/locale/1.md), [**duplocale**(3)](/duplocale/3.md), [**freelocale**(3)](/freelocale/3.md), [**newlocale**(3)](/newlocale/3.md), [**setlocale**(3)](/setlocale/3.md), [**locale**(5)](/locale/5.md), [**locale**(7)](/locale/7.md)