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.

uselocale — use locale in current thread

#include <locale.h>
locale_t uselocale(locale_t newloc);

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:

A value returned by the newlocale() or duplocale() functions
The special locale object descriptor LC_GLOBAL_LOCALE

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.

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.

The uselocale() function may fail if:

newloc is not a valid locale object and is not (locale_t)0.

The following sections are informative.


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.



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

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

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 .

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2017 IEEE/The Open Group