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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022

uselocale (3C)


uselocale - use locale in current thread


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


The uselocale() function sets 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 is not 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 is uninstalled. The thread again use the global locale as the current locale, and changes to the global locale affects the thread. Otherwise, the locale represented by newloc is 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 is affected for the calling thread. The current locale for other threads remains unchanged.

Return Values

Upon successful completion, the uselocale() function returns 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() return (locale_t)0 and set errno to indicate the error.


The uselocale() function will fail if:


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


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.


See attributes(7) for descriptions of the following attributes:

Interface Stability

See Also

duplocale(3C), freelocale(3C), newlocale(3C), attributes(7), standards(7)