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.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH uselocale 3 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
uselocale \- set/get the locale for the calling thread
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <locale.h>
.P
.BI "locale_t uselocale(locale_t " newloc );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR uselocale ():
.nf
Since glibc 2.10:
_XOPEN_SOURCE >= 700
Before glibc 2.10:
_GNU_SOURCE
.fi
.SH DESCRIPTION
The
.BR uselocale ()
function sets the current locale for the calling thread,
and returns the thread's previously current locale.
After a successful call to
.BR uselocale (),
any calls by this thread to functions that depend on the locale
will operate as though the locale has been set to
.IR newloc .
.P
The
.I newloc
argument can have one of the following values:
.TP
A handle returned by a call to
.BR newlocale (3)
or
.BR duplocale (3)
The calling thread's current locale is set to the specified locale.
.TP
The special locale object handle
.B LC_GLOBAL_LOCALE
The calling thread's current locale is set to the global locale determined by
.BR setlocale (3).
.TP
.I "(locale_t) 0"
The calling thread's current locale is left unchanged
(and the current locale is returned as the function result).
.SH RETURN VALUE
On success,
.BR uselocale ()
returns the locale handle that was set by the previous call to
.BR uselocale ()
in this thread, or
.B LC_GLOBAL_LOCALE
if there was no such previous call.
On error, it returns
.IR "(locale_t)\ 0" ,
and sets
.I errno
to indicate the error.
.SH ERRORS
.TP
.B EINVAL
.I newloc
does not refer to a valid locale object.
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
glibc 2.3.
POSIX.1-2008.
.SH NOTES
Unlike
.BR setlocale (3),
.BR 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
.BR duplocale (3)
and
.BR newlocale (3)
to obtain a locale object equivalent to the current locale and
modify the desired categories in that object.
.SH EXAMPLES
See
.BR newlocale (3)
and
.BR duplocale (3).
.SH SEE ALSO
.BR locale (1),
.BR duplocale (3),
.BR freelocale (3),
.BR newlocale (3),
.BR setlocale (3),
.BR locale (5),
.BR locale (7)
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