setlocale - Man Page

set the current locale


Standard C library (libc, -lc)


#include <locale.h>

char *setlocale(int category, const char *locale);


The setlocale() function is used to set or query the program's current locale.

If locale is not NULL, the program's current locale is modified according to the arguments. The argument category determines which parts of the program's current locale should be modified.

LC_ALLAll of the locale
LC_ADDRESSFormatting of addresses and geography-related items (*)
LC_COLLATEString collation
LC_CTYPECharacter classification
LC_IDENTIFICATIONMetadata describing the locale (*)
LC_MEASUREMENTSettings related to measurements (metric versus US customary) (*)
LC_MESSAGESLocalizable natural-language messages
LC_MONETARYFormatting of monetary values
LC_NAMEFormatting of salutations for persons (*)
LC_NUMERICFormatting of nonmonetary numeric values
LC_PAPERSettings related to the standard paper size (*)
LC_TELEPHONEFormats to be used with telephone services (*)
LC_TIMEFormatting of date and time values

The categories marked with an asterisk in the above table are GNU extensions. For further information on these locale categories, see locale(7).

The argument locale is a pointer to a character string containing the required setting of category. Such a string is either a well-known constant like "C" or "da_DK" (see below), or an opaque string that was returned by another call of setlocale().

If locale is an empty string, "", each part of the locale that should be modified is set according to the environment variables. The details are implementation-dependent. For glibc, first (regardless of category), the environment variable LC_ALL is inspected, next the environment variable with the same name as the category (see the table above), and finally the environment variable LANG. The first existing environment variable is used. If its value is not a valid locale specification, the locale is unchanged, and setlocale() returns NULL.

The locale "C" or "POSIX" is a portable locale; it exists on all conforming systems.

A locale name is typically of the form language[_territory][.codeset][@modifier], where language is an ISO 639 language code, territory is an ISO 3166 country code, and codeset is a character set or encoding identifier like ISO-8859-1 or UTF-8. For a list of all supported locales, try "locale -a" (see locale(1)).

If locale is NULL, the current locale is only queried, not modified.

On startup of the main program, the portable "C" locale is selected as default. A program may be made portable to all locales by calling:

setlocale(LC_ALL, "");

after program initialization, and then:

Return Value

A successful call to setlocale() returns an opaque string that corresponds to the locale set. This string may be allocated in static storage. The string returned is such that a subsequent call with that string and its associated category will restore that part of the process's locale. The return value is NULL if the request cannot be honored.


For an explanation of the terms used in this section, see attributes(7).

setlocale()Thread safetyMT-Unsafe const:locale env


POSIX.1-2001, POSIX.1-2008, C99.

The C standards specify only the categories LC_ALL, LC_COLLATE, LC_CTYPE, LC_MONETARY, LC_NUMERIC, and LC_TIME. POSIX.1 adds LC_MESSAGES. The remaining categories are GNU extensions.

See Also

locale(1), localedef(1), isalpha(3), localeconv(3), nl_langinfo(3), rpmatch(3), strcoll(3), strftime(3), charsets(7), locale(7)

Referenced By, brlapi_write(3), catgets(3), catopen(3), duplocale(3), ecvt(3), editline(3), flatpak-config(1), getdate(3), gettext(3), groffer(1), html2ps(1), html2psrc(5), isalpha(3), locale(5), locale(7), localeconv(3), localedef(1), lsof(1), lynx(1),, mksh(1), mkvmerge(1), ncurses.3x(3), newlocale(3), nl_langinfo(3), notcurses_direct(3), notcurses_init(3), notcurses_metric(3), pam_sss(8), perlapi(1), perllocale(1), printf(3), procenv(1), rpmatch(3), s-nail(1), sscanf(3), strcoll(3), strfmon(3), strftime(3), strptime(3), strxfrm(3), tcsh(1), toupper(3), trader(6), tuxpaint(1), unicode(7), uselocale(3), utf-8(7),, xterm(1).

2023-02-05 Linux man-pages 6.03