SETLOCALE(3) Linux Programmer's Manual SETLOCALE(3)
setlocale - set the current locale
char *setlocale(int category, const char *locale);
The setlocale() function is used to set or query the program's current
If locale is not NULL, the program's current locale is modified accord-
ing to the arguments. The argument category determines which parts of
the program's current locale should be modified.
LC_ALL All of the locale
LC_ADDRESS Formatting of addresses and
geography-related items (*)
LC_COLLATE String collation
LC_CTYPE Character classification
LC_IDENTIFICATION Metadata describing the locale (*)
LC_MEASUREMENT Settings related to measurements
(metric versus US customary) (*)
LC_MESSAGES Localizable natural-language messages
LC_MONETARY Formatting of monetary values
LC_NAME Formatting of salutations for persons (*)
LC_NUMERIC Formatting of nonmonetary numeric values
LC_PAPER Settings related to the standard paper size (*)
LC_TELEPHONE Formats to be used with telephone services (*)
LC_TIME Formatting 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
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 cate-
gory), the environment variable LC_ALL is inspected, next the environ-
ment variable with the same name as the category (see the table above),
and finally the environment variable LANG. The first existing environ-
ment variable is used. If its value is not a valid locale specifica-
tion, the locale is unchanged, and setlocale() returns NULL.
The locale "C" or "POSIX" is a portable locale; it exists on all con-
A locale name is typically of the form language[_territory][.code-
set][@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:
after program initialization, by using the values returned from a
localeconv(3) call for locale-dependent information, by using the
multibyte and wide character functions for text processing if
MB_CUR_MAX > 1, and by using strcoll(3), wcscoll(3) or strxfrm(3),
wcsxfrm(3) to compare strings.
A successful call to setlocale() returns an opaque string that corre-
sponds to the locale set. This string may be allocated in static stor-
age. 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
For an explanation of the terms used in this section, see
|Interface | Attribute | Value |
|setlocale() | Thread safety | MT-Unsafe const:locale env |
POSIX.1-2001, POSIX.1-2008, C89, 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_MES-
SAGES. The remaining categories are GNU extensions.
locale(1), localedef(1), isalpha(3), localeconv(3), nl_langinfo(3),
rpmatch(3), strcoll(3), strftime(3), charsets(7), locale(7)
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