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 locale.
If locale is not NULL, the program's current locale is modified according to the argu-
ments. The argument category determines which parts of the program's current locale
should be modified.
LC_ALL for all of the locale.
for regular expression matching (it determines the meaning of range expressions and
equivalence classes) and string collation.
for regular expression matching, character classification, conversion, case-sensi-
tive comparison, and wide character functions.
for localizable natural-language messages.
for monetary formatting.
for number formatting (such as the decimal point and the thousands separator).
for time and date formatting.
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 "", 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 environ-
ment variable with the same name as the category (LC_COLLATE, LC_CTYPE, LC_MESSAGES,
LC_MONETARY, LC_NUMERIC, LC_TIME) 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; its LC_CTYPE part corresponds to the 7-bit
ASCII character set.
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", cf. 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 ini-
tialization, by using the values returned from a localeconv() call for locale - dependent
information, by using the multi-byte and wide character functions for text processing if
MB_CUR_MAX > 1, and by using strcoll(), wcscoll() or strxfrm(), wcsxfrm() to compare
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.
ANSI C, POSIX.1
Linux (that is, GNU libc) supports the portable locales "C" and "POSIX". In the good old
days there used to be support for the European Latin-1 "ISO-8859-1" locale (e.g. in
libc-4.5.21 and libc-4.6.27), and the Russian "KOI-8" (more precisely, "koi-8r") locale
(e.g. in libc-4.6.27), so that having an environment variable LC_CTYPE=ISO-8859-1 sufficed
to make isprint() return the right answer. These days non-English speaking Europeans have
to work a bit harder, and must install actual locale files.
locale(1), localedef(1), strcoll(3), isalpha(3), localeconv(3), strftime(3), charsets(4),
GNU 1999-07-04 SETLOCALE(3)