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man pages section 3: Basic Library Functions

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Updated: Thursday, June 13, 2019
 
 

setlocale(3C)

Name

setlocale - modify and query global locale

Synopsis

#include <locale.h>

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

Description

The setlocale() function selects the appropriate piece of the global locale for the process as specified by the category and locale arguments. The category argument may have the following values: LC_CTYPE, LC_NUMERIC, LC_TIME, LC_COLLATE, LC_MONETARY, LC_MESSAGES, and LC_ALL. These names are defined in the <locale.h> header. The LC_ALL variable names all of the global locale categories.

The LC_CTYPE variable affects the behavior of character handling functions such as isdigit(3C) and tolower(3C), and multibyte character functions such as mbtowc(3C) and wctomb(3C).

The LC_NUMERIC variable affects the decimal point character and thousands separator character for the formatted input/output functions and string conversion functions.

The LC_TIME variable affects the date and time format as delivered by ascftime(3C), cftime(3C), getdate(3C), strftime(3C), and strptime(3C).

The LC_COLLATE variable affects the sort order produced by collating functions such as strcoll(3C) and strxfrm(3C).

The LC_MONETARY variable affects the monetary formatted information returned by localeconv(3C).

The LC_MESSAGES variable affects the behavior of messaging functions such as dgettext(3C), gettext(3C), and gettxt(3C).

A value of “C” for locale specifies the traditional UNIX system behavior. At program startup, the equivalent of

setlocale(LC_ALL, "C")

is executed. This has the effect of initializing global locale for each category to the locale described by the environment “C”.

A value of “” for locale specifies that the global locale should be taken from environment variables. The order in which the environment variables are checked for the various categories is given below:

Category
1st Env Var
2nd Env Var
3rd Env Var
LC_CTYPE:
LC_ALL
LC_CTYPE
LANG
LC_COLLATE:
LC_ALL
LC_COLLATE
LANG
LC_TIME:
LC_ALL
LC_TIME
LANG
LC_NUMERIC:
LC_ALL
LC_NUMERIC
LANG
LC_MONETARY:
LC_ALL
LC_MONETARY
LANG
LC_MESSAGES:
LC_ALL
LC_MESSAGES
LANG

If a pointer to a string is given for locale, setlocale() attempts to set the global locale for the given category to locale. If setlocale() succeeds, locale is returned. If setlocale() fails, a null pointer is returned and the global locale is not changed.

For category LC_ALL, the behavior is slightly different. If a pointer to a string is given for locale and LC_ALL is given for category, setlocale() attempts to set the global locale for all the categories to locale. The locale may be a simple locale, consisting of a single locale, or a composite locale. If the locales for all the categories are the same after all the attempted locale changes, setlocale() will return a pointer to the common simple locale. If there is a mixture of locales among the categories, setlocale() will return a composite locale.

A null pointer for locale directs setlocale() to query the current global locale setting and return a pointer to the string associated with the category for the current global locale. If the category is LC_ALL and the current global locale is a composite locale, the string will have locale names for LC_CTYPE, LC_NUMERIC, LC_TIME, LC_COLLATE, LC_MONETARY, and LC_MESSAGES categories, and in that order, concatenated together where each category's locale name is prefixed with a slash ('/' or 0x2F) character, for instance, "/en_US.UTF-8/C/C/C/C/C". Otherwise, the string will have a locale name such as "en_US.UTF-8".

Return Values

Upon successful completion, setlocale() returns the string associated with the specified category for the new locale. Otherwise, setlocale() returns a null pointer and the global locale is not changed.

A null pointer for locale causes setlocale() to return a pointer to the string associated with the category for the current global locale. The global locale is not changed.

The string returned by setlocale() is such that a subsequent call with that string and its associated category will restore that part of the global locale. The string returned must not be modified by the program, but may be overwritten by a subsequent call to setlocale().

Errors

No errors are defined.

Files

/usr/lib/locale/locale

locale database directory for locale

Attributes

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

ATTRIBUTE TYPE
ATTRIBUTE VALUE
CSI
Enabled
Interface Stability
Committed
MT-Level
MT-Safe with exceptions
Standard

See Also

locale(1), ctype(3C), duplocale(3C), freelocale(3C), getdate(3C), gettext(3C), gettxt(3C), isdigit(3C), localeconv(3C), locale_fallback(3C), localelist(3C), localelistfree(3C), mbtowc(3C), newlocale(3C), strcoll(3C), strftime(3C), strptime(3C), strxfrm(3C), tolower(3C), uselocale(3C), wctomb(3C), libc(3LIB), attributes(7), environ(7), locale(7), locale_alias(7), standards(7)

Notes

It is unsafe for any thread to change global locale (by calling setlocale() with a non-null locale argument) in a multithreaded application while any other thread in the application is using any locale-sensitive routine. To change global locale in a multithreaded application, setlocale() should be called prior to using any locale-sensitive routine. To change current locale, uselocale() should be called. Using setlocale() to query the current global locale is safe and can be used anywhere in a multithreaded application.

It is the user's responsibility to ensure that mixed locale categories are compatible. For example, setting LC_CTYPE=C and LC_TIME=ja (where ja indicates Japanese) will not work, because Japanese time cannot be represented in the “C” locale's ASCII codeset.

To get the list of installed locales, instead of calling setlocale() over a list of potentially installed locales and checking on the return values, using localelist(3C) is recommended. The localelist() function does not switch locales and it is more efficient, faster, and fully MT-safe.

If a string pointed by locale argument has a locale name that does not yield a usable locale in the current system but it is a locale name alias that is accepted and supported, such name is internally mapped to a corresponding canonical locale name which is then used to locate, load, and return the actual locale defined in the current system. If successful, the return value of the function is the locale name alias. If there is no actual locale for the canonical locale name, obviously, the setlocale() will fail. The accepted and supported locale name aliases are shown in locale_alias(7).