locale - description of multilanguage support
#include <locale.h>
A locale is a set of language and cultural rules. These cover aspects such as
language for messages, different character sets, lexicographic conventions,
and so on. A program needs to be able to determine its locale and act
accordingly to be portable to different cultures.
The header
<locale.h> declares data types, functions, and macros
which are useful in this task.
The functions it declares are
setlocale(3) to set the current locale, and
localeconv(3) to get information about number formatting.
There are different categories for locale information a program might need; they
are declared as macros. Using them as the first argument to the
setlocale(3) function, it is possible to set one of these to the
desired locale:
-
LC_ADDRESS (GNU extension, since glibc 2.2)
- Change settings that describe the formats (e.g., postal
addresses) used to describe locations and geography-related items.
Applications that need this information can use nl_langinfo(3) to
retrieve nonstandard elements, such as _NL_ADDRESS_COUNTRY_NAME
(country name, in the language of the locale) and
_NL_ADDRESS_LANG_NAME (language name, in the language of the
locale), which return strings such as "Deutschland" and
"Deutsch" (for German-language locales). (Other element names
are listed in <langinfo.h>.)
- LC_COLLATE
- This category governs the collation rules used for sorting
and regular expressions, including character equivalence classes and
multicharacter collating elements. This locale category changes the
behavior of the functions strcoll(3) and strxfrm(3), which
are used to compare strings in the local alphabet. For example, the German
sharp s is sorted as "ss".
- LC_CTYPE
- This category determines the interpretation of byte
sequences as characters (e.g., single versus multibyte characters),
character classifications (e.g., alphabetic or digit), and the behavior of
character classes. On glibc systems, this category also determines the
character transliteration rules for iconv(1) and iconv(3).
It changes the behavior of the character handling and classification
functions, such as isupper(3) and toupper(3), and the
multibyte character functions such as mblen(3) or
wctomb(3).
-
LC_IDENTIFICATION (GNU extension, since glibc
2.2)
- Change settings that relate to the metadata for the locale.
Applications that need this information can use nl_langinfo(3) to
retrieve nonstandard elements, such as _NL_IDENTIFICATION_TITLE
(title of this locale document) and _NL_IDENTIFICATION_TERRITORY
(geographical territory to which this locale document applies), which
might return strings such as "English locale for the USA" and
"USA". (Other element names are listed in
<langinfo.h>.)
- LC_MONETARY
- This category determines the formatting used for
monetary-related numeric values. This changes the information returned by
localeconv(3), which describes the way numbers are usually printed,
with details such as decimal point versus decimal comma. This information
is internally used by the function strfmon(3).
- LC_MESSAGES
- This category affects the language in which messages are
displayed and what an affirmative or negative answer looks like. The GNU C
library contains the gettext(3), ngettext(3), and
rpmatch(3) functions to ease the use of this information. The GNU
gettext family of functions also obey the environment variable
LANGUAGE (containing a colon-separated list of locales) if the
category is set to a valid locale other than "C". This
category also affects the behavior of catopen(3).
-
LC_MEASUREMENT (GNU extension, since glibc 2.2)
- Change the settings relating to the measurement system in
the locale (i.e., metric versus US customary units). Applications can use
nl_langinfo(3) to retrieve the nonstandard
_NL_MEASUREMENT_MEASUREMENT element, which returns a pointer to a
character that has the value 1 (metric) or 2 (US customary units).
-
LC_NAME (GNU extension, since glibc 2.2)
- Change settings that describe the formats used to address
persons. Applications that need this information can use
nl_langinfo(3) to retrieve nonstandard elements, such as
_NL_NAME_NAME_MR (general salutation for men) and
_NL_NAME_NAME_MS (general salutation for women) elements, which
return strings such as "Herr" and "Frau" (for
German-language locales). (Other element names are listed in
<langinfo.h>.)
- LC_NUMERIC
- This category determines the formatting rules used for
nonmonetary numeric values—for example, the thousands separator and
the radix character (a period in most English-speaking countries, but a
comma in many other regions). It affects functions such as
printf(3), scanf(3), and strtod(3). This information
can also be read with the localeconv(3) function.
-
LC_PAPER (GNU extension, since glibc 2.2)
- Change the settings relating to the dimensions of the
standard paper size (e.g., US letter versus A4). Applications that need
the dimensions can obtain them by using nl_langinfo(3) to retrieve
the nonstandard _NL_PAPER_WIDTH and _NL_PAPER_HEIGHT
elements, which return int values specifying the dimensions in
millimeters.
-
LC_TELEPHONE (GNU extension, since glibc 2.2)
- Change settings that describe the formats to be used with
telephone services. Applications that need this information can use
nl_langinfo(3) to retrieve nonstandard elements, such as
_NL_TELEPHONE_INT_PREFIX (international prefix used to call numbers
in this locale), which returns a string such as "49" (for
Germany). (Other element names are listed in
<langinfo.h>.)
- LC_TIME
- This category governs the formatting used for date and time
values. For example, most of Europe uses a 24-hour clock versus the
12-hour clock used in the United States. The setting of this category
affects the behavior of functions such as strftime(3) and
strptime(3).
- LC_ALL
- All of the above.
If the second argument to
setlocale(3) is an empty string,
"", for the default locale, it is determined using the
following steps:
- (1)
- If there is a non-null environment variable LC_ALL,
the value of LC_ALL is used.
- (2)
- If an environment variable with the same name as one of the
categories above exists and is non-null, its value is used for that
category.
- (3)
- If there is a non-null environment variable LANG,
the value of LANG is used.
Values about local numeric formatting is made available in a
struct lconv
returned by the
localeconv(3) function, which has the following
declaration:
struct lconv {
/* Numeric (nonmonetary) information */
char *decimal_point; /* Radix character */
char *thousands_sep; /* Separator for digit groups to left
of radix character */
char *grouping; /* Each element is the number of digits in
a group; elements with higher indices
are further left. An element with value
CHAR_MAX means that no further grouping
is done. An element with value 0 means
that the previous element is used for
all groups further left. */
/* Remaining fields are for monetary information */
char *int_curr_symbol; /* First three chars are a currency
symbol from ISO 4217. Fourth char
is the separator. Fifth char
is '\0'. */
char *currency_symbol; /* Local currency symbol */
char *mon_decimal_point; /* Radix character */
char *mon_thousands_sep; /* Like thousands_sep above */
char *mon_grouping; /* Like grouping above */
char *positive_sign; /* Sign for positive values */
char *negative_sign; /* Sign for negative values */
char int_frac_digits; /* International fractional digits */
char frac_digits; /* Local fractional digits */
char p_cs_precedes; /* 1 if currency_symbol precedes a
positive value, 0 if succeeds */
char p_sep_by_space; /* 1 if a space separates
currency_symbol from a positive
value */
char n_cs_precedes; /* 1 if currency_symbol precedes a
negative value, 0 if succeeds */
char n_sep_by_space; /* 1 if a space separates
currency_symbol from a negative
value */
/* Positive and negative sign positions:
0 Parentheses surround the quantity and currency_symbol.
1 The sign string precedes the quantity and currency_symbol.
2 The sign string succeeds the quantity and currency_symbol.
3 The sign string immediately precedes the currency_symbol.
4 The sign string immediately succeeds the currency_symbol. */
char p_sign_posn;
char n_sign_posn;
};
POSIX.1-2008 standardized a number of extensions to the locale API, based on
implementations that first appeared in glibc 2.3. These extensions are
designed to address the problem that the traditional locale APIs do not mix
well with multithreaded applications and with applications that must deal with
multiple locales.
The extensions take the form of new functions for creating and manipulating
locale objects (
newlocale(3),
freelocale(3),
duplocale(3), and
uselocale(3)) and various new library
functions with the suffix "_l" (e.g.,
toupper_l(3)) that
extend the traditional locale-dependent APIs (e.g.,
toupper(3)) to
allow the specification of a locale object that should apply when executing
the function.
The following environment variable is used by
newlocale(3) and
setlocale(3), and thus affects all unprivileged localized programs:
- LOCPATH
- A list of pathnames, separated by colons (':'), that should
be used to find locale data. If this variable is set, only the individual
compiled locale data files from LOCPATH and the system default
locale data path are used; any available locale archives are not used (see
localedef(1)). The individual compiled locale data files are
searched for under subdirectories which depend on the currently used
locale. For example, when en_GB.UTF-8 is used for a category, the
following subdirectories are searched for, in this order:
en_GB.UTF-8, en_GB.utf8, en_GB, en.UTF-8,
en.utf8, and en.
- /usr/lib/locale/locale-archive
- Usual default locale archive location.
- /usr/lib/locale
- Usual default path for compiled individual locale
files.
POSIX.1-2001.
iconv(1),
locale(1),
localedef(1),
catopen(3),
gettext(3),
iconv(3),
localeconv(3),
mbstowcs(3),
newlocale(3),
ngettext(3),
nl_langinfo(3),
rpmatch(3),
setlocale(3),
strcoll(3),
strfmon(3),
strftime(3),
strxfrm(3),
uselocale(3),
wcstombs(3),
locale(5),
charsets(7),
unicode(7),
utf-8(7)