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 extensions to the locale API
POSIX.1-2008 standardized a number of extensions to the locale
API, based on implementations that first appeared in version 2.3
of the GNU C library. 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.
