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Pinpoint Access to Locale Data
When writing the X/Open Portability Guide the authors realized that the
localeconv
function is not enough to provide reasonable access to
locale information. The information which was meant to be available
in the locale (as later specified in the POSIX.1 standard) requires more
ways to access it. Therefore the nl_langinfo
function
was introduced.
char * nl_langinfo (nl_item item)
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Function |
The nl_langinfo function can be used to access individual
elements of the locale categories. Unlike the localeconv
function, which returns all the information, nl_langinfo
lets the caller select what information it requires. This is very
fast and it is not a problem to call this function multiple times.
A second advantage is that in addition to the numeric and monetary
formatting information, information from the
LC_TIME and LC_MESSAGES categories is available.
The type nl_type is defined in nl_types.h . The argument
item is a numeric value defined in the header langinfo.h .
The X/Open standard defines the following values:
CODESET
nl_langinfo returns a string with the name of the coded character
set used in the selected locale.
ABDAY_1
ABDAY_2
ABDAY_3
ABDAY_4
ABDAY_5
ABDAY_6
ABDAY_7
nl_langinfo returns the abbreviated weekday name. ABDAY_1
corresponds to Sunday.
DAY_1
DAY_2
DAY_3
DAY_4
DAY_5
DAY_6
DAY_7
- Similar to
ABDAY_1 etc., but here the return value is the
unabbreviated weekday name.
ABMON_1
ABMON_2
ABMON_3
ABMON_4
ABMON_5
ABMON_6
ABMON_7
ABMON_8
ABMON_9
ABMON_10
ABMON_11
ABMON_12
- The return value is abbreviated name of the month.
ABMON_1
corresponds to January.
MON_1
MON_2
MON_3
MON_4
MON_5
MON_6
MON_7
MON_8
MON_9
MON_10
MON_11
MON_12
- Similar to
ABMON_1 etc., but here the month names are not abbreviated.
Here the first value MON_1 also corresponds to January.
AM_STR
PM_STR
- The return values are strings which can be used in the representation of time
as an hour from 1 to 12 plus an am/pm specifier.
Note that in locales which do not use this time representation
these strings might be empty, in which case the am/pm format
cannot be used at all.
D_T_FMT
- The return value can be used as a format string for
strftime to
represent time and date in a locale-specific way.
D_FMT
- The return value can be used as a format string for
strftime to
represent a date in a locale-specific way.
T_FMT
- The return value can be used as a format string for
strftime to
represent time in a locale-specific way.
T_FMT_AMPM
- The return value can be used as a format string for
strftime to
represent time in the am/pm format.
Note that if the am/pm format does not make any sense for the
selected locale, the return value might be the same as the one for
T_FMT .
ERA
- The return value represents the era used in the current locale.
Most locales do not define this value. An example of a locale which
does define this value is the Japanese one. In Japan, the traditional
representation of dates includes the name of the era corresponding to
the then-emperor's reign.
Normally it should not be necessary to use this value directly.
Specifying the E modifier in their format strings causes the
strftime functions to use this information. The format of the
returned string is not specified, and therefore you should not assume
knowledge of it on different systems.
ERA_YEAR
- The return value gives the year in the relevant era of the locale.
As for
ERA it should not be necessary to use this value directly.
ERA_D_T_FMT
- This return value can be used as a format string for
strftime to
represent dates and times in a locale-specific era-based way.
ERA_D_FMT
- This return value can be used as a format string for
strftime to
represent a date in a locale-specific era-based way.
ERA_T_FMT
- This return value can be used as a format string for
strftime to
represent time in a locale-specific era-based way.
ALT_DIGITS
- The return value is a representation of up to 100 values used to
represent the values 0 to 99. As for
ERA this
value is not intended to be used directly, but instead indirectly
through the strftime function. When the modifier O is
used in a format which would otherwise use numerals to represent hours,
minutes, seconds, weekdays, months, or weeks, the appropriate value for
the locale is used instead.
INT_CURR_SYMBOL
- The same as the value returned by
localeconv in the
int_curr_symbol element of the struct lconv .
CURRENCY_SYMBOL
CRNCYSTR
- The same as the value returned by
localeconv in the
currency_symbol element of the struct lconv .
CRNCYSTR is a deprecated alias still required by Unix98.
MON_DECIMAL_POINT
- The same as the value returned by
localeconv in the
mon_decimal_point element of the struct lconv .
MON_THOUSANDS_SEP
- The same as the value returned by
localeconv in the
mon_thousands_sep element of the struct lconv .
MON_GROUPING
- The same as the value returned by
localeconv in the
mon_grouping element of the struct lconv .
POSITIVE_SIGN
- The same as the value returned by
localeconv in the
positive_sign element of the struct lconv .
NEGATIVE_SIGN
- The same as the value returned by
localeconv in the
negative_sign element of the struct lconv .
INT_FRAC_DIGITS
- The same as the value returned by
localeconv in the
int_frac_digits element of the struct lconv .
FRAC_DIGITS
- The same as the value returned by
localeconv in the
frac_digits element of the struct lconv .
P_CS_PRECEDES
- The same as the value returned by
localeconv in the
p_cs_precedes element of the struct lconv .
P_SEP_BY_SPACE
- The same as the value returned by
localeconv in the
p_sep_by_space element of the struct lconv .
N_CS_PRECEDES
- The same as the value returned by
localeconv in the
n_cs_precedes element of the struct lconv .
N_SEP_BY_SPACE
- The same as the value returned by
localeconv in the
n_sep_by_space element of the struct lconv .
P_SIGN_POSN
- The same as the value returned by
localeconv in the
p_sign_posn element of the struct lconv .
N_SIGN_POSN
- The same as the value returned by
localeconv in the
n_sign_posn element of the struct lconv .
INT_P_CS_PRECEDES
- The same as the value returned by
localeconv in the
int_p_cs_precedes element of the struct lconv .
INT_P_SEP_BY_SPACE
- The same as the value returned by
localeconv in the
int_p_sep_by_space element of the struct lconv .
INT_N_CS_PRECEDES
- The same as the value returned by
localeconv in the
int_n_cs_precedes element of the struct lconv .
INT_N_SEP_BY_SPACE
- The same as the value returned by
localeconv in the
int_n_sep_by_space element of the struct lconv .
INT_P_SIGN_POSN
- The same as the value returned by
localeconv in the
int_p_sign_posn element of the struct lconv .
INT_N_SIGN_POSN
- The same as the value returned by
localeconv in the
int_n_sign_posn element of the struct lconv .
DECIMAL_POINT
RADIXCHAR
- The same as the value returned by
localeconv in the
decimal_point element of the struct lconv .
The name RADIXCHAR is a deprecated alias still used in Unix98.
THOUSANDS_SEP
THOUSEP
- The same as the value returned by
localeconv in the
thousands_sep element of the struct lconv .
The name THOUSEP is a deprecated alias still used in Unix98.
GROUPING
- The same as the value returned by
localeconv in the
grouping element of the struct lconv .
YESEXPR
- The return value is a regular expression which can be used with the
regex function to recognize a positive response to a yes/no
question. The GNU C library provides the rpmatch function for
easier handling in applications.
NOEXPR
- The return value is a regular expression which can be used with the
regex function to recognize a negative response to a yes/no
question.
YESSTR
- The return value is a locale-specific translation of the positive response
to a yes/no question.
Using this value is deprecated since it is a very special case of
message translation, and is better handled by the message
translation functions (see Message Translation).
The use of this symbol is deprecated. Instead message translation
should be used.
NOSTR
- The return value is a locale-specific translation of the negative response
to a yes/no question. What is said for
YESSTR is also true here.
The use of this symbol is deprecated. Instead message translation
should be used.
The file langinfo.h defines a lot more symbols but none of them
is official. Using them is not portable, and the format of the
return values might change. Therefore we recommended you not use
them.
Note that the return value for any valid argument can be used for
in all situations (with the possible exception of the am/pm time formatting
codes). If the user has not selected any locale for the
appropriate category, nl_langinfo returns the information from the
"C" locale. It is therefore possible to use this function as
shown in the example below.
If the argument item is not valid, a pointer to an empty string is
returned.
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An example of nl_langinfo
usage is a function which has to
print a given date and time in a locale-specific way. At first one
might think that, since strftime
internally uses the locale
information, writing something like the following is enough:
size_t
i18n_time_n_data (char *s, size_t len, const struct tm *tp)
{
return strftime (s, len, "%X %D", tp);
}
The format contains no weekday or month names and therefore is
internationally usable. Wrong! The output produced is something like
"hh:mm:ss MM/DD/YY"
. This format is only recognizable in the
USA. Other countries use different formats. Therefore the function
should be rewritten like this:
size_t
i18n_time_n_data (char *s, size_t len, const struct tm *tp)
{
return strftime (s, len, nl_langinfo (D_T_FMT), tp);
}
Now it uses the date and time format of the locale
selected when the program runs. If the user selects the locale
correctly there should never be a misunderstanding over the time and
date format.