char *nl_langinfo(ln_item ITEM);
nl_langinfo() 用于访问 locale 中的细节，粒度细，速度快。 其中， ITEM 定义在头文件 langinfo.h 中，解释如下：
`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 (*note 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.
