localeconv() 同 setlocale() 一样，是由标准 C 提供的，可移植， 但使用代价昂贵，可拓展性差。并且，它接提供了访问 locale 中的 LC_MONETARY 和 LC_NUMERIC ， 通用性差。

localeconv() 原型为：

struct lconv * localeconv (void);

该函数返回一个 lconv 结构的指针， lconv 结构中的元素包含了如何在当前 locale 中格式化输出数字和货币的一些信息。 Glibc 中，其定义如下：

/* Structure giving information about numeric and monetary notation.  */
struct lconv
{
  /* Numeric (non-monetary) information.  */

  char *decimal_point;      /* Decimal point character.  */
  char *thousands_sep;      /* Thousands separator.  */
  /* Each element is the number of digits in each group;
     elements with higher indices are farther 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 farther left.  */
  char *grouping;

  /* Monetary information.  */

  /* First three chars are a currency symbol from ISO 4217.
     Fourth char is the separator.  Fifth char is '\0'.  */
  char *int_curr_symbol;
  char *currency_symbol;    /* Local currency symbol.  */
  char *mon_decimal_point;  /* Decimal point character.  */
  char *mon_thousands_sep;  /* Thousands separator.  */
  char *mon_grouping;       /* Like `grouping' element (above).  */
  char *positive_sign;      /* Sign for positive values.  */
  char *negative_sign;      /* Sign for negative values.  */
  char int_frac_digits;     /* Int'l fractional digits.  */
  char frac_digits;     /* Local fractional digits.  */
  /* 1 if currency_symbol precedes a positive value, 0 if succeeds.  */
  char p_cs_precedes;
  /* 1 iff a space separates currency_symbol from a positive value.  */
  char p_sep_by_space;
  /* 1 if currency_symbol precedes a negative value, 0 if succeeds.  */
  char n_cs_precedes;
  /* 1 iff a space separates currency_symbol from a negative value.  */
  char n_sep_by_space;
  /* 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 follows the quantity and currency_symbol.
     3 The sign string immediately precedes the currency_symbol.
     4 The sign string immediately follows the currency_symbol.  */
  char p_sign_posn;
  char n_sign_posn;
#ifdef __USE_ISOC99
  /* 1 if int_curr_symbol precedes a positive value, 0 if succeeds.  */
  char int_p_cs_precedes;
  /* 1 iff a space separates int_curr_symbol from a positive value.  */
  char int_p_sep_by_space;
  /* 1 if int_curr_symbol precedes a negative value, 0 if succeeds.  */
  char int_n_cs_precedes;
  /* 1 iff a space separates int_curr_symbol from a negative value.  */
  char int_n_sep_by_space;
  /* Positive and negative sign positions:
     0 Parentheses surround the quantity and int_curr_symbol.
     1 The sign string precedes the quantity and int_curr_symbol.
     2 The sign string follows the quantity and int_curr_symbol.
     3 The sign string immediately precedes the int_curr_symbol.
     4 The sign string immediately follows the int_curr_symbol.  */
  char int_p_sign_posn;
  char int_n_sign_posn;
#else
  char __int_p_cs_precedes;
  char __int_p_sep_by_space;
  char __int_n_cs_precedes;
  char __int_n_sep_by_space;
  char __int_p_sign_posn;
  char __int_n_sign_posn;
#endif
};

具体含义，参考其中注释。

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.