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 local 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:


This is used to change 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".


This 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).


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).


changes the language messages are displayed in 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 these 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".


changes the information used by the printf(3) and scanf(3) family of functions, when they are advised to use the locale-settings. This information can also be read with the localeconv(3) function.


changes the behavior of the strftime(3) function to display the current time in a locally acceptable form; for example, most of Europe uses a 24-hour clock versus the 12-hour clock used in the United States.


All of the above.

If the second argument to setlocale(3) is 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 \(aq\\0\(aq. */
  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;  



The GNU gettext functions are specified in LI18NUX2000.


locale(1), localedef(1), gettext(3), localeconv(3), ngettext(3), nl_langinfo(3), rpmatch(3), setlocale(3), strcoll(3), strfmon(3), strftime(3), strxfrm(3)


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  Copyright (c) 1993 by Thomas Koenig (

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Modified Sat Jul 24 17:28:34 1993 by Rik Faith <>
Modified Sun Jun 01 17:16:34 1997 by Jochen Hein
Modified Thu Apr 25 00:43:19 2002 by Bruno Haible <>