man-pages/man7/locale.7

.\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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.\" Modified Sat Jul 24 17:28:34 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Sun Jun 01 17:16:34 1997 by Jochen Hein
.\"   <jochen.hein@delphi.central.de>
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.\"
.TH LOCALE 7  1993-04-24 "Linux" "Linux Programmer's Manual"
.SH NAME
locale \- Description of multi-language support
.SH SYNOPSIS
.nf
.B #include <locale.h>
.fi
.SH DESCRIPTION
A locale is a set of language and cultural rules.  These cover aspects
such as language for messages, different character sets, lexicographic
conventions, etc.  A program needs to be able to determine its locale
and act accordingly to be portable to different cultures.
.PP
The header
.I <locale.h>
declares data types, functions and macros which are useful in this
task.
.PP
The functions it declares are
.BR setlocale ()
to set the current locale, and
.BR localeconv ()
to get information about number formatting.
.PP
There are different categories for local information a program might
need; they are declared as macros.  Using them as the first argument
to the
.BR setlocale ()
function, it is possible to set one of these to the desired locale:
.TP
.B LC_COLLATE
This is used to change the behaviour of the functions
.BR strcoll ()
and
.BR strxfrm (),
which are used to compare strings in the local alphabet.  For example,
the German sharp s is sorted as "ss".
.TP
.B LC_CTYPE
This changes the behaviour of the character handling and
classification functions, such as
.BR isupper ()
and
.BR toupper (),
and the multi\-byte character functions such as
.BR mblen ()
or
.BR wctomb ().
.TP
.B LC_MONETARY
changes the information returned by
.BR localeconv ()
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
.BR strfmon ().
.TP
.B LC_MESSAGES
changes the language messages are displayed in and how an affirmative or
negative answer looks like.  The GNU C-library contains the
.BR gettext (),
.BR ngettext (),
and
.BR rpmatch ()
functions to ease the use of these information.  The GNU gettext family of
functions also obey the environment variable
.BR LANGUAGE .
.TP
.B LC_NUMERIC
changes the information used by the
.BR printf ()
and
.BR scanf ()
family of functions, when they are advised to use the
locale-settings.  This information can also be read with the 
.BR localeconv ()
function.
.TP
.B LC_TIME
changes the behaviour of the
.BR strftime ()
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.
.TP
.B LC_ALL
All of the above.
.\" FIXME glibc 2.2.2 added new non-standard locale categories:
.\" LC_ADDRESS, LC_IDENTIFICATION, LC_MEASUREMENT, LC_NAME,
.\" LC_PAPER, LC_TELEPHONE.  These need to be documented.
.PP
If the second argument to
.BR setlocale ()
is empty string,
.BR """""" ,
for the default locale, it is determined using the following steps:
.IP 1.
If there is a non-null environment variable
.BR LC_ALL ,
the value of
.B LC_ALL
is used.
.IP 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.
.IP 3.
If there is a non-null environment variable
.BR LANG ,
the value of
.B LANG
is used.
.PP
Values about local numeric formatting is made available in a
.I struct lconv
returned by the
.BR localeconv ()
function, which has the following declaration:
.in +0.25i
.nf

struct lconv {

  /* Numeric (non-monetary) 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;   /* Int'l 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;
};
.fi
.in +0.25i
.SH "CONFORMING TO"
POSIX.1-2001.

The GNU gettext functions are specified in LI18NUX2000.
.SH "SEE ALSO"
.BR locale (1),
.BR localedef (1),
.BR gettext (3),
.BR localeconv (3),
.BR ngettext (3),
.BR nl_langinfo (3),
.BR rpmatch (3),
.BR setlocale (3),
.BR strcoll (3),
.BR strfmon (3),
.BR strftime (3),
.BR strxfrm (3)