libc/locale/setlocale.3

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.Dd August 7, 2020
.Dt SETLOCALE 3
.Os
.Sh NAME
.Nm setlocale
.Nd natural language formatting for C
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In locale.h
.Ft char *
.Fn setlocale "int category" "const char *locale"
.Sh DESCRIPTION
The
.Fn setlocale
function sets the C library's notion
of natural language formatting style
for particular sets of routines.
Each such style is called a
.Sq locale
and is invoked using an appropriate name passed as a C string.
.Pp
The
.Fn setlocale
function recognizes several categories of routines.
These are the categories and the sets of routines they select:
.Bl -tag -width LC_MONETARY
.It Dv LC_ALL
Set the entire locale generically.
.It Dv LC_COLLATE
Set a locale for string collation routines.
This controls alphabetic ordering in
.Fn strcoll
and
.Fn strxfrm .
.It Dv LC_CTYPE
Set a locale for the
.Xr ctype 3
and
.Xr multibyte 3
functions.
This controls recognition of upper and lower case,
alphabetic or non-alphabetic characters,
and so on.
.It Dv LC_MESSAGES
Set a locale for message catalogs, see
.Xr catopen 3
function.
.It Dv LC_MONETARY
Set a locale for formatting monetary values;
this affects the
.Fn localeconv
function.
.It Dv LC_NUMERIC
Set a locale for formatting numbers.
This controls the formatting of decimal points
in input and output of floating point numbers
in functions such as
.Fn printf
and
.Fn scanf ,
as well as values returned by
.Fn localeconv .
.It Dv LC_TIME
Set a locale for formatting dates and times using the
.Fn strftime
function.
.It Dv LANG
Sets the generic locale category for native language, local customs
and coded character set in the absence of more specific locale
variables.
.El
.Pp
Only three locales are defined by default,
the empty string
.Li \&"\|"
which denotes the native environment, and the
.Li \&"C"
and
.Li \&"POSIX"
locales, which denote the C language environment.
A
.Fa locale
argument of
.Dv NULL
causes
.Fn setlocale
to return the current locale.
.Pp
The option
.Fl a
to the
.Xr locale 1
command can be used to display all further possible names for the
.Fa locale
argument that are recognized.
Specifying any unrecognized value for
.Fa locale
makes
.Fn setlocale
fail.
.Pp
By default, C programs start in the
.Li \&"C"
locale.
.Pp
The only function in the library that sets the locale is
.Fn setlocale ;
the locale is never changed as a side effect of some other routine.
.Sh RETURN VALUES
Upon successful completion,
.Fn setlocale
returns the string associated with the specified
.Fa category
for the requested
.Fa locale .
The
.Fn setlocale
function returns
.Dv NULL
and fails to change the locale
if the given combination of
.Fa category
and
.Fa locale
makes no sense.
.Sh FILES
.Bl -tag -width /usr/share/locale/locale/category -compact
.It Pa $PATH_LOCALE/ Ns Em locale/category
.It Pa /usr/share/locale/ Ns Em locale/category
locale file for the locale
.Em locale
and the category
.Em category .
.El
.Sh EXAMPLES
The following code illustrates how a program can initialize the
international environment for one language, while selectively
modifying the program's locale such that regular expressions and
string operations can be applied to text recorded in a different
language:
.Bd -literal
    setlocale(LC_ALL, "de");
    setlocale(LC_COLLATE, "fr");
.Ed
.Pp
When a process is started, its current locale is set to the C or POSIX
locale.
An internationalized program that depends on locale data not defined in
the C or POSIX locale must invoke the setlocale subroutine in the
following manner before using any of the locale-specific information:
.Bd -literal
    setlocale(LC_ALL, "");
.Ed
.Sh ERRORS
No errors are defined.
.Sh SEE ALSO
.Xr locale 1 ,
.Xr localedef 1 ,
.Xr catopen 3 ,
.Xr ctype 3 ,
.Xr localeconv 3 ,
.Xr multibyte 3 ,
.Xr strcoll 3 ,
.Xr strxfrm 3 ,
.Xr euc 5 ,
.Xr utf8 5 ,
.Xr environ 7
.Sh STANDARDS
The
.Fn setlocale
function conforms to
.St -isoC-99 .
.Sh HISTORY
The
.Fn setlocale
function first appeared in
.Bx 4.4 .