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.\" @(#)setlocale.3 8.1 (Berkeley) 6/9/93
.Dd August 7, 2020
.Dt SETLOCALE 3
.Nd natural language formatting for C
.Ft char *
.Fn setlocale "int category" "const char *locale"
function sets the C library's notion
of natural language formatting style
for particular sets of routines.
Each such style is called a
and is invoked using an appropriate name passed as a C string.
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 strxfrm .
.It Dv LC_CTYPE
Set a locale for the
.Xr ctype 3
.Xr multibyte 3
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
.It Dv LC_MONETARY
Set a locale for formatting monetary values;
this affects the
.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 scanf ,
as well as values returned by
.Fn localeconv .
.It Dv LC_TIME
Set a locale for formatting dates and times using the
.It Dv LANG
Sets the generic locale category for native language, local customs
and coded character set in the absence of more specific locale
Only three locales are defined by default,
the empty string
which denotes the native environment, and the
locales, which denote the C language environment.
to return the current locale.
.Xr locale 1
command can be used to display all further possible names for the
argument that are recognized.
Specifying any unrecognized value for
By default, C programs start in the
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,
returns the string associated with the specified
for the requested
.Fa locale .
and fails to change the locale
if the given combination of
makes no sense.
.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
and the category
.Em category .
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
When a process is started, its current locale is set to the C or POSIX
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:
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
function conforms to
.St -isoC-99 .
function first appeared in
.Bx 4.4 .