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Manual Pages  — SETLOCALE


setlocale – natural language formatting for C



Standard C Library (libc, -lc)


#include <locale.h>

char *
setlocale(int category, const char *locale);


The setlocale() function sets the C library's notion of natural language formatting style for particular sets of routines. Each such style is called a 'locale' and is invoked using an appropriate name passed as a C string.

The setlocale() function recognizes several categories of routines. These are the categories and the sets of routines they select:
LC_ALL Set the entire locale generically.
LC_COLLATE Set a locale for string collation routines. This controls alphabetic ordering in strcoll() and strxfrm().
LC_CTYPE Set a locale for the ctype(3) and multibyte(3) functions. This controls recognition of upper and lower case, alphabetic or non-alphabetic characters, and so on.
  Set a locale for message catalogs, see catopen(3) function.
  Set a locale for formatting monetary values; this affects the localeconv() function.
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 printf() and scanf(), as well as values returned by localeconv().
LC_TIME Set a locale for formatting dates and times using the strftime() function.
LANG Sets the generic locale category for native language, local customs and coded character set in the absence of more specific locale variables.

Only three locales are defined by default, the empty string amp;"" which denotes the native environment, and the amp;"C" and amp;"POSIX" locales, which denote the C language environment. A locale argument of NULL causes setlocale() to return the current locale.

The option -a to the locale(1) command can be used to display all further possible names for the locale argument that are recognized. Specifying any unrecognized value for locale makes setlocale() fail.

By default, C programs start in the amp;"C" locale.

The only function in the library that sets the locale is setlocale(); the locale is never changed as a side effect of some other routine.


Upon successful completion, setlocale() returns the string associated with the specified category for the requested locale. The setlocale() function returns NULL and fails to change the locale if the given combination of category and locale makes no sense.


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:
    setlocale(LC_ALL, "de");
    setlocale(LC_COLLATE, "fr");

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:

    setlocale(LC_ALL, "");


$PATH_LOCALE/ locale/category
/usr/share/locale/ locale/category
  locale file for the locale locale and the category category.


No errors are defined.


locale(1), localedef(1), catopen(3), ctype(3), localeconv(3), multibyte(3), strcoll(3), strxfrm(3), euc(5), utf8(5), environ(7)


The setlocale() function conforms to ISO/IEC 9899:1999 ("ISO C99").


The setlocale() function first appeared in BSD 4.4 .

SETLOCALE (3) August 7, 2020

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