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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
NAME
setlocale — set program locale
SYNOPSIS
#include <locale.h>
char *setlocale(int category, const char *locale);
DESCRIPTION
The functionality described on this reference page is aligned with the ISO C standard. Any conflict
between the requirements described here and the ISO C standard is unintentional. This volume of
POSIX.1‐2017 defers to the ISO C standard.
The setlocale() function selects the appropriate piece of the global locale, as specified by the category
and locale arguments, and can be used to change or query the entire global locale or portions thereof.
The value LC_ALL for category names the entire global locale; other values for category name only a part
of the global locale:
LC_COLLATE Affects the behavior of regular expressions and the collation functions.
LC_CTYPE Affects the behavior of regular expressions, character classification, character conversion
functions, and wide-character functions.
LC_MESSAGES Affects the affirmative and negative response expressions returned by nl_langinfo() and the
way message catalogs are located. It may also affect the behavior of functions that return or
write message strings.
LC_MONETARY Affects the behavior of functions that handle monetary values.
LC_NUMERIC Affects the behavior of functions that handle numeric values.
LC_TIME Affects the behavior of the time conversion functions.
The locale argument is a pointer to a character string containing the required setting of category. The
contents of this string are implementation-defined. In addition, the following preset values of locale
are defined for all settings of category:
"POSIX" Specifies the minimal environment for C-language translation called the POSIX locale. The
POSIX locale is the default global locale at entry to main().
"C" Equivalent to "POSIX".
"" Specifies an implementation-defined native environment. The determination of the name of the
new locale for the specified category depends on the value of the associated environment
variables, LC_* and LANG; see the Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale
and Chapter 8, Environment Variables.
A null pointer
Directs setlocale() to query the current global locale setting and return the name of the
locale if category is not LC_ALL, or a string which encodes the locale name(s) for all of the
individual categories if category is LC_ALL.
Setting all of the categories of the global locale is similar to successively setting each individual
category of the global locale, except that all error checking is done before any actions are performed.
To set all the categories of the global locale, setlocale() can be invoked as:
setlocale(LC_ALL, "");
In this case, setlocale() shall first verify that the values of all the environment variables it needs
according to the precedence rules (described in the Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables) indicate supported locales. If the value of any of these environment variable
searches yields a locale that is not supported (and non-null), setlocale() shall return a null pointer
and the global locale shall not be changed. If all environment variables name supported locales,
setlocale() shall proceed as if it had been called for each category, using the appropriate value from
the associated environment variable or from the implementation-defined default if there is no such value.
The global locale established using setlocale() shall only be used in threads for which no current locale
has been set using uselocale() or whose current locale has been set to the global locale using
uselocale(LC_GLOBAL_LOCALE).
The implementation shall behave as if no function defined in this volume of POSIX.1‐2017 calls
setlocale().
The setlocale() function need not be thread-safe.
RETURN VALUE
Upon successful completion, setlocale() shall return the string associated with the specified category
for the new locale. Otherwise, setlocale() shall return a null pointer and the global locale shall not be
changed.
A null pointer for locale shall cause setlocale() to return a pointer to the string associated with the
specified category for the current global locale. The global locale shall not be changed.
The string returned by setlocale() is such that a subsequent call with that string and its associated
category shall restore that part of the global locale. The application shall not modify the string
returned. The returned string pointer might be invalidated or the string content might be overwritten by
a subsequent call to setlocale(). The returned pointer might also be invalidated if the calling thread
is terminated.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The following code illustrates how a program can initialize the international environment for one
language, while selectively modifying the global 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@dict");
Internationalized programs can initiate language operation according to environment variable settings
(see the Base Definitions volume of POSIX.1‐2017, Section 8.2, Internationalization Variables) by calling
setlocale() as follows:
setlocale(LC_ALL, "");
Changing the setting of LC_MESSAGES has no effect on catalogs that have already been opened by calls to
catopen().
In order to make use of different locale settings while multiple threads are running, applications should
use uselocale() in preference to setlocale().
RATIONALE
References to the international environment or locale in the following text relate to the global locale
for the process. This can be overridden for individual threads using uselocale().
The ISO C standard defines a collection of functions to support internationalization. One of the most
significant aspects of these functions is a facility to set and query the international environment. The
international environment is a repository of information that affects the behavior of certain
functionality, namely:
1. Character handling
2. Collating
3. Date/time formatting
4. Numeric editing
5. Monetary formatting
6. Messaging
The setlocale() function provides the application developer with the ability to set all or portions,
called categories, of the international environment. These categories correspond to the areas of
functionality mentioned above. The syntax for setlocale() is as follows:
char *setlocale(int category, const char *locale);
where category is the name of one of following categories, namely:
LC_COLLATE LC_CTYPE LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME
In addition, a special value called LC_ALL directs setlocale() to set all categories.
There are two primary uses of setlocale():
1. Querying the international environment to find out what it is set to
2. Setting the international environment, or locale, to a specific value
The behavior of setlocale() in these two areas is described below. Since it is difficult to describe the
behavior in words, examples are used to illustrate the behavior of specific uses.
To query the international environment, setlocale() is invoked with a specific category and the null
pointer as the locale. The null pointer is a special directive to setlocale() that tells it to query
rather than set the international environment. The following syntax is used to query the name of the
international environment:
setlocale({LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY, \
LC_NUMERIC, LC_TIME},(char *) NULL);
The setlocale() function shall return the string corresponding to the current international environment.
This value may be used by a subsequent call to setlocale() to reset the international environment to this
value. However, it should be noted that the return value from setlocale() may be a pointer to a static
area within the function and is not guaranteed to remain unchanged (that is, it may be modified by a
subsequent call to setlocale()). Therefore, if the purpose of calling setlocale() is to save the value
of the current international environment so it can be changed and reset later, the return value should be
copied to an array of char in the calling program.
There are three ways to set the international environment with setlocale():
setlocale(category, string)
This usage sets a specific category in the international environment to a specific value
corresponding to the value of the string. A specific example is provided below:
setlocale(LC_ALL, "fr_FR.ISO-8859-1");
In this example, all categories of the international environment are set to the locale
corresponding to the string "fr_FR.ISO-8859-1", or to the French language as spoken in France using
the ISO/IEC 8859‐1:1998 standard codeset.
If the string does not correspond to a valid locale, setlocale() shall return a null pointer and
the international environment is not changed. Otherwise, setlocale() shall return the name of the
locale just set.
setlocale(category, "C")
The ISO C standard states that one locale must exist on all conforming implementations. The name of
the locale is C and corresponds to a minimal international environment needed to support the C
programming language.
setlocale(category, "")
This sets a specific category to an implementation-defined default. This corresponds to the value
of the environment variables.
FUTURE DIRECTIONS
None.
SEE ALSO
catopen(), exec, fprintf(), fscanf(), isalnum(), isalpha(), isblank(), iscntrl(), isdigit(), isgraph(),
islower(), isprint(), ispunct(), isspace(), isupper(), iswalnum(), iswalpha(), iswblank(), iswcntrl(),
iswctype(), iswdigit(), iswgraph(), iswlower(), iswprint(), iswpunct(), iswspace(), iswupper(),
iswxdigit(), isxdigit(), localeconv(), mblen(), mbstowcs(), mbtowc(), newlocale(), nl_langinfo(),
perror(), psiginfo(), strcoll(), strerror(), strfmon(), strsignal(), strtod(), strxfrm(), tolower(),
toupper(), towlower(), towupper(), uselocale(), wcscoll(), wcstod(), wcstombs(), wcsxfrm(), wctomb()
The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale, Chapter 8, Environment Variables,
<langinfo.h>, <locale.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 SETLOCALE(3POSIX)