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This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
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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 .