SETLOCALE(3)               POSIX Programmer's Manual              SETLOCALE(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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(3)
