setlocale(3p) — Linux manual page


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

PROLOG         top

       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         top

       setlocale — set program locale

SYNOPSIS         top

       #include <locale.h>

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

DESCRIPTION         top

       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

       LC_MONETARY Affects the behavior of functions that handle
                   monetary values.

       LC_NUMERIC  Affects the behavior of functions that handle numeric

       LC_TIME     Affects the behavior of the time conversion

       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         top

       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

       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         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top



       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

           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

           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         top

       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,

        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,


       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

               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(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

             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



SEE ALSO         top

       catopen(3p), exec(1p), fprintf(3p), fscanf(3p), isalnum(3p),
       isalpha(3p), isblank(3p), iscntrl(3p), isdigit(3p), isgraph(3p),
       islower(3p), isprint(3p), ispunct(3p), isspace(3p), isupper(3p),
       iswalnum(3p), iswalpha(3p), iswblank(3p), iswcntrl(3p),
       iswctype(3p), iswdigit(3p), iswgraph(3p), iswlower(3p),
       iswprint(3p), iswpunct(3p), iswspace(3p), iswupper(3p),
       iswxdigit(3p), isxdigit(3p), localeconv(3p), mblen(3p),
       mbstowcs(3p), mbtowc(3p), newlocale(3p), nl_langinfo(3p),
       perror(3p), psiginfo(3p), strcoll(3p), strerror(3p), strfmon(3p),
       strsignal(3p), strtod(3p), strxfrm(3p), tolower(3p), toupper(3p),
       towlower(3p), towupper(3p), uselocale(3p), wcscoll(3p),
       wcstod(3p), wcstombs(3p), wcsxfrm(3p), wctomb(3p)

       The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale,
       Chapter 8, Environment Variables, langinfo.h(0p), locale.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                     SETLOCALE(3P)

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