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

       The array pointed to by the return value should not be modified by the program, but may  be  modified  by
       further calls to these functions.

       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                                   NL_LANGINFO(3POSIX)

       The nl_langinfo() and nl_langinfo_l() functions shall return a pointer to a string containing information
       relevant  to  the  particular  language  or cultural area defined in the current locale, or in the locale
       represented by locale, respectively (see <langinfo.h>).  The manifest constant names and values  of  item
       are defined in <langinfo.h>.  For example:

           nl_langinfo(ABDAY_1)

       would  return  a  pointer to the string "Dom" if the identified language was Portuguese, and "Sun" if the
       identified language was English.

           nl_langinfo_l(ABDAY_1, loc)

       would return a pointer to the string "Dom" if the identified language of the locale  represented  by  loc
       was Portuguese, and "Sun" if the identified language of the locale represented by loc was English.

       The nl_langinfo() function need not be thread-safe.

       The  behavior  is  undefined  if  the  locale  argument  to  nl_langinfo_l() is the special locale object
       LC_GLOBAL_LOCALE or is not a valid locale object handle.

       No errors are defined.

       Thefollowingsectionsareinformative.

GettingDateandTimeFormattingInformation
       The  following  example returns a pointer to a string containing date and time formatting information, as
       defined in the LC_TIME category of the current locale.

           #include <time.h>
           #include <langinfo.h>
           ...
           strftime(datestring, sizeof(datestring), nl_langinfo(D_T_FMT), tm);
           ...

       None.

       nl_langinfo, nl_langinfo_l — language information

       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.

       The possible interactions between internal data used by nl_langinfo() and nl_langinfo_l() are complicated
       by  the  fact  that  nl_langinfo_l()  must  be  thread-safe  but  nl_langinfo()  need not be. The various
       implementation choices are:

        1. nl_langinfo_l() and nl_langinfo() use separate buffers, or at least one  of  them  does  not  use  an
           internal string buffer. In this case there are no interactions.

        2. nl_langinfo_l() and nl_langinfo() share an internal per-thread buffer. There can be interactions, but
           only in the same thread.

        3. nl_langinfo_l()  uses an internal per-thread buffer, and nl_langinfo() uses (in all threads) the same
           buffer that nl_langinfo_l() uses in the initial thread. There can  be  interactions,  but  only  when
           nl_langinfo_l() is called in the initial thread.

       In a locale where langinfo  data  is  not  defined,  these  functions  shall  return  a  pointer  to  the
       corresponding  string  in  the POSIX locale. In all locales, these functions shall return a pointer to an
       empty string if item contains an invalid setting.

       The application shall not modify the string returned. The pointer  returned  by  nl_langinfo()  might  be
       invalidated  or  the  string  content  might  be overwritten by a subsequent call to nl_langinfo() in any
       thread or to nl_langinfo_l() in the same thread or the initial thread, by subsequent calls to setlocale()
       with a category corresponding to the category of item (see <langinfo.h>) or the category  LC_ALL,  or  by
       subsequent  calls  to  uselocale()  which change the category corresponding to the category of item.  The
       pointer returned by nl_langinfo_l() might be invalidated or the string content might be overwritten by  a
       subsequent call to nl_langinfo_l() in the same thread or to nl_langinfo() in any thread, or by subsequent
       calls  to  freelocale()  or  newlocale()  which  free  or  modify  the  locale  object that was passed to
       nl_langinfo_l().  The returned pointer and the string content might also be invalidated  if  the  calling
       thread is terminated.

setlocale(), uselocale()

       The Base Definitions volume of POSIX.1‐2017, Chapter7, Locale, <langinfo.h>, <locale.h>, <nl_types.h>

       #include <langinfo.h>

       char *nl_langinfo(nl_item item);
       char *nl_langinfo_l(nl_item item, locale_t locale);