1  /* Provide tzset for systems that don't have it or for which it's broken.
       2  
       3     Copyright (C) 2001-2003, 2005-2007, 2009-2023 Free Software Foundation, Inc.
       4  
       5     This file is free software: you can redistribute it and/or modify
       6     it under the terms of the GNU Lesser General Public License as
       7     published by the Free Software Foundation, either version 3 of the
       8     License, or (at your option) any later version.
       9  
      10     This file is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      13     GNU Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public License
      16     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      17  
      18  /* written by Jim Meyering */
      19  
      20  #include <config.h>
      21  
      22  /* Specification.  */
      23  #include <time.h>
      24  
      25  #include <stdlib.h>
      26  #include <string.h>
      27  
      28  void
      29  rpl_tzset (void)
      30  #undef tzset
      31  {
      32  #if defined _WIN32 && ! defined __CYGWIN__
      33    /* Rectify the value of the environment variable TZ.
      34       There are four possible kinds of such values:
      35         - Traditional US time zone names, e.g. "PST8PDT".  Syntax: see
      36           <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset>
      37         - Time zone names based on geography, that contain one or more
      38           slashes, e.g. "Europe/Moscow".
      39         - Time zone names based on geography, without slashes, e.g.
      40           "Singapore".
      41         - Time zone names that contain explicit DST rules.  Syntax: see
      42           <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03>
      43       The Microsoft CRT understands only the first kind.  It produces incorrect
      44       results if the value of TZ is of the other kinds.
      45       But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value
      46       of the second kind for most geographies, or of the first kind in a few
      47       other geographies.  If it is of the second kind, neutralize it.  For the
      48       Microsoft CRT, an absent or empty TZ means the time zone that the user
      49       has set in the Windows Control Panel.
      50       If the value of TZ is of the third or fourth kind -- Cygwin programs
      51       understand these syntaxes as well --, it does not matter whether we
      52       neutralize it or not, since these values occur only when a Cygwin user
      53       has set TZ explicitly; this case is 1. rare and 2. under the user's
      54       responsibility.  */
      55    const char *tz = getenv ("TZ");
      56    if (tz != NULL && strchr (tz, '/') != NULL)
      57      _putenv ("TZ=");
      58  
      59    /* On native Windows, tzset() is deprecated.  Use _tzset() instead.  See
      60       <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/posix-tzset>
      61       <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset>  */
      62    _tzset ();
      63  #else
      64    tzset ();
      65  #endif
      66  }