lib/tzset.c

   1 /* Provide tzset for systems that don't have it or for which it's broken.
   2
   3    Copyright (C) 2001-2003, 2005-2007, 2009-2020 Free Software Foundation, Inc.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program 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 General Public License for more details.
  14
  15    You should have received a copy of the GNU 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 }