1  /* Work around platform bugs in localtime.
       2     Copyright (C) 2017-2023 Free Software Foundation, Inc.
       3  
       4     This file is free software: you can redistribute it and/or modify
       5     it under the terms of the GNU Lesser General Public License as
       6     published by the Free Software Foundation; either version 2.1 of the
       7     License, or (at your option) any later version.
       8  
       9     This file is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      12     GNU Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public License
      15     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      16  
      17  #include <config.h>
      18  
      19  /* Specification.  */
      20  #include <time.h>
      21  
      22  #include <stdlib.h>
      23  #include <string.h>
      24  
      25  #undef localtime
      26  
      27  struct tm *
      28  rpl_localtime (const time_t *tp)
      29  {
      30  #if defined _WIN32 && ! defined __CYGWIN__
      31    /* Rectify the value of the environment variable TZ.
      32       There are four possible kinds of such values:
      33         - Traditional US time zone names, e.g. "PST8PDT".  Syntax: see
      34           <https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset>
      35         - Time zone names based on geography, that contain one or more
      36           slashes, e.g. "Europe/Moscow".
      37         - Time zone names based on geography, without slashes, e.g.
      38           "Singapore".
      39         - Time zone names that contain explicit DST rules.  Syntax: see
      40           <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03>
      41       The Microsoft CRT understands only the first kind.  It produces incorrect
      42       results if the value of TZ is of the other kinds.
      43       But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value
      44       of the second kind for most geographies, or of the first kind in a few
      45       other geographies.  If it is of the second kind, neutralize it.  For the
      46       Microsoft CRT, an absent or empty TZ means the time zone that the user
      47       has set in the Windows Control Panel.
      48       If the value of TZ is of the third or fourth kind -- Cygwin programs
      49       understand these syntaxes as well --, it does not matter whether we
      50       neutralize it or not, since these values occur only when a Cygwin user
      51       has set TZ explicitly; this case is 1. rare and 2. under the user's
      52       responsibility.  */
      53    const char *tz = getenv ("TZ");
      54    if (tz != NULL && strchr (tz, '/') != NULL)
      55      _putenv ("TZ=");
      56  #endif
      57  
      58    return localtime (tp);
      59  }