lib/ctime.c

   1 /* Work around platform bugs in ctime.
   2    Copyright (C) 2017-2020 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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 General Public License for more details.
  13
  14    You should have received a copy of the GNU 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 ctime
  26
  27 char *
  28 rpl_ctime (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 ctime (tp);
  59 }