diff options
Diffstat (limited to 'lib/mktime.c')
| -rw-r--r-- | lib/mktime.c | 25 |
1 files changed, 22 insertions, 3 deletions
diff --git a/lib/mktime.c b/lib/mktime.c index a78d960e53..72df770c1a 100644 --- a/lib/mktime.c +++ b/lib/mktime.c @@ -491,9 +491,28 @@ time_t mktime (struct tm *tp) { # if NEED_MKTIME_WINDOWS - /* If the environment variable TZ has been set by Cygwin, neutralize it. - The Microsoft CRT interprets TZ differently than Cygwin and produces - incorrect results if TZ has the syntax used by Cygwin. */ + /* Rectify the value of the environment variable TZ. + There are four possible kinds of such values: + - Traditional US time zone names, e.g. "PST8PDT". Syntax: see + <https://msdn.microsoft.com/en-us/library/90s5c885.aspx> + - Time zone names based on geography, that contain one or more + slashes, e.g. "Europe/Moscow". + - Time zone names based on geography, without slashes, e.g. + "Singapore". + - Time zone names that contain explicit DST rules. Syntax: see + <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03> + The Microsoft CRT understands only the first kind. It produces incorrect + results if the value of TZ is of the other kinds. + But in a Cygwin environment, /etc/profile.d/tzset.sh sets TZ to a value + of the second kind for most geographies, or of the first kind in a few + other geographies. If it is of the second kind, neutralize it. For the + Microsoft CRT, an absent or empty TZ means the time zone that the user + has set in the Windows Control Panel. + If the value of TZ is of the third or fourth kind -- Cygwin programs + understand these syntaxes as well --, it does not matter whether we + neutralize it or not, since these values occur only when a Cygwin user + has set TZ explicitly; this case is 1. rare and 2. under the user's + responsibility. */ const char *tz = getenv ("TZ"); if (tz != NULL && strchr (tz, '/') != NULL) _putenv ("TZ="); |