[tz] Java & Rearguard

Russ Allbery eagle at eyrie.org
Thu Jun 6 19:22:22 UTC 2019

scs at eskimo.com (Steve Summit) writes:

> (As an aside: Is it my imagination, or was there a time when C had an
> array of 1, 2, or maybe more than 2 time zone strings, and you used
> tm_isdst as an index into them, such that tm_isdst functioned as a sort
> of an opaque token even though it had "dst" in its name?)

tzname, and it's still a supported API (documented in tzset(3) on Linux).
INN uses it when generating Date headers if it's available and tm.tm_zone
is not (in a bit of portability that is now probably only applicable to
museum exhibitions):

    /* Now, get a pointer to the time zone abbreviation, and if there is
       enough room in the buffer, add it to the end of the date string as a
       comment. */
    if (!local) {
        tz_name = "UTC";
    } else {
        tz_name = tm.tm_zone;
        tz_name = tzname[(tm.tm_isdst > 0) ? 1 : 0];
        tz_name = NULL;


    The tzset() function initializes the tzname variable from the TZ
    environment variable.  This function is automatically called by the
    other time conversion functions that depend on the timezone.  In a
    System-V-like environment, it will also set the variables timezone
    (seconds West of UTC) and daylight (to 0 if this timezone does not
    have any daylight saving time rules, or to nonzero if there is a time,
    past, present or future when daylight saving time applies).

Russ Allbery (eagle at eyrie.org)              <http://www.eyrie.org/~eagle/>

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