Re: gettimeofday does noet return UTC offset

[Scott Klement <klemscot@xxxxxxxxxxxx>]

On Wed, 29 Oct 2003, James Rich wrote:
>
> Notice "on some architectures".  Most likely is that the timezone
> structure is not filled out on the iSeries platform.  If so, this is not
> a bug.

Do you know for a fact that this is the reason, or is it just a guess?
When I look in the iSeries Information Center, I see this:

  tzp
    (Output) A pointer to a timezone structure that contains the local
    time zone (measured in minutes of time westward from Greenwich) and
    a flag that, if nonzero, indicates daylight saving time applies locally
    during the appropriate part of the year.

It says NOTHING about the time zone not being filled in, despite that this
is an iSeries-specific manual.   In fact, there's an example at the end of
this page which shows output like this:

   Example Output:
   gettimeofday() successful.
   time = 866208142.290944, minuteswest = 360, dsttime = 1

Why would IBM put an example in their own iSeries manual that shows the
timezone being returned if they don't support it?

Something isn't right here.  Either their documentation is really really
misleading, or something else is wrong, here..


> It isn't filled out on linux either (and I don't think it is on
> *BSD).

Correct, it's not used in FreeBSD (I don't know about the other BSDs) but
the manual page for FreeBSD clearly tells you that.

> gettimeofday() is designed to tell what time the software clock
> thinks it is, not necessarily what timezone you are in.  The time value
> in struct *tv is already adjusted for your timezone.

No, it's not.  The time returned by gettimeofday() is the seconds from Jan
1 1970, UTC, NOT the local time.  This is documented in the Infocenter as
well, but I also tested it with a quick program...

Here's my test program, I deliberately coded this so that it would work
on V4R2 or later (since that's when the API was introduced).  On my
system, it returns the UTC time and 0 for the minutes west.

     H DFTACTGRP(*NO) BNDDIR('QC2LE')

     D tv              ds
     D   tv_sec                      10U 0
     D   tv_usec                     10I 0

     D tz              ds
     D   tz_minwest                  10I 0
     D   tz_dstttime                 10I 0

     D gettimeofday    PR            10I 0 ExtProc('gettimeofday')
     D   tp                            *   value
     D   tzp                           *   value

     D ts              s               Z
     D msg             s             52A
     D showts          s             26a
     D rc              s             10I 0

     c                   eval      rc = gettimeofday(%addr(tv): %addr(tz))

     c                   if        rc < 0
     c                   eval      Msg = 'gettimeofday() failed.'
     c                   dsply                   Msg

     c                   else
     c                   eval      ts = z'1970-01-01-00.00.00'
     c                   adddur    tv_sec:*S     ts
     c                   eval      Msg = 'You are ' + %char(tz_minwest) +
     c                              ' minutes west of UTC'
     c                   dsply                   msg
     c                   move      ts            showts
     c                   eval      Msg = 'it is ' + showts
     c                   dsply                   msg
     c                   endif

     c                   eval      *inlr = *on