From owner-freebsd-stable  Thu Oct 17 21:21:37 2002
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 freebsd-stable@freebsd.org; Thu, 17 Oct 2002 21:21:34 -0700 (PDT)
Date: Thu, 17 Oct 2002 21:21:34 -0700 (PDT)
From: =?ISO-8859-1?Q?Mikko_Ty=F6l=E4j=E4rvi?= <mbsd@pacbell.net>
Subject: Re: mktime problem?
In-reply-to: <3DAF7D3A.7060603@ntmk.ru>
X-X-Sender: mikko@atlas.home
To: Boris Kovalenko <boris@ntmk.ru>
Cc: freebsd-stable@freebsd.org
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On Fri, 18 Oct 2002, Boris Kovalenko wrote:

> Hello!
>
> First the simple source code:
> #include <stdio.h>
> #include <sys/time.h>
>
> int main(int argc, char **argv)
> {
>     time_t      today = time( NULL );
>     struct tm   temp  = *localtime( &today );
>
>     temp.tm_hour = 24;
>     temp.tm_min  = 0;
>     temp.tm_sec  = 0;
>     temp.tm_mday = 27;

      printf("is dst = %d\n", temp.tm_isdst);
      temp.tm_isdst = -1;

>
>     today = mktime( &temp );
>     printf("%s\n", ctime( &today ));
>     return 0;
> }
>
> I expect 28 Oct 00:00, but got 27 Oct 23:00. Why? Daylight saving should
> be at 28 Oct 02:00? My zoneinfo is Yekaterinburg.

Seems to be intentional:

% man mktime
[...]

"A positive or zero value for tm_isdst causes mktime() to presume
 initially that summer time (for example, Daylight Saving Time) is or
 is not in effect for the specified time, respectively.  A negative
 value for tm_isdst causes the mktime() function to attempt to divine
 whether summer time is in effect for the specified time."

Looks like a verbatim copy of the text in IEEE Std 1003.1-2001 (SUSv3).

  $.02,
  /Mikko


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