Conference turris::digital_unix

9360.0. "Epoch & mktime daylight savings" by NETRIX::"[email protected]" (Richard Quan) Wed Apr 02 1997 09:28

Melbourne University have a problem with their PMDF application which Innosoft
have tracked
down to be a problem with establishing the epoch. I am able to repeat the
problem on my
machine running 4.0A. A summary of the problem is:
A. Epoch is 00:00:00 Jan 1 1970 GMT or GMT + 10 AEST (Australian Eastern
Standard Time)
B. Calling the re-entrant version of ctime with 0 seconds confirms the above
epoch adjusted 
   for the local time zone.
C. Calling mktime with the current local time set (to 10) with no daylight
savings returns a correct 
   value of 0 secs. With the daylight savings set to 1 a value of -3600 is 
   returned; ie 1 hour before the epoch.

Is this because 4.0A assumes that there is a 11 hour difference when daylight
savings is in effect;
ie GMT + 10 + 1. Thus for 10 hours past the epoch this would equate to the
epoch - 1hour (-3600) + 11.

Does anyone know if this behaviour is consistent in previous versions of DU;
ie 3.x?

=====
Richard.
   Here is the problem that PMDF is complaining about (again running on
DUNIX 4.0A, and from memory 4.0B). Dunix does not seem to know what the
epoch is even though you can test it with a 0 buffer. Sample code supplied
by Innosoft.

The tm_isdst variable is important. You can get the program to return the
correct value for the epoch by setting the tm_isdst variable to 0, but not
-1 or +1. We are not on daylight saving currently. I believe this manifests
itself by the mail program not being able to process the queues because the
"time" has not arrived to process the mail queue.

You may want to check this behaviour out yourself. I have run the code on a
sun and the behaviour is quite different on Solaris.

====

Richard Quan
Tech Support - CSF Melbourne
[Posted by WWW Notes gateway]

void main (void)
{
  time_t time_value, time_get;
  struct tm time_struct;
  char buf[30];

  memset (buf, 0, 30);
  time_value = 0;
  ctime_r (&time_value, buf, 30);

  printf ("ctime_r get \"%s\"\n", buf);

  time_struct.tm_year = 1970 - 1900;
  time_struct.tm_mon = 1 - 1;
  time_struct.tm_mday = 1;
  time_struct.tm_hour = 10;
  time_struct.tm_min = 0;
  time_struct.tm_sec = 0;

  time_struct.tm_isdst = 1;

  printf ("time_strct.tm_year = %d\n", time_struct.tm_year);
  printf ("time_strct.tm_mon = %d\n", time_struct.tm_mon);
  printf ("time_strct.tm_mday = %d\n", time_struct.tm_mday);
  printf ("time_strct.tm_hour = %d\n", time_struct.tm_hour);
  printf ("time_strct.tm_min = %d\n", time_struct.tm_min);
  printf ("time_strct.tm_sec = %d\n", time_struct.tm_sec);
  printf ("time_strct.tm_isdst = %d\n", time_struct.tm_isdst);

  time_get = mktime (&time_struct);

  printf ("mktime return %d\n", time_get); 
}
>---------------------------------------------------------------------------
----
># cc time.c
># ./a.out
>ctime_r get "Thu Jan  1 10:00:00 1970
>"
>time_strct.tm_year = 70
>time_strct.tm_mon = 0
>time_strct.tm_mday = 1
>time_strct.tm_hour = 10
>time_strct.tm_min = 0
>time_strct.tm_sec = 0
>time_strct.tm_isdst = 1
>mktime return -3600
>
>

[Posted by WWW Notes gateway]