Thanks for replying.
You may have found the problem (partially)...

On our AIX machine, the 'Europe' folder does not exist.
However we have a file called GB-Eire under the /usr/share/lib/zoneinfo directory.

When I set TZ to GB-Eire, I get the correct output (ie. same output as when I set TZ to Posix format GMT0BST,M3.5.0,M10.5.0)

I changed the strftime and the timeString variables as follows:

Code:

 char timeString[30];
strftime( timeString, sizeof( timeString), "%d-%b-%Y %H:%M:%S", &timeHolder);

<snip>
Secs: 3599 Time: 01-Jan-1970 00:59:59
Secs: 3600 Time: 01-Jan-1970 01:00:00
Secs: 3601 Time: 01-Jan-1970 01:00:01
<snip>

But on our Solaris machine, we have the 'Europe/London' folder and file, a GB file and a GB-Eire file. Setting TZ to any of these does not work. All give:

<snip>
Secs: 3599 Time: 01-Jan-1970 01:59:59
Secs: 3600 Time: 01-Jan-1970 02:00:00
Secs: 3601 Time: 01-Jan-1970 02:00:01
<snip>

Which is different from what I get when I set TZ to Posix format : GMT0BST,M3.5.0,M10.5.0

<snip>
Secs: 3599 Time: 01-Jan-1970 00:59:59
Secs: 3600 Time: 01-Jan-1970 01:00:00
Secs: 3601 Time: 01-Jan-1970 01:00:01
<snip>

Strange...so it looks like it might work correctly when I get the 'Europe/London' file under zoneinfo folder on AIX (will need to test this)...but not sure why it does not work on Solaris.

---------- Post updated at 01:45 PM ---------- Previous update was at 01:09 PM ----------

Thanks for replying.
I agree that the DST does not apply in winter in London. But I would expect that if I set TZ in Posix (GMT0BST,M3.5.0,M10.5.0) or Olson (Europe/London) formats, I should get the same output (this is on Solaris where I have the '/usr/share/lib/zoneinfo/Europe/London' file).

When I try starting at 1367275312 onwards it does match. But then these are when DST is ON and it always works correctly (as in both posix/olson outputs match) when DST is ON. Same when I set to 8598706 (when DST is ON and in the 1970s):

Secs: 8598706 Time: 10-Apr-1970 13:31:46

On both formats, I get the same answer.

So the problem exists only when DST is off and looking at my reply to 'Shamrock' above, maybe only on Solaris (as AIX seems to work for GB, EB-Eire and if I have 'Europe/London' may work too).