UNIX TIMESTAMP

Anon

Is here anybody who can say exactly what UNIX TIMESTAMP is and describe its relation with Date and Time functions group (especially gm...), with daylight saving time and with local time zone?
Below there is a code, where comments are result of executing on my PC, (my GMT Offset = +2 hours = +7200 sec.). Plese, see this code carefully before doing any findings.
Some trubles appear as with summer (daylight saving time) as with winter time. Especailly is concerns the gmmktime è gmdate functions.

$df="d.m.Y - H:i:s (Z)";

$t=mktime(0,0,0,1,2,1970);
echo " Make 02.01.1970 - 00:00:00 (Local): ",
"Timestamp: $t ", // 79200
"GMT: ", gmdate($df,$t), " ", // 01.01.1970 - 22:00:00 (7200)
"Local: ", date($df,$t), " ", // 02.01.1970 - 00:00:00 (7200)
"---------------------------------------- ";

$t=gmmktime(0,0,0,1,2,1970);
echo " Make 02.01.1970 - 00:00:00 (GMT): ",
"Timestamp: $t ", // 82800 (Why !=86800 ?)
"GMT: ", gmdate($df,$t), " ", // 01.01.1970 - 23:00:00 (7200)
"Local: ", date($df,$t), " ", // 02.01.1970 - 01:00:00 (7200)
"---------------------------------------- ";

$t=mktime(0,0,0,7,20,1970);
echo " Make 02.07.1970 - 00:00:00 (Local): ",
"Timestamp: $t ", // 17269200
"GMT: ", gmdate($df,$t), " ", // 01.07.1970 - 21:00:00 (7200)
"Local: ", date($df,$t), " ", // 02.07.1970 - 00:00:00 (10800)
"---------------------------------------- ";

$t=gmmktime(0,0,0,7,20,1970);
echo " Make 02.07.1970 - 00:00:00 (GMT): ",
"Timestamp: $t ", // 17280000 (=86400*200)
"GMT: ", gmdate($df,$t), " ", // 02.07.1970 - 00:00:00 (7200)
"Local: ", date($df,$t), " ", // 02.07.1970 - 03:00:00 (10800)
"---------------------------------------- ";

Anon

If you read the documentation you'll find that there's one more argument to pass to mktime and gmmktime. Set it to 1 to indicate daylight savings is in effect, 0 means it's not. The default is -1 which means it's unknown. Try adding that argument and seeing if that makes a difference.

Hank

Anon

Thanks.
But, of course, I know about this parameter and I know what affect it makes.
But, by default (when it is -1) the correct value is taken automaticaly, and [gm]date(0,0,0,1,2,1970) = [gm]date(0,0,0,1,2,1970,0), and [gm]date(0,0,0,7,20,1970) = [gm]date(0,0,0,7,20,1970,1).
If you study the code more carefully (try that code on your PC), you'll see what question is.
Could you explain me this result:
<?
$df="d.m.Y - H:i:s (Z)";
$t=gmmktime(0,0,0,1,2,1970);
echo " Make 02.01.1970 - 00:00:00 (GMT): ",
"Timestamp: $t ", // 82800 (Why !=86800 ?)
"GMT: ", gmdate($df,$t), " ", // 01.01.1970 - 23:00:00 (7200)
"Local: ", date($df,$t), " ", // 02.01.1970 - 01:00:00 (7200)
?>

Anon

Hmm, very interesting.
Maybe, it's a bug?