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Open Source Technologies

Notes Two more date functions are available: gmmktime() and mktime(). Both functions create a
timestamp based on parameters passed when the function is called. The difference between
the two functions is that gmmktime() treats the date/time parameters passed as a Greenwich
Mean Time (GMT), while parameters passed to mktime() are treated as local time. The order of
parameters is not very user friendly, as you can see in the prototype of the following function:

timestamp mktime ( [$hour [, $minute [, $second [, $month [, $day [,
‘$year [, $is_dst]]]]]]])

The particularly weird order of the parameters.

All parameters are optional. If any parameter is not included, the “current” value is used,
depending on the current date and time. The last parameter, is_dst, controls whether the date
and time parameters that are passed to the function are DST-enabled or not. The default value
for the parameter is -1, which signals PHP to determine for itself whether the date falls into the
range when DST is observed. Here is an example:

Example: <?php
/* mktime with a date outside the DST range */
echo date(“Ymd H:i:s”, mktime(15, 16, 17, 1, 17, 2004)). “\n”;
echo date(“Ymd H:i:s”, mktime(15, 16, 17, 1, 17, 2004, 0)). “\n”;

echo date(“Ymd H:i:s”, mktime(15, 16, 17, 1, 17, 2004, 1)). “\n”;
/* mktime with a date inside the DST range */

echo date(“Ymd H:i:s”, mktime(15, 16, 17, 6, 17, 2004)). “\n”;
echo date(“Ymd H:i:s”, mktime(15, 16, 17, 6, 17, 2004, 0)). “\n”;
echo date(“Ymd H:i:s”, mktime(15, 16, 17, 6, 17, 2004, 1)).

“\n\n”;

?>
The first three calls “make” a timestamp for January 17, in which no DST is observed. Therefore,
setting the $is_dst parameter to 0 has no effect on the returned timestamp. If it’s set to 1, though,
the timestamp will be one hour earlier, as the mktime() function converts the DST time (which
is always one hour ahead of non-DST). For the second set of mktime() calls, we use June 17 in
which DST is observed. Setting the $is_dst parameter to 0 now makes the function convert the
time from non-DST to DST and, thus, the returned timestamp will be one hour ahead of the
result of the first and third calls. The output is

20040217 15:16:17
20040217 15:16:17
20040217 14:16:17

20040617 15:16:17
20040617 16:16:17

20040617 15:16:17

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