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There are some external restrictions on the implementation provided by this plugin:

    * using other timezones than that of the server only works on UNIX-like systems, as it is implemented by modifying the TZ variable in the environment
    * changing TZ is not available in PHP?s safe mode
    * when TZ is changed, only a success message is displayed instead of the full form: this is due to PHP only implementing the old putenv interface for the environment (not the POSIX unsetenv(3) interface)

djmaze(AT)cpgnuke(.)com
27-Mar-2005 11:53
PHP date, strftime and mktime functions are DST sensitive
This means if the server is setup to be US GMT-5 and DST sensitive then the mentioned functions add, extract or do nothing with the current DST.

Without a given timestamp:
   - date() uses the current server time.
     This is DST affected if the server uses DST settings
   - gmdate() uses the current GMT time, it extracts server GMT & DST.

With a given timestamp:
   - date() is affected if the server uses DST settings
     * if current time is DST but the given time isn't then DST is extracted
     * if current time isn't DST but the given time is then DST is added
   - gmdate() is affected, it extracts server GMT & DST on the given timestamp

So for example $timestamp is a GMT based time.
You modify the $timestamp for a "member" his personal timezone and dst.
The member has setup GMT-5 and DST sensitive
You add his GMT-5 to the $timestamp and check if the $timestamp is in DST or not

Then all the above functions  are screwed in normal use.

<?php

$timestamp = 1122814800; // 07/31/05 13:00:00 GMT
$user_gmt = -5;
$user_dst = 1;

$timestamp += ($user_gmt*3600); // to user time
$timestamp += 3600; // user time is in DST

echo date("H:i:s",$timestamp);
echo gmdate("H:i:s",$timestamp);

?>

If server is GMT+0 in summer (DST is on) the above outputs

08:00:00
07:00:00

If server is GMT+0 in winter (DST is off) the above outputs
09:00:00
08:00:00

If server is GMT-5 in winter (DST is off) the above outputs
09:00:00
03:00:00