PHP file modified time use GMT offset setting to report correct time

Question

I'm currently reporting file modified time like so:

$this->newScanData[$key]["modified"] = filemtime($path."/".$file);
$modifiedtime = date($date_format." ".$time_format, $this->newScanData[$key]["modified"]);

To me I thought there was nothing wrong with that but a user of my code is reporting the time being 4 hours out. The only reason why I can think of this is because the server is in a different timezone to the user. Each user has a variable I can use $gmt_offset that stores the time zone that user is in. $gmt_offset is stored as a basic float offset.

The server could be in any timezone, not necessarily in GMT-0. The server might not be in the same timezone as the user.

How do I get $modifiedtime to have the correct time for the user in his timezone based on $gmt_offset?

how do you store the timezone of the user? As an integer offset? — Chris Laarman, Jun 09 '11 at 09:42
@Brady but you can define the server's time zone? Or do you need to find it out? — Pekka, Jun 09 '11 at 09:51
@Pekka - It's something PHP will have to find out. This script could be used by a number of people in different countries and the servers residing in different places. — Scott, Jun 09 '11 at 09:54

Salman A · Answer 1 · 2011-06-09T11:01:00.343

filemtime() will return a unix timestamp based on the server's clock. Since you have user to gmt offset available, you must convert the unix timestamp to GMT and then into user's timszone as follows:

<?php
    list($temp_hh, $temp_mm) = explode(':', date('P'));
    $gmt_offset_server = $temp_hh + $temp_mm / 60;
    $gmt_offset_user   = -7.0;
    $timestamp         = filemtime(__FILE__);
    echo sprintf('
        Time based on server time.........: %s
        Time converted to GMT.............: %s
        Time converted to user timezone...: %s
        Auto calculated server timezone...: %s
        ',
        date('Y-m-d h:i:s A', $timestamp),
        date('Y-m-d h:i:s A', $timestamp - $gmt_offset_server * 3600),
        date('Y-m-d h:i:s A', $timestamp - $gmt_offset_server * 3600 + $gmt_offset_user * 3600),
        $gmt_offset_server
    );

    // Output based on server timezone = PKT (+05:00 GMT) and user timezone = PDT (-07:00 GMT)
    // Time based on server time.........: 2011-06-09 03:54:38 PM
    // Time converted to GMT.............: 2011-06-09 10:54:38 AM
    // Time converted to user timezone...: 2011-06-09 03:54:38 AM
    // Auto calculated server timezone...: 5

Chris Laarman · Accepted Answer · 2011-06-09T10:00:29.373

1

What you need is the strtotime() function. Changed date to gmdate, converting your servers time to GMT

For example if you need the time format like 10:00:00

gmdate("H:i:s", strtotime($gmt_offset . " hours"));

More info here:

http://php.net/manual/en/function.strtotime.php

http://php.net/manual/en/function.gmdate.php

edited Jun 09 '11 at 10:00

answered Jun 09 '11 at 09:47

Chris Laarman

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But would this work? What if the server was in GMT-2 and the user was in GMT-4. – Scott Jun 09 '11 at 09:51
This answer was given before i came clear you needed the server's offset too. So it won't work like that. Will edit the answer – Chris Laarman Jun 09 '11 at 09:58
Where do I feed in the `$timestamp` value of `filetime()`? – Scott Jun 09 '11 at 10:03
That would be something like: `gmdate("H:i:s", ($timestamp + ($gmt_offset * 3600)));` – Chris Laarman Jun 09 '11 at 10:10
Thanks XpertEase I came to the same code myself. Just testing now. – Scott Jun 09 '11 at 10:16

score 1 · Answer 3 · answered Jun 09 '11 at 09:54

1

$modifiedtime = date($date_format." ".$time_format, $this->newScanData[$key]["modified"] + ($gmt_offset * 3600));

$gmt_offset should be of type float, not int -- some time zones can have fractional difference, like GMT +09:30 for Adelaide

answered Jun 09 '11 at 09:54

LazyOne

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Here you are assuming the server is in GMT-0? – Scott Jun 09 '11 at 09:56
@Brady: No, here offset will be relative to the server time. You can add additional correction for the server timezone (e.g. `$server_offset`) – LazyOne Jun 09 '11 at 10:00
@LazyOne: and how do you check the timezone of the server time? – Chris Laarman Jun 09 '11 at 10:03
@XpertEase2: Well, if you know where your server is located/which timezone **you** have set up there, then `$server_offset` can be hardcoded/declared as Constant. If you need to calculate it dynamically -- look at [DateTime::getOffset](http://uk.php.net/manual/en/datetime.getoffset.php) – LazyOne Jun 09 '11 at 10:10
Sorry LazyOne but I cannot guarantee that the DateTime class will be available on all servers. – Scott Jun 09 '11 at 10:17
@Brady: DateTime is standard PHP class and is available since PHP v5.2.0 (released 02-Nov-2006) which is obsolete now (only 5.3.x is supported). How old these servers are (in terms of PHP installation) and why would someone still use such old version (< 5.2) if 5.2.x (especially 5.3.x) is definitely faster (no doubts at all)? The only reason -- VERY old LEGACY code. – LazyOne Jun 09 '11 at 10:32
@brady: check my answer. You can use `date("P")` on PHP 5.1.3 and later. – Salman A Jun 09 '11 at 10:37

PHP file modified time use GMT offset setting to report correct time

3 Answers3