CODEWITHSUNDEEP
phptimestamp
codepuppy
codepuppy

Reputation: 1140

php - timestamp - interval between days not always 86400 seconds - why?

Supplementry Question to timestamp - php incrementing time stamp error

Whilst accepting that class DateTime may provide a resolution to my original query there remains the unexplained variance in the timestamps. I really would like to understand this variance, whether there are other such timestamp "adjustments" and how they arise.

Please consider the following:

/*
 * test time stamp variances
 */

$time_Stamp_1 = mktime(0,0,0,10,15,2012);echo "15/10/12: " . $time_Stamp_1;
$time_Stamp_2 = mktime(0,0,0,10,16,2012);echo "<br/>16/10/12: " . $time_Stamp_2 . "increment= " . ($time_Stamp_2 - $time_Stamp_1); 
$time_Stamp_3 = mktime(0,0,0,10,17,2012);echo "<br/>17/10/12: " . $time_Stamp_3 . "increment= " . ($time_Stamp_3 - $time_Stamp_2);
$time_Stamp_4 = mktime(0,0,0,10,18,2012);echo "<br/>18/10/12: " . $time_Stamp_4 . "increment= " . ($time_Stamp_4 - $time_Stamp_3);
$time_Stamp_5 = mktime(0,0,0,10,19,2012);echo "<br/>19/10/12: " . $time_Stamp_5 . "increment= " . ($time_Stamp_5 - $time_Stamp_4);
$time_Stamp_6 = mktime(0,0,0,10,20,2012);echo "<br/>20/10/12: " . $time_Stamp_6 . "increment= " . ($time_Stamp_6 - $time_Stamp_5);
$time_Stamp_7 = mktime(0,0,0,10,21,2012);echo "<br/>21/10/12: " . $time_Stamp_7 . "increment= " . ($time_Stamp_7 - $time_Stamp_6);
$time_Stamp_8 = mktime(0,0,0,10,22,2012);echo "<br/>22/10/12: " . $time_Stamp_8 . "increment= " . ($time_Stamp_8 - $time_Stamp_7);
$time_Stamp_9 = mktime(0,0,0,10,23,2012);echo "<br/>23/10/12: " . $time_Stamp_9 . "increment= " . ($time_Stamp_9 - $time_Stamp_8);
$time_Stamp_10 = mktime(0,0,0,10,24,2012);echo "<br/>24/10/12: " . $time_Stamp_10 . "increment= " . ($time_Stamp_10 - $time_Stamp_9);
$time_Stamp_11 = mktime(0,0,0,10,25,2012);echo "<br/>25/10/12: " . $time_Stamp_11 . "increment= " . ($time_Stamp_11 - $time_Stamp_10);
$time_Stamp_12 = mktime(0,0,0,10,26,2012);echo "<br/>26/10/12: " . $time_Stamp_12 . "increment= " . ($time_Stamp_12 - $time_Stamp_11);
$time_Stamp_13 = mktime(0,0,0,10,27,2012);echo "<br/>27/10/12: " . $time_Stamp_13 . "increment= " . ($time_Stamp_13 - $time_Stamp_12);
$time_Stamp_14 = mktime(0,0,0,10,28,2012);echo "<br/>28/10/12: " . $time_Stamp_14 . "increment= " . ($time_Stamp_14 - $time_Stamp_13);
$time_Stamp_15 = mktime(0,0,0,10,29,2012);echo "<br/>29/10/12: " . $time_Stamp_15 . "increment= " . ($time_Stamp_15 - $time_Stamp_14);

Reports:

15/10/12: 1350255600
16/10/12: 1350342000increment= 86400
17/10/12: 1350428400increment= 86400
18/10/12: 1350514800increment= 86400
19/10/12: 1350601200increment= 86400
20/10/12: 1350687600increment= 86400
21/10/12: 1350774000increment= 86400
22/10/12: 1350860400increment= 86400
23/10/12: 1350946800increment= 86400
24/10/12: 1351033200increment= 86400
25/10/12: 1351119600increment= 86400
26/10/12: 1351206000increment= 86400
27/10/12: 1351292400increment= 86400
28/10/12: 1351378800increment= 86400
29/10/12: 1351468800increment= 90000

Hence:

> 15/10/2012 1350255600 + 604800 does increment 1 week to 22/10/2012 ..
> 22/10/2012 1350860400 + 604800 does not increment 1 week to 29/10/2012
> because although this results in 1351465200 which should be 29/10/2012
> you can see from the above that it resolves to 28/10/2012 because for
> some unexplained reason an extra hour 3600sec has been added to the
> time stamp for 29/10/2012.

I want to know because from my reading of the documentation mktime should create a timestamp just as valid as say strtotime or DateTime.

Indeed using class DateTime method getTimestamp

28/10/2012 = 1351378800 29/10/2012 = 1351468800 an increment of 90000

So once again an hour has been added implying that I am correct in this assumption.

Obviously the class can deal with this. BUT no where up until this point has there been any mention of the fact that incrementing a timestamp however it is generated could result in an issue... thus making the use of the DateTime class or another approach mandatory to avoid issues such as have been encountered.

If I have to convert the code you use the class so be it. But I would like to know why this is necessary.

Upvotes: 4

Views: 5172

Answers (2)

Joni
Joni

Reputation: 111289

Due to a daylight savings shift, 28/10/12 has an extra hour in your timezone. There are 25 hours between midnight 28/10 and midnight 29/10.

You will also find a day with 23 hours in spring.

If this is not what you expect, change the timezone to something that has no DST. UTC is one option:

php > echo mktime(0,0,0,10,29,2012) - mktime(0,0,0,10,28,2012);
90000
php > ini_set('date.timezone', 'UTC');
php > echo mktime(0,0,0,10,29,2012) - mktime(0,0,0,10,28,2012);
86400

Upvotes: 7

alanmanderson
alanmanderson

Reputation: 8210

I'm going to take a stab at this. October 29th is exactly 1 week before daylight savings time (unless you are in a country with a different daylight savings time). But falling back 1 hour would cause a day to have 1 more hour.

Upvotes: 1

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