PHP 5.3.2 DateTime diff() issue
It seems that PHP 5.3.2 ( 5.3.2-1ubuntu4.10 ) has a small issue when using the DateTime diff() method.
Got this code:
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< ?php $mode = 'D'; $back = 1; $start = new \DateTime(); $start->setTime(0, 0); $start->sub(new \DateInterval('P'.$back.$mode)); $end = new \DateTime(); $end->setTime(0, 0); if( $back > 0 ) { $end->sub(new \DateInterval('P'.($back-1).$mode)); } else { $end->add(new \DateInterval('P1'.$mode)); } echo $start->format('Y-m-d H:i:s') . "\n"; echo $end->format('Y-m-d H:i:s') . "\n"; $dt = $start->diff($end); echo $start->format('Y-m-d H:i:s') . "\n"; echo $end->format('Y-m-d H:i:s') . "\n"; $differenceDays = $dt->format('%a'); echo $differenceDays."\n"; ?> |
This code results in:
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2011-12-03 00:00:00 2011-12-04 00:00:00 2011-12-02 00:00:00 2011-12-04 00:00:00 2 |
It seems the diff statement changes the starting date to a date before. This is kind of an issue, i need that difference in a project between days, weeks, months and even years. And the issue get’s worse if you use weeks (the difference becomes 14 days instead of 7) in the interval or months (61 instead of 30 or 31). So i decided to use a quickfix to calculate the difference, cause this was not working…
The workaround needed to change depending on the mode variable (day, week, month or year). For day and week it could just be 1 and 7 days, but the amount of days in a month and years changes per month and per year (leap years). So i came up with:
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< ?php switch($mode) { case "day": $differenceDays = 1; break; case "week": $differenceDays = 7; break; case "month": $differenceDays = date('t',$start->getTimestamp()); break; case "year": $differenceDays = 365; if( date('L',mktime(0,0,0,1,1,$start->format('Y'))) == 1 ) { $differenceDays++; } break; } ?> |
I decided to use the mktime function, because the getTimestamp() gave some issues concerning timezones (i think ;))
Update
Dries Verachtert pointed me to a comment on the page of the DateTime sub method. The short of it:
If you use diff() after sub(), the effects of the sub() will be repeated on the date object.
It doesn’t matter if the object is the one diffed or doing the diffing (i.e. which object you call diff() from).
Note that using add() instead of sub() does NOT have the same effect.
This is particularly undesirable — in this example you make a datetime, use sub() to make it a relative time in the past, and then date->diff() to confirm the difference. But the diff() inadvertendly makes the difference 2x.
Strange issue, but i can tell you it’s fixed in 5.3.3, as i have running that on an internal test server, and the code does a perfect job on that.
