Question

I have a start/end times for a calculation I’m trying to do and am having a problem seeing if the end time is before 12AM the day after the start time. Also, I need to calculate how many days past the start time it is.

What I have: Start Date, End Date

What I need:
– How many ‘Midnights’ is the End Date past the Start Date?

Has anyone done anything like this?

Answer 1

This uses PHP 5.3, if you have an earlier version you may need to use unix timestamps to figure out the difference. The number of midnights should be the number of days difference assuming both start and end times have the same time. So setting both to be midnight of their current day setTime(0,0), should make the calculation correct.

Using the DateTime objects.

$start = new DateTime('2011-03-07 12:23:45');
$end = new DateTime('2011-03-08 1:23:45');

$start->setTime(0,0);
$end->setTime(0,0);

$midnights = $start->diff($end)->days;

Without using the setTime() calls, this would result in 0, because there is less than 24 hours between start and end. With the setTime() this results in 1 because now the difference is exactly 24 hours.

The diff() function was introduced in 5.3 along with the DateInterval class. In 5.2 you can still use the DateTime class but will have to work out the total days using the Unix timestamp.

$midnights = ($end->format('U') - $start->format('U')) / 86400

You can wrap that in an abs() function to the order of start/end does not matter.

Note: These functions may need to be tested for cases that involve DST.

A comment in the php date documentation uses round after dividing by 86400 (number of seconds in a day), to counter any issues that could be involved with DST.

An alternative approach with DateTimes would be to create them in the UTC.

$utcTimezone = new DateTimeZone('UTC');
$start = new DateTime('2011-03-07 12:23:45', $utcTimezone);
$end = new DateTime('2011-03-08 1:23:45', $utcTimezone);