发现两次之间的差异。 （PHP / MySQL的）

Question

I am trying to identify the duration of something by finding the difference between the start time and the end time.

//bring date & time input into mysql datetime format for query

$t_start_datetime = date('Y-m-d G:i:s' ,strtotime($_POST['t_date'].' '.$_POST['t_start'].' '.$_POST['s_ampm']));
$t_end_datetime = date('Y-m-d G:i:s' ,strtotime($_POST['t_date'].' '.$_POST['t_end'].' '.$_POST['e_ampm']));

// get duration value of test by finding the difference between the start and end time.
$end_time= strtotime($_POST['t_date'].' '.$_POST['t_start'].' '.$_POST['s_ampm']);
$start_time= strtotime($_POST['t_date'].' '.$_POST['t_end'].' '.$_POST['e_ampm']);

$temp = $end_time - $start_time;

echo date('G:i:s', $end_time);
echo date('G:i:s', $start_time);
//here is the duration
echo date('G:i:s', abs($temp));

So lets say the value of start_time was 6:00:00 and end_time 7:45:00 my duration is coming out as 2:45:00 :S

It's always an hour more than the actually difference.

What am I doing wrong? Please enlighten me.

Thanks

Answer 1

$end_time   = new DateTime($_POST['t_date'].' '.$_POST['t_send'].' '.$_POST['s_ampm']);
$start_time = new DateTime($_POST['t_date'].' '.$_POST['t_start'].' '.$_POST['e_ampm']);
$diff       = $end_time->diff($start_time);
echo $diff->format('%H:%I:%S');

You cannot use the regular date formatting here as it'll treat $temp as a UNIX timestamp and will therefore be influenced by timezones and issues such as DST, e.g.

$e = strtotime('2011-03-31 12:30:00'); // 1301567400
$s = strtotime('2011-03-31 10:55:00'); // 1301561700
$d = $e - $s;                          //       5700
echo date(DateTime::RSS, $d);
// Thu, 01 Jan 1970 02:35:00 +0100
echo date('G:i:s', $d);
// 2:35:00

To circumvent this problem you could use

$d = new DateTime('@'.$d);
echo $d->format('G:i:s');

because DateTime does not take timezones into account when using it with timestamps.

EDIT

As the OP uses PHP 5.1.x there is another solution:

$end_time   = strtotime($_POST['t_date'].' '.$_POST['t_start'].' '.$_POST['s_ampm']);
$start_time = strtotime($_POST['t_date'].' '.$_POST['t_end'].' '.$_POST['e_ampm']);
$temp       = abs($end_time - $start_time);
echo gmdate('G:i:s', $temp);

But this only works if $start_time and $end_time are within a 24 hour timespan (as do all solutions presented except for the first one).

The manual solution (but it works in general and does not rely on any date-time-handling

$end_time   = strtotime($_POST['t_date'].' '.$_POST['t_start'].' '.$_POST['s_ampm']);
$start_time = strtotime($_POST['t_date'].' '.$_POST['t_end'].' '.$_POST['e_ampm']);
$temp       = abs($end_time - $start_time);

$hours   = floor($temp / 3600);
$minutes = floor( ($temp - $hours*3600) / 60 );
$seconds = $temp - $hours*3600 - $minutes*60;
$diff    = sprintf('%d:%02d:%02d', $hours, $minutes, $seconds);

This can easily be extended to days and weeks. Months and years will be difficult because they change their length throughout a year or throughout decades.