Question

I’m trying to do some very basic time math – basically, given inputs of time and distance, calculate the speed. I chose to use strtotime() to convert the time inputs into seconds – but I’m getting some bizarre results.

For example, given this sample program:

<?php
$t1 = strtotime("3:15:00",0);
$t2 = strtotime("1:00:00",0);
$t3 = strtotime("2:00:00",0);
$t4 = strtotime("9:00:00",0);

echo $t1 . "\n";
echo $t2 . "\n";
echo $t3 . "\n";
echo $t4 . "\n";
?>

Why do I get these results?

$ php test.php 
-56700
-64800
-61200
-36000

Update:

Since no one said it explicitly, let me explain the bug in the above function. I had assumed that passing a time of zero to strtotime() would cause it to generate time stamps derived from midnight, 12/31/1969, UTC – which sounds odd, but would work for my purposes.

What I hadn’t counted on was that strtotime() takes time zones into account when converting strings, and my server is apparently 5 hours behind UTC. On top of that, because of the time zone shift, PHP then interprets the times as relative to the day before the epoch which means it is interpreting my times as occurring relative to December 30th, 1969 instead of the 31st, resulting in negative numbers…

It appears that Eugene is correct – if I want to calculate just the elapsed time, I can’t use the built in time functions.

Answer 1

If you want to do something like that, I think you want to just do some math on the time strings themselves and convert them to a number of seconds, like this:

<?php
function hmstotime($hms)
{
    list($hours, $minutes, $seconds) = explode(":",$hms);
    return $hours * 60 * 60 + $minutes * 60 + $seconds;
}
?>