[RESOLVED] Time Difference

LoganK

I'm writing an application which logs time spent on a certain job, and I'v having trouble getting PHP to correctly calculate the number of hours spent.

For example, if I worked from 8:00 a.m. to 4:00 p.m., currently it would look like this (military time):

$start = 800;
$end = 1600;

$total = $end-$start;

And $total = 600, which is correct, because I spent 6 hours on the job. But if I start work at 8:30, then (in military time):

$start = 830;
$end = 1600;

$total = $end-$start;

And now $total = 770, which obviously 7 hours and 70 minutes isn't correct. All I need is to be able to determine the difference between two times within one day; I'm not doing more than one day because then it's even more complex. I'm just trying to get it to know that if I start work at 8:30 a.m., and end work at 4:00 p.m., that I worked for a toal of 5 1/2 hours. Does anyone know how?

TheDefender

Use [man]date[/man] and [man]mktime[/man] to convert the times to seconds since the Unix epoch (using the "U" format character in the date function). Then subtract your times like normal. The end result is a value in seconds. From there, you can use a simple seconds to hours and minutes conversion to get the time difference. Write your code using the tips I've provided, and post back if you need help with tweaking it or getting it to work.

LoganK

TheDefender wrote:
Use [man]date[/man] and [man]mktime[/man] to convert the times to seconds since the Unix epoch (using the "U" format character in the date function).

I understand everything but this. How do I use the two together? This is what I have so far...

$start = date("U", mktime(8));
$end = date("U", mktime(16)); // Do I use military time here? 

$total = $end - $start;

$total = $total / 60;
$total = $total / 60;

The problem is that if for $end, I specify date("U", mktime(16, 30)) (for 4:30), it gives me as a final output 8.33333..., although in reality it was 8 1/2 hours, or 8.5.

Did I do something wrong?

TheDefender

$start = date("U", mktime(8,0,0,7,9,2005)); // You need to specify all of the parameters for mktime
$end = date("U", mktime(16,30,0,7,9,2005)); // You need to specify all of the parameters for mktime
$totalseconds = $end-$start;

echo ($totalseconds/3600); // divide by 3600 seconds (3600 seconds per hour)
// Outputs 8.5

TheDefender

Do note, that you may want to [man]round[/man] your final answer to 2 significant digits because 8 hours and 20 minutes would output 8.33333333

Oh, one other thing from the manual for mktime:

Negative timestamps are not supported under any known version of Windows. Therefore the range of valid years includes only 1970 through 2038.
Since it sounds like you are dealing with current dates, this shouldn't be an issue anyhow, but thought it would be wise to mention it just in case.

LoganK

I didn't specify all of the parameters because the PHP manual said that PHP would guess any unspecified ones from the local system. Now that you mention it I realize that I assumed PHP would just use the system defaults for the date part; in fact it was probably assigning the system defaults to the minutes and seconds, so my times were changing every second!

As for the rounding, I guess you mean 2 digits in total, not 2 after the decimal point, right? So round($totalseconds, 1) should work. Although, I probably will never use 20s, only 15, 20, and 45 increments. But it's good to note for the future.

Thanks for all your help; I think I have what I need now to continue my project.

P.S. As for the Windows/negative dates, I know about that b/c I got that error when I was first debugging the app earlier today! ;-)

TheDefender

You're welcome. That's correct, the seconds were being assumed, and as a result, they were continuously changing. When I use the mktime function, I don't leave anything to chance. I usually put 0 in for the seconds parameter and feed the month, day and year from parameters I create of the current (or desired date). I figure the more I don't assume, the less headaches I have in the future. It's worked for me so far. 😉

Feel free to post back if you need any more assistance with your project in the future.

LoganK

How do we resolve threads? It looks like the link dissapeared!

laserlight

Until the feature is added to the new messageboard theme/system, you probably have to edit the topic to manually mark the the thread resolved.