mktime() says 30.958 days in month of March

[pnj]

Here is the code.  The goal is to count the number of days between two days passed in mysql yyyy-mm-dd format.

[code]function date_sub ($d1, $d2) {
  $t1 = mktime (0, 0, 0, substr($d1, 5, 2), substr($d1, 8, 2), substr($d1, 0, 4));
  $t2 = mktime (0, 0, 0, substr($d2, 5, 2), substr($d2, 8, 2), substr($d2, 0, 4));

  $diff = ($t1 - $t2);
  return ($diff / (60 * 60 * 24));
}
/**** END FUNCTION *************************/

echo date_sub ("2006-03-01", "2006-02-01") . '<br>';
echo date_sub ("2006-04-01", "2006-03-01") . '<br>';
echo date_sub ("2006-05-01", "2006-04-01") . '<br>';
echo date_sub ("2006-06-01", "2006-05-01") . '<br>';
echo date_sub ("2006-07-01", "2006-06-01") . '<br>';
[/code]

The code outputs this:

[code]28
30.9583333333
30
31
30[/code]

What's with the 30.958 days in March instead of 31?  I realize I can get around the problem with (int)($d+0.5), but I wonder if this strange behavior implies that I am using the date function incorrectly...

Thanks
pnj

[Daniel0]

I don't know why it would do that. You can use the round function to fix it.

What I think would be a better solution would be to use timestamps: [code]<?php
function date_sub($d1,$d2)
{
return round(($d1-$d2)/60/60/24,0);
}

echo date_sub(*timestamp one*, *timestamp two*);
?>[/code]

[pnj]

But is there a better way to turn those mysql date fields into timestamps besides using mktime()?  I don't think it's feasible to use timestamps in the database, as it is a date field that I am trying to record.

cheers
pnj

[kenrbnsn]

Have you looked at the [url=http://www.php.net/strtotime]strtotime()[/url] function.

Ken

[pnj]

ah, a highly interesting function, thank you.
-pnj