A function that calculates the difference between 2 dates.  It is very similar to the datediff function available in Visual Basic.


function datediff($interval, $datefrom, $dateto, $using_timestamps = false) {

if (!$using_timestamps) {

$datefrom = strtotime($datefrom, 0);

$dateto = strtotime($dateto, 0);

}

$difference = $dateto - $datefrom; // Difference in seconds

switch($interval) {

case 'yyyy': // Number of full years

$years_difference = floor($difference / 31536000);

if (mktime(date("H", $datefrom), date("i", $datefrom), date("s", $datefrom), date("n", $datefrom), date("j", $datefrom), date("Y", $datefrom)+$years_difference) > $dateto) {

$years_difference--;

}

if (mktime(date("H", $dateto), date("i", $dateto), date("s", $dateto), date("n", $dateto), date("j", $dateto), date("Y", $dateto)-($years_difference+1)) > $datefrom) {

$years_difference++;

}

$datediff = $years_difference;

break;

case "q": // Number of full quarters

$quarters_difference = floor($difference / 8035200);

while (mktime(date("H", $datefrom), date("i", $datefrom), date("s", $datefrom), date("n", $datefrom)+($quarters_difference*3), date("j", $dateto), date("Y", $datefrom)) < $dateto) {

$months_difference++;

}

$quarters_difference--;

$datediff = $quarters_difference;

break;

case "m": // Number of full months

$months_difference = floor($difference / 2678400);

while (mktime(date("H", $datefrom), date("i", $datefrom), date("s", $datefrom), date("n", $datefrom)+($months_difference), date("j", $dateto), date("Y", $datefrom)) < $dateto) {

$months_difference++;

}

$months_difference--;

$datediff = $months_difference;

break;

case 'y': // Difference between day numbers

$datediff = date("z", $dateto) - date("z", $datefrom);

break;

case "d": // Number of full days

$datediff = floor($difference / 86400);

break;

case "w": // Number of full weekdays

$days_difference = floor($difference / 86400);

$weeks_difference = floor($days_difference / 7); // Complete weeks

$first_day = date("w", $datefrom);

$days_remainder = floor($days_difference % 7);

$odd_days = $first_day + $days_remainder; // Do we have a Saturday or Sunday in the remainder?

if ($odd_days > 7) { // Sunday

$days_remainder--;

}

if ($odd_days > 6) { // Saturday

$days_remainder--;

}

$datediff = ($weeks_difference * 5) + $days_remainder;

break;

case "ww": // Number of full weeks

$datediff = floor($difference / 604800);

break;

case "h": // Number of full hours

$datediff = floor($difference / 3600);

break;

case "n": // Number of full minutes

$datediff = floor($difference / 60);

break;

default: // Number of full seconds (default)

$datediff = $difference;

break;

}

return $datediff;

}

$interval can be:

yyyy – Number of full years

q – Number of full quarters

m – Number of full months

y – Difference between day numbers

(eg 1st Jan 2004 is “1″, the first day. 2nd Feb 2003 is “33″. The datediff is “-32″.)

d – Number of full days

w – Number of full weekdays

ww – Number of full weeks

h – Number of full hours

n – Number of full minutes

s – Number of full seconds (default)

$datefrom – must be a date: timestamp or a date in string format, something like this: 3-5-2010
$dateto – similar to $datefrom
$using_timestamps – boolean, specifies if timestamps are given in $datefrom and $dateto parameters or not