How can I create a function that can figure out the previous month's last day dates?

Answer 1

Why not just take the timestamp of the first day of the month, and subtract 24 hours from it and then use date('d', $timestamp); ? Also, if you have a timestamp in that month, date('t', $timestamp); will get the number of days in the month for you.

A quick example:

// sets to 3am, first day of month, 3am helps us avoid DST issues with subtracting hours    
$monthStart = mktime(3,0,0,date('n'),1,date('Y')); 
$thisMonth = date('n', $monthStart);

// rewind to the sunday before- date('w') is the "weekday" 0 based    
$date = $monthStart - (date('w',$monthStart) * 60 * 60 * 24);     

while ($date<$monthStart || date('n', $date) == $thisMonth)
{
  echo "<tr>";
  for ($x=0; $x<7; $x++) {
    echo "<td";
    if (date('n', $date) != $thisMonth) echo " class='notMonth'";
    echo ">";
    echo date("j", $date);
    echo "</td>";
    $date += 60*60*24;
  }
  echo "</tr>\n";
}

Answer 2

Perhaps this can help?

cal_days_in_month()

(Edited to include inshalla's feedback)

Answer 3

Assuming $day is a UNIX timestamp:

// gets you the first of the month
$date = getdate(mktime(0, 0, 0, date('n', $day), 1, date('Y', $day)));

From here, do one of these:

$lastDayOfPrevMonth = strtotime('-1 day', $date[0]);

// or, better, get the first day "in the grid" (assuming week starts on Sunday)
$date = strtotime("-$date[wday] days", $date[0]);

I don't want to harp on it, but have you looked at my previous answer? That's a more robust way to build a calendar instead of all this special case checking.

Answer 4

Take a look at the source of PHP-Calender-Class Project:

http://code.google.com/p/php-calendar-class/

class source: http://code.google.com/p/php-calendar-class/source/browse/trunk/calendar.class.php

It may give you some insight on the problem.

Answer 5

Using cal_days_in_month(), How about adding the following code:

if ($day < 1) {
  echo '<td>' . ($day + cal_days_in_month(
     CAL_GREGORIAN,date_format("n",
         date_add(date_create(),"P-1M")))) . ' </td>'; // for example,-1 + 30 = 29th
}

EDITED: Added the date_format function

Answer 6

Wait a minute... your month name at the top is wrong! It says "August 2009", but the month has 30 days and the weekdays are right for September 2009!

You need to repair the current month first, before worrying about other months.