need help creating urls with year and month - php

Question

I need to create next and previous link urls
here's a sample
previous
<? echo $_GET['month'].', '.$_GET['year']; // shows 11, 2009
next
where the 2nd segment is the year and the first segment is the month
I've got the month and the year in the GET array, but any ideas how best to do this?
I was thinking prevmonth = month-1, but then if the previous month was a new year, that would get all messed up.

Answer 1

You can use mktime with out-of-range values to do things like this. See the example #2 on the manual page.
e.g. echo date("M-d-Y", mktime(0, 0, 0, 13, 1, 1997)); will give 1998-01-01.

Answer 2

strtotime() makes it pretty easy.
$year = 2009;
$month = 5;
$nextMonth = strtotime('+1 Month', strtotime($year.'-'.$month.'-01'));
echo date('Y/m', $nextMonth);

Answer 3

Fairly easy to catch that sort of logic...? Just inc/dec the year if your month goes out of bounds...
#sanity check inputs
$month=min(max(intval($_GET['month']), 1),12);
$year=intval($_GET['year']);
$prev=array($month-1, $year);
if ($prev[0]==0)
{
$prev[0]=12;
$prev[1]--;
}
$next=array($month+1, $year);
if ($next[0]==13)
{
$next[0]=1;
$next[1]++;
}

Answer 4

I think the easiest way would just be to check for the "previous month < 1" condition and decrement the year. There might be a more clever way to do this, but this is easy enough to understand:
$prevyear = intval($_GET['year']);
$prevmonth = intval($_GET['month']) - 1;
// Check for year rollover.
if ( $prevmonth < 1 ) {
$prevmonth = 12;
$prevyear = $prevyear - 1;
}