php usort error message

Question

I have a class called Link with a function called Compare. When I runt this code I keep getting an error message

foreach($filearray as $k=>$v)  
{  
$website = new Link($v);  
$links[] = $website;  
}  
usort($links, array("Link","compare"));  

But I get an error message and I cant figure out why...

"Warning: usort() [function.usort]: The argument should be an array"

Answer 1

If $links haven't been initialized as an array, when $filearray is empty, $links remains null.

Add $links = array(); before the loop.

Answer 2

Second parameter is the comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

Check the below article http://php.net/manual/en/function.usort.php