error

My script looks like this:

$infile = "input.txt";

$fp = fopen($infile, "r") or die("Couldn't open $infile");

while(!feof($fp)){
 $line = fgets($fp);
 $trimmed = trim($line);
 list($start,$middle,$end) = split(' ', $trimmed);
 list($middle_start, $middle_end) = split(':', $middle);
}
fclose($fp);

All I get is errormessages:

Notice: Undefined offset:  1 in C:\Apache\Apache2\htdocs\stuff\i3.php on
line 10
Notice: Undefined offset:  1 in C:\Apache\Apache2\htdocs\stuff\i3.php on
line 10

and so on.

What function gives that errormessage?
Should I put quotes somewhere.

It works for a single line.
The line looks like this: "Name. 1:1. Some text."

If you could help, I would appreciate it.