How to extract substring by start-index and end-index?

Question

$str = \'HelloWorld\';
$sub = substr($str, 3, 5);
echo $sub; // prints \"loWor\"

I know that substr() takes the first parameter, 2nd parameter is start

Answer 1

Just subtract the start index from the end index and you have the length the function wants.

$start_index = 3;
$end_index = 5;
$sub = substr($str, $start_index, $end_index - $start_index);