Can't use strlen() in a custom script

Content

Is there a reason I can't? 

This works:

$label_one = "This is some text";
$label_two = "This is the second val";
$rows[0][1]->val = $label_one;
$rows[0][2]->val = $label_two;
$rows[0][1]->val = substr($label_two,4,7);

 

This does not:

$label_one = "This is some text";
$label_two = "This is the second val";
$rows[0][1]->val = $label_one;
$rows[0][2]->val = $label_two;
$rows[0][1]->val = strlen($label_two);

Version

Nov 2015