defining the negative start parameter in substr as a variable

Is using the following correct for defining the negative start parameter for a substr, because its the only way i know how to get it to retur the correct result.

$start == (-44); 
or
$start == (int) -44;

$pair = substr($s开发者_高级运维tr, $start, 4);

the substr call is valid, the only error in your code (posted here) is the == operator.

It should be:

$start = -44;
$pair = substr($str, $start, 4)

Also is the start value -44 the 44th character from start or the end. The above code considers -44 to mean 44th character from end of string.

One more error you could run into is if the length of $str is less than 44.

You can just add a - before an expression (including a variable) to invert its sign:

$pair = substr($str, -$start, 4);

Or

$pair = substr($str, -44, 4);