Question

Ok, so looking at this code:

$accountMask = substr($transaction['cc_number'], strlen($transaction['cc_number'])-4); 

I think it takes a number like this: 1234567890
And turns it into this: 123456

Am I crazy to think that the code is actually doing this: 7890 ??

In my opinion, if I wanted to show just the last 4 digits of a number like a CC number, I would do this:

$accountMask = substr($transaction['cc_number'], -4); 

Right?

Answer 1

Both of your examples do the same thing. As per the comments check out the documentation on substr()

Particularly the second parameter:

If start is non-negative, the
returned string will start at the
start’th position in string, counting
from zero. For instance, in the string
‘abcdef’, the character at position 0
is ‘a’, the character at position 2 is
‘c’, and so forth.

If start is negative, the returned
string will start at the start’th
character from the end of string.

If string is less than or equal to
start characters long, FALSE will be
returned.