Question

I’m having trouble with decreasing a string ID. This is the case:

// given $row[0]['orderid'] = "ORD00389" (varchar)
$nextID = $row[0]['orderid'];
$prevID = $row[0]['orderid'];
$nextID++; // echo 'ORD00390'
$prevID--; // echo 'ORD00388'

What I learned so far is this lovely paragraph:

PHP follows Perl’s convention when dealing with arithmetic operations
on character variables and not C’s. For example, in PHP and Perl $a =
‘Z’; $a++; turns $a into ‘AA’, while in C a = ‘Z’; a++; turns a into
‘[‘ (ASCII value of ‘Z’ is 90, ASCII value of ‘[‘ is 91). Note that
character variables can be incremented but not decremented and even so
only plain ASCII characters (a-z and A-Z) are supported.
Incrementing/decrementing other character variables has no effect, the
original string is unchanged.

Is there any efficient way (built-in function) to decrease that string in PHP?

Answer 1

If it ends in ORD every time you can get rid of the ORD, subtract 1, then put it back together.

$id_num = intval( str_replace( 'ORD', '', $str ) );
$nextID = 'ORD' . ($id_num+1);
$prevID = 'ORD' . ($id_num-1);

If it doesn’t begin with ORD every time you could replace all non digits

$id_num = intval( preg_replace( '~\D~', '', $str ) );