PHP 2 chars decrement (AB -> AA) [duplicate] - php

Question

This question already has answers here:
Increment letters like number by certain value in php
(2 answers)
Closed 4 years ago.
I am implementing some export functions using PHPExcel.
Since PHP can increment alphabet automatically it had been working fine but I have an issue when trying to decrement it.
I can decrement a single character like this $decremented = chr(ord($someChar) - 1);, but it does not work on 2 characters (such as 'AA','BB', .. etc.)
Is there any way that I can decrement two characters? Like 'ZZ' -> 'ZX', 'AA'->'Z'
Any help or thoughts would be really appreciated!

Answer 1

Here's a decrement function that will work for you:
function decrement($str) {
$index = strlen($str)-1;
$ord = ord($str[$index]);
if ($ord > 65) {
// The final character is still greater than A, decrement
return substr($str, 0, $index) . chr($ord-1);
}
if ($index > 0) {
// Strip the final 2 characters and append a Z
return substr($str, 0, $index-1) . 'Z';
}
// Can't be decremented
return false;
}
https://3v4l.org/WaaKY

Answer 2

Somebody wrote a function for this here.
function decrementLetter($char) {
$len = strlen($char);
// last character is A or a
if(ord($char[$len - 1]) === 65 || ord($char[$len - 1]) === 97){
if($len === 1){ // one character left
return null;
}
else{ // 'ABA'--; => 'AAZ'; recursive call
$char = decrementLetter(substr($char, 0, -1)).'Z';
}
}
else{
$char[$len - 1] = chr(ord($char[$len - 1]) - 1);
}
return $char;
}