Most efficient way to get next letter in the alphabet using PHP

Given any character from a to z, what is the most efficient way to get the next letter in the alphabet using PHP?

The most efficient way of doing this in my opinion is to just increment the string variable.

$str = 'a';
echo ++$str; // prints 'b'

$str = 'z';
echo ++$str; // prints 'aa' 

As seen incrementing 'z' give 'aa' if you don't want this but instead want to reset to get an 'a' you can simply check the length of the resulting string and if its >1 reset it.

$ch = 'a';
$next_ch = ++$ch; 
if (strlen($next_ch) > 1) { // if you go beyond z or Z reset to a or A
 $next_ch = $next_ch[0];
}

It depends on what you want to do when you hit Z, but you have a few options:

$nextChar = chr(ord($currChar) + 1); // "a" -> "b", "z" -> "{"

You could also make use of PHP's range() function:

$chars = range('a', 'z');  // ['a', 'b', 'c', 'd', ...]

Well, it depends what exactly you want to do with the "edge cases". What result do you expect when the character is z or Z? Do you want the next letter of the same case, or just the next letter, period?

Without knowing the answer to that, for the very basic case, you can just do this:

$next_character = chr(ord($current_character) + 1);

But when you're at Z this will give you [, and z will give you {, according to ASCII values.

Edited as per comment:

If you need the next character of the same case, you can probably just add simple checks after the line above:

if ($next_character == '[')
    $next_character = 'A';
else if ($next_character == '{')
    $next_character = 'a';

These are very simple operations, I really wouldn't worry about efficiency in a case like this.

How about using ord() and chr()?

<?php
    $next = chr(ord($prev)+1);
?>

Since I only care about lowercase characters in this case, I'll use the following code, based on the answers posted here:

function nextLetter(&$str) {
 $str = ('z' === $str ? 'a' : ++$str);
}

Thanks for the help, guys!