What are the potential pitfalls of using functions like strtoupper/lower to manipulate strings containing special characters in PHP?

Using functions like strtoupper() or strtolower() to manipulate strings containing special characters can lead to unexpected results or data corruption. This is because these functions do not take into account the encoding of the string, which can result in incorrect transformations of special characters. To properly handle strings with special characters, it is recommended to use multibyte string functions like mb_strtoupper() and mb_strtolower(), which support different character encodings.

// Using mb_strtoupper() to handle strings with special characters
$string = "Café";
$uppercasedString = mb_strtoupper($string, 'UTF-8');
echo $uppercasedString;