What is the difference between substr() and mb_substr() in PHP, and when should each be used?

The main difference between substr() and mb_substr() in PHP is that substr() operates on bytes, while mb_substr() operates on characters. If your string contains multibyte characters (e.g., UTF-8), you should use mb_substr() to ensure correct character handling. If your string contains only single-byte characters, you can use substr() without issues.

// Using substr() to extract a substring from a string with single-byte characters
$string = "Hello, World!";
$substring = substr($string, 0, 5);
echo $substring;

// Using mb_substr() to extract a substring from a string with multibyte characters (e.g., UTF-8)
$string = "こんにちは、世界！";
$substring = mb_substr($string, 0, 5, 'UTF-8');
echo $substring;