What is the difference between htmlspecialchars and htmlentities in PHP and when should each be used?

The main difference between htmlspecialchars and htmlentities in PHP is that htmlspecialchars only converts predefined characters (<, >, ", ', &) to their HTML entities, while htmlentities converts all applicable characters to their HTML entities. htmlspecialchars should be used when you only want to encode the predefined characters for use in HTML, such as when displaying user input on a webpage. htmlentities should be used when you want to encode all applicable characters, which is useful when dealing with different character encodings.

// Using htmlspecialchars to encode predefined characters
$encodedString = htmlspecialchars($inputString);

// Using htmlentities to encode all applicable characters
$encodedString = htmlentities($inputString);