How does the PHP function htmlentities() differ from htmlspecialchars() and when should each be used?

The PHP function htmlentities() is used to convert characters to HTML entities, while htmlspecialchars() is used to convert special characters to HTML entities. The main difference between the two is that htmlentities() converts all characters to HTML entities, including characters that are already HTML entities, while htmlspecialchars() only converts characters that have special meaning in HTML. If you need to encode all characters, including those that are already HTML entities, you should use htmlentities(). If you only need to encode characters with special meaning in HTML, then htmlspecialchars() is the appropriate choice.

// Using htmlentities() to encode all characters to HTML entities
$encoded_string = htmlentities($string);

// Using htmlspecialchars() to encode only special characters to HTML entities
$encoded_string = htmlspecialchars($string);