The `addslashes()` string function in PHP 8.4 is used to escape certain characters in a string by adding backslashes before them. The characters that are escaped include single quotes (`’`), double quotes (`”`), backslashes (`\`), and NULL bytes. This function is particularly useful when preparing strings for storage in databases or for evaluation by `eval()`.

Syntax:

<?php
addslashes(string $string): string
?>

Example:

<?php
$str = "Is your name O'Reilly?";
$escaped_str = addslashes($str);
echo $escaped_str; // Outputs: Is your name O\'Reilly?
?>

In this example, the single quote in “O’Reilly” is escaped with a backslash.