PHP关于反斜杠处理函数addslashes()和stripslashes()的用法

<?php
$str = "Who's John Adams?";
echo $str . " This is not safe in a database query.<br />";
echo addslashes($str) . " This is safe in a database query.";
?>

Who's John Adams? This is not safe in a database query.
Who\'s John Adams? This is safe in a database query.

<?php
echo stripslashes("Who\'s John Adams?");
?>

Who's John Adams?