addcslashes function and the usage of stripcslashes

The following is a brief introduction to the use of these two functions:

String Addcslashes (String str,string charlist): The 1th parameter, str, is the original string to be lost, and the 2nd parameter charlist describes which characters in the original string need to be preceded by the character "".
String stripcslashes (String str): Removes the "" in the string.

Cases:
<?php
$sql = "Update book set Bookname= ' Let's Go ' where bookid=1";
echo $sql. " <br> ";
$new _sql = addcslashes ($sql, "'");
echo $new _sql. " <br> "; Update book set Bookname= ' Let ' s go ' where bookid=1
$new _sql_01 = stripcslashes ($new _sql);
echo $new _sql_01; Update book set Bookname= ' Let ' s go ' where bookid=1
?>