A special string ： " the famous �red door� ";
how can i remove the special character : � , that I can get: "the famous re door"

>Solution :

To remove all the characters that do not fall under the above criteria, you have to add ^ after the opening angle bracket so the regular expression to be [^a-zA-Z0-9\s!?.,’"].

Example

<?php
$str = "Hey @there#! How ( are) you *d_oing/?";
echo preg_replace("/[^a-zA-Z0-9\s!?.,\'\"]/", "", $str);