Examples of set_include_path and get_include_path in php

set_include_path('/xampp/htdocs/test/include'); //Please note that the '/' in php does not represent the root directory of the website, but the drive letter where the file is located, available echo realpath('/'); View
//If the PHP version is too low, this function is not supported, you can use the general version ini_set()
/*View the real default include path*/
echo realpath(get_include_path());
/*To include cls.mysqli.php just need to*/
require_once('cls.mysqli.php');
$mysql = new Mysql('localhost','root','' ,'test'); //There are no errors in instantiation and subsequent query statements