Set_include_path and get_include_path usage and precautions

Set_include_path: sets the default include path. This article describes how to use it and its precautions. if you are interested, you can understand it. it may be helpful for you to learn about php. set_include_path: sets the default include path.
Find the include or require file in the default include path and then in the same directory
Example:
D:/xampp/htdocs/test/include has a file named cls. mysqli. php.
D:/xampp/htdocs/test/has a file named set_include_path.php.
The content is
The code is as follows:
Set_include_path ('/xampp/htdocs/test/include'); // note that '/' in php indicates not the root directory of the website, but the drive letter of the file, available echo realpath ('/'); view
// If the php version is too low, this function is not supported and can be used in the general version of ini_set ()
/* View the actual default include path */
Echo realpath (get_include_path ());
/* To include cls. mysqli. php, you only need */
Require_once ('cls. mysqli. php ');
$ Mysql = new Mysql ('localhost', 'root', '', 'test'); // The instantiated and subsequent query statements are correct.