Use __autoload() in php to automatically load undefined classes

/**
* Automatically load related class library files
*/
function __autoload($classname){
if(substr($classname,-6)=="Action"){
include APP_PATH.'controllers /'.$classname.'.class.php';
}elseif(substr($classname, -5)=="Model"){
include APP_PATH.'models/'.$classname.'.class.php' ;
}elseif($classname=="Smarty"){
include SYSTEM_PATH.'smarty/Smarty.class.php';
}else{
include APP_PATH.'common/'.$classname.'.class.php' ;
}
}
?>

Another way to include the path:

function __autoload($class_name) {
$path = str_replace('_', DIRECTORY_SEPARATOR, $class_name);
require_once $path.'.php';
}
?>

Instructions: Convert the underscore to the directory separator (DIRECTORY_SEPARATOR). This can effectively manage library files and solve cross-platform problems.