第11月第21天 php引用

1.

class CI_Controller {

    private static $instance;

    /**
     * Constructor
     */
    public function __construct()
    {
        self::$instance =& $this;

        // Assign all the class objects that were instantiated by the
        // bootstrap file (CodeIgniter.php) to local class variables
        // so that CI can run as one big super object.
        foreach (is_loaded() as $var => $class)
        {
            $this->$var =& load_class($class);
        }

        $this->load =& load_class(‘Loader‘, ‘core‘);

        $this->load->initialize();

        log_message(‘debug‘, "Controller Class Initialized");
    }

    public static function &get_instance()
    {
        return self::$instance;
    }
}

...

public function database($params = ‘‘, $return = FALSE, $active_record = NULL)
    {
        // Grab the super object
        $CI =& get_instance();

        // Do we even need to load the database class?
        if (class_exists(‘CI_DB‘) AND $return == FALSE AND $active_record == NULL AND isset($CI->db) AND is_object($CI->db))
        {
            return FALSE;
        }

        require_once(BASEPATH.‘database/DB.php‘);

        if ($return === TRUE)
        {
            return DB($params, $active_record);
        }

        // Initialize the db variable.  Needed to prevent
        // reference errors with some configurations
        $CI->db = ‘‘;

        // Load the DB class
        $CI->db =& DB($params, $active_record);
    }

$a=test()方式调用函数，只是将函数的值赋给$a而已，　而$a做任何改变　都不会影响到函数中的$b
而通过$a=&test()方式调用函数呢, 他的作用是　将return $b中的　$b变量的内存地址与$a变量的内存地址　指向了同一个地方
即产生了相当于这样的效果($a=&$b;) 所以改变$a的值　也同时改变了$b的值　所以在执行了
$a=&test();
$a=5;
以后，$b的值变为了5

http://www.cnblogs.com/xiaochaohuashengmi/archive/2011/09/10/2173092.html