class CallbackClass {     function CallbackFunction() {         // refers to $this     }       function static StaticFunction() {         // doesn't refer to $this     }  }    function NonClassFunction($errno, $errstr, $errfile, $errline) {  }    // 三种方法如下:    1: set_error_handler('NonClassFunction');  // 直接转到一个普通的函数 NonClassFunction    2: set_error_handler(array('CallbackClass', 'StaticFunction')); // 转到 CallbackClass 类下的静方法 StaticFunction    3: $o =& new CallbackClass();      set_error_handler(array($o, 'CallbackFunction'));  // 转到类的构造函数，其实本质上跟下面的第四条一样。    4. $o = new CallbackClass();      // The following may also prove useful:    class CallbackClass {     function CallbackClass() {         set_error_handler(array(&$this, 'CallbackFunction')); // the & is important     }          function CallbackFunction() {         // refers to $this     }  }