had加过去分词是谓语动词过去完成时的形式；had加过去分词是指过去某一动作之前已经发生或完成的动作，即动作有先后关系，动作在前的用过去完成时，在后的用一般过去时。

She'll have had the results by now.

她现在应该知道结果了。

We had a day out in the country.

我们在乡下玩了一天。

He had to go to the hospital for treatment.

他不得不去医院接受治疗。