Question

didnot need to do与 neednot have done 的区别

Answer 1

didn‘t need to do里need是普通动词,就是need本来的意思,（过去）没必要/不需要做某事

need not have done 里need是情态动词,意思是本来无必要做某事（却做了）,本不该做某事

例如：

He did not need to come early,so he came late.

他不需要早来,所以他来得晚.

He needn't have come early,but he did and waited one hour.

他不需要早来却早来了,还等了一个小时.