Turn: Level two pointer

http://www.zhihu.com/question/29186751#answer-13227078

Help yourself to understand the summary:

The first level pointer to the object, you can modify the object's contents through a first level pointer;

Second-level pointer to a first-level pointer, you can modify the content of the first-level pointer through a two-level pointer;

The content of a first-level pointer refers to the address of the object;

The content of a secondary pointer refers to the address of a first-level pointer.

Turn: Level two pointer