指针*，引用&，解引用*，取地址&
&可以作为取地址用。&a返回取a的地址，a是一个对象。&映射对象到地址。
In this case, & can be called Address of operator.
*可以作为解引用操作符。*p返回p所指向的对象，p是一个地址。*映射地址到对象。
In this case, * can be called Indirection operator. Indirection operator returns the value
of the variable located at the address specified by its operand.
Indirection operator * is the complement of Address of operator &.
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