什么是空指针常量（null pointer constant）?[6.3.2.3-3] An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant.这里告诉我们：0、0L、’\0’、3 – 3、0 * 17 （它们都是“integer constant expression”）以及 (void*)0 （ty
参考链接：
https://blog.csdn.net/youyou519/article/details/82704401
https://blog.csdn.net/qq_40334837/article/details/96297079
https://blog.csdn.net/ChaoFeiLi/article/details/103612849
倒着读：
char * const s
s is a const pointer to char，翻译：s是一个常量指针（所以s的指向是固
