const ptr與ptr const比較

其實只要注意從右向左讀取，這樣就很好識別了

可以參考下這關於const的faq

舉個例子 const * int p 有些時候會忽悠進int const * 和 int *const之類的當中來迷惑

You have to read pointer declarations right-to-left.

• Fred const* p means "p points to a constant Fred": the Fred object can't be changed via p.
• Fred* const p means "p is a const pointer to a Fred":
  you can't change the pointer p, but you can change the Fred object via p.
• Fred const* const p means "p is a constant pointer to a constant Fred": you can't change the pointer p itself,
  nor can you change the Fred object via p.