为什么我们不能将低+顶级const指针定义为指向int的指针？

Question

1. Define int and pointer to int:

   int i = 22, *p = &i;

2. Define pointer that is low level and top-level const:

   const int *const cp = p;

   (2) is alright - const point with no permission to change the value (of i)

3. Definie a pointer to a pointer that is low+top-level const:

   const int **const cp_2_p = &p;

   (3) isn't alright, why?

   error C2440: 'initializing' : cannot convert from 'int **' to 'const int **const

I'd expect to be able to define a pointer to a pointer to int where I cannot change the address it points to nor the address the pointer it points to, points to.

Answer 1

In general, const applies to the item to its left. The exception of const T is present for historical reasons, and is the conventional alternative to T const .

cp is declared as a constant pointer to a constant int .

cp_2_p is declared as a constant pointer to a non-constant pointer to a constant int.

You would need to declare cp_2_p like this for the types to be compatible:

const int *const *const cp_2_p