Use of `const` when declaring a parameter of a pointer type in C [duplicate]

Is such a declaration legal?

Yes, although the effect isn't the same as if const precedes p's type.

Also, what is the difference between the following:

1. void f(const int *p)

   Putting const before p's type protects the object that p points to.

   Example:

   void f(const int *p) {
      int j;
   
      *p = 0;       //WRONG
      p = &j;       //legal
   }
   

2. void f(int * const p)

   Putting const after p's type protectsp itself.

   Example:

   void f(int * const p) {
      int j;
   
      *p = 0;       //legal
      p = &j;       //WRONG
   }
   

   This feature isn't used very after since p is merely a copy of another pointer, there's rarely any reason to protect it. An even greater rarity is the next case.

3. void f(const int * const p)

   Here const is protecting both p and the object it points to.

   Example:

   void f(const int * const p) {
      int j;
   
      *p = 0;       //WRONG
      p = &j;       //WRONG
   }
   

4. void f(int const *p)

   This is the same as void f(const int *p). See point 1.