C++：class 类型的 const 是否始终是顶级 const？

Question

Here are the following code:

#include <iostream>
using namespace std;

class A {
public:
   int *x;
};

int main() {
   int b=100;
   A a;
   a.x = &b;
   const A &m = a; // clause 1 - Is this top-level const? 
   int *r = m.x; // *r has no const yet allowed. Is it due to reference m being top level const?
}

Any help appreciated.
Thanks

Answer 1

int const ca = 24;
int a = ca;

You would expect this to compile right? And indeed it does. Here I initialized a integer with the value 24 .

You code is the same situation, except that instead of integer you have pointer to integer:

m is const so mx is const. The x is const, ie x cannot be modified (via m ). In stricter terms mx is of type int * const ie constant pointer to integer.

int *r = m.x

Here you just initialize the pointer r with the value of the pointer mx . The fact that mx is const is not an issue. Both types without their top level cv are identical: pointer to (mutable) integer.

---

const A &m = a; // clause 1 - Is this top-level const?

Yes