const pointers vs const references in C++

Question

According to the following program, I can understand that, const keyword at a front of a references means Const Reference to const value, correct?

#include <iostream>
using namespace std;

struct s
{
    int x;
};

int main(void)
{
    s a = {10}, b = {30};

    // IN POINTERS ----------------
    const s* ptrToConstValue;
    ptrToConstValue= &a;
    //ptrToConstValue->x = 30; 
    ptrToConstValue = &b;

    s* const constPtrToNonConstVaue = &a;
    constPtrToNonConstVaue->x = 40;
    //constPtrToNonConstVaue = &b;

    const s* const constPtrToConstValue = &a;
    //constPtrToConstValue = &b;
    //constPtrToConstValue->x = 30;


    // IN REFERENCES -------------
    const s& seemsToBeConstRefToConstValue = a;
    //s = b;
    //s.x = 30;

    return 0;
}

Answer 1

So the confusion is this:

X x;

X* px       = &x; // pointer to x
X* const px  = &x; // *const pointer* to x

const X* px   = &x; // pointer to *const x*
X const* px   = &x; // identical

const X* const px = &x; // *const pointer* to *const x*

Now in reference, the 'pointer part' is always const:

X& rx = x;       // ref to x

X const& rx = x; // ref to const x
const X& rx = x; // identical

Answer 2

References are always const, so you don't need the const keyword for them; it is, in fact, forbidden.

So you have:

S*                ps;   //  Non-const pointer to a non-const value
S const*          psc;  //  Non-const pointer to a const value
S* const          pcs;  //  Const pointer to a non-const value
S const* const    pcsc; //  Const pointer to a const value

, but only:

S&                rs;   //  (const) reference to a non-const value
S const&          rsc;  //  (const) reference to a const value

The const which immediately follows the name of the type can be moved to the beginning of the declaration, at the cost of some confusion to the reader.