c++: volatile member function in volatile instance - assigning array to pointer is invalid conversion?

Question

Consider the following example:

#include <iostream>

class C {
    int intArray[2] { 1, 2 };
    int *firstElementPt;

    public:
        int getFirstElement() volatile {
            firstElementPt = intArray;
            return *firstElementPt;
        };
};

int main()
{
    volatile C c;
    std::cout << c.getFirstElement();
}

This gives me the following compilation error:

 In member function 'int C::getFirstElement() volatile':
10:28: error: invalid conversion from 'volatile int*' to 'int*' [-fpermissive]

I'm new to C++. I read that declaring an instance as volatile would implicitly make all it's member variables volatile. And I read that declaring a member function as volatile would mean to mark the hidden *thispointer as volatile. So why is the assignment firstElementPt = intArray; still not allowed and leads to error: invalid conversion from 'volatile int*' to 'int*'?

Answer 1

Volatility and constness do not propagate through pointers, but they do propagate through arrays. So in a volatile instance of the class, firstElementPt is itself volatile, but the thing it points to is not. The intArray elements however are volatile. You are attempting to point a volatile-pointer-to-a-non-volatile-int to a volatile int. This is not allowed.