Why pointers to the same object have different values? [duplicate]

Question

I've this piece of code:

#include <iostream>

class A
{
public:
    A() : m_i(0) { }
protected:
    int m_i;
};
class B
{
public:
    B() : m_d(0.0) { }
protected:
    double m_d;
};
class C : public A, public B
{
public:
    C() : m_c('a') { }
private:
    char m_c;
};

int main()
{
    C d;
    A *b1 = &d;
    B *b2 = &d;

    std::cout << (long)b1 << std::endl <<(long)b2<< std::endl;
}

when compiled and run it produces the following output:

140734705182320
140734705182328

It is not completely clear why different pointers to the same address (&d) have different values.

thanks in advance.

Answer 1

The memory layout of a C object will be something like:

A base_object_1;
B base_object_2;
char m_c;

The two base objects have different addresses; A will (typically) have the same address as the full object, but B will (typically) not. Certainly they can't have the same address as each other, unless at least one is empty.

So converting a pointer to the full object into a pointer to one of the base objects must change the pointer value in order to point to the correct address.