Why is sizeof Derived Class is 8?

Question

#include <iostream>
using namespace std;

class Empty
{};


class Derived : virtual public Empty
{
    char c;
};

int main()
{
    cout << "sizeof(Empty) " << sizeof(Empty) << endl;
    cout << "sizeof(Derived) " << sizeof(Derived) << endl;


    return 0;
}

Why size is coming 8 I think it should be 9, If I declare 'c' as integer then also its coming 8 Cany you please explain me the logic

Answer 1

The size is Implementation dependent and it depends on how the particular compiler implementation implements virtualism & padding. You shouldn't expect the value specifically to be something. If you want to calculate the size in your program just use sizeof and thats about it.

Answer 2

The size is dependent on implementation. Four bytes will be taken for the vtable, one byte is taken for the char, three bytes is for padding. That makes it 8 bytes. So it depends how your compiler is implementing the virtualism and padding. You can use sizeof if you want to calculate the size of your program