CareerCup

#include <cstdlib>
#include <iostream>

using namespace std;


class Empty
{};
 
class Derived1 : public Empty
{};
 
class Derived2 : virtual public Empty
{};
 
class Derived3 : public Empty
{
    char c;
};
 
class Derived4 : virtual public Empty
{
    char c;
};
 
class Dummy
{
    char c;
};
 

int main(int argc, char *argv[])
{
    cout << "sizeof(Empty) " << sizeof(Empty) << endl;
    cout << "sizeof(Derived1) " << sizeof(Derived1) << endl;
    cout << "sizeof(Derived2) " << sizeof(Derived2) << endl;
    cout << "sizeof(Derived3) " << sizeof(Derived3) << endl;
    cout << "sizeof(Derived4) " << sizeof(Derived4) << endl;
    cout << "sizeof(Dummy) " << sizeof(Dummy) << endl;
    system("PAUSE");
    return EXIT_SUCCESS;
}

and the out put is (In Dev c++)
sizeof(Empty) 1
sizeof(Derived1) 1
sizeof(Derived2) 4
sizeof(Derived3) 1
sizeof(Derived4) 8
sizeof(Dummy) 1

why the size of derived2 is 4 and the size of derived 4 is 8.