```cpp
#include <iostream>

struct A {};
struct B : virtual A {};
struct C {};
struct D : A, C {};
struct E;

int main() {
  std::cout << sizeof(void (A::*)()) << std::endl;
  std::cout << sizeof(void (B::*)()) << std::endl;
  std::cout << sizeof(void (D::*)()) << std::endl;
  std::cout << sizeof(void (E::*)()) << std::endl;
  return 0;
}
```

g++ (GCC) 8.1.1 20180531 64bit

Output:
```
16
16
16
16
```