c – 为什么static_cast为同一个对象提供不同的内存位置？

class Parent { int a; };
class Child { int b; };
struct GrandChild : public Parent,public Child { int a,b,c; };

int main() {
    GrandChild Gc;
    std::cout << "GrandChild's address is at : " <<&GC<<endl;
    std::cout << "Child's address is at : " <<static_cast<Child*>(&GC)<<endl;
    std::cout << "Parent's address is at : " <<static_cast<Parent*>(&GC)<<endl;

}

输出：

GrandChild's address is at : 0077F6F8
Child's address is at : 0077F6FC
Parent's address is at : 0077F6F8

为什么在static_cast之后内存位置有如上所述的不一致？