derive layout

https://www.cnblogs.com/pandamohist/p/13882020.html

#include "iostream"
struct B {
    virtual void f() {}
    uint64_t b;
};

struct C {
    virtual void fc() {}
    uint64_t c;
};

struct D : public B, public C{
    virtual void fd() {}
    uint64_t d;
};


int main(){
    D d;
    printf("%llx\t%llx\t%llx\t%llx\n", &d, &d.b, &d.c, &d.d);
    std::cout << sizeof( B) <<'\t'  << sizeof( C) <<'\t' << sizeof( D) <<'\n';
    return 0;
}