c++ - 如果类包含基类的成员，编译器能否利用空基优化？

Question

考虑

struct base {};
struct child : base {};

众所周知，通过应用空基优化，sizeof(child) 可以为 1。

但是，现在考虑一下

struct base {};
struct child : base {base b;};

编译器现在可以应用空基优化，还是 sizeof(child) 必须至少为 2？

引用:http://en.cppreference.com/w/cpp/language/ebo

Answer 1

不，它不能。来自同一引用:

Empty base optimization is prohibited if one of the empty base classes is also the type or the base of the type of the first non-static data member

因此 sizeof(child) >= 2。