c++ - 非标准布局类的布局限制

Question

编译器是否可以自由地对非标准布局类中的数据进行重新排序？比如是否允许改变

struct
{
    char x;
private:
    short y;
public:
    char z;
};

到

struct
{
private:
    short y;
public:
    char x;
    char z;
};

Answer 1

编辑:我最初记错了引用，允许编译器按照 9.2/14 执行此操作:

Nonstatic data members of a (non-union) class with the same access control (Clause 11) are allocated so that later members have higher addresses within a class object. The order of allocation of non-static data members with different access control is unspecified (11). Implementation alignment requirements might cause two adjacent members not to be allocated immediately after each other; so might requirements for space for managing virtual functions (10.3) and virtual base classes (10.1)

它不能做的是用相同的访问说明符重新排序属性。

也就是说，我不知道有任何实现可以随意对属性重新排序，甚至跨访问说明符。