当扩展填充结构时，为什么不能在尾填充中放置额外的字段?

Let's consider the structs :

让我们考虑结构:

struct S1 {
    int a;
    char b;
};

struct S2 {
    struct S1 s;       /* struct needed to make this compile as C without typedef */
    char c;
};

// For the C++ fans
struct S3 : S1 {
    char c;
};
struc