关于无名结构体的见解

struct T1 {
    char a;
    char b;
    struct  {
        char a;
    };
};

struct T1 {
    char a;
    char b;
    struct T2 {
        char a;
    };
};

struct T3 {
    char a;
    char b;
    struct {
        char a;
    } T4;
};

struct T5 {
    char a;
    char b;
    struct T6 {
        char a;
    } T6;
};