c++ - 析构函数中的动态转换

Question

这个代码合法吗？

class Base1 {
};

class Base2 {
public:
    virtual ~Base2() {
        if (!dynamic_cast<Base1*>(this))
            std::cout << "aaaa" << std::endl;
    }
    Base2() {
    }
};

class MyClass: public Base1, public Base2 {
public:
    MyClass() {
    }
    virtual ~MyClass() {
        std::cout << "bbb" << std::endl;
    }
};

int main() {
    MyClass s;
    return 0;
}

我看到了两张照片，但我应该只看到一张。我猜动态 Actor 是错误的。可以做这种检查吗？

Answer 1

也许我自己找到了解决方案，答案是否定的，这是不可能的:

来自 bullet 6 of cppreference.com documentation :

When dynamic_cast is used in a constructor or a destructor (directly or indirectly), and expression refers to the object that's currently under construction/destruction, the object is considered to be the most derived object. If new-type is not a pointer or reference to the constructor's/destructor's own class or one of its bases, the behavior is undefined.

另请参阅标准的 [class.cdtor]/6。

由于我在 Base2 析构函数中强制转换为 Base1，因此此行为未定义。