问题描述
例如，我有一些类层次结构（可能，有各种继承 - public，private，public virtual，multi-inheritance等）：
For example, I have some class hierarchy (possibly, with all kinds of inheritance - public, private, public virtual, multi-inheritance, etc.):
class A {
int a;
public:
virtual ~A() {}
};
class B: public A { int b; };
class C: public virtual B { int c; };
class E: public virtual B { int e; };
class F: public C, public E { int f; };
使用casts获取指向主big对象的每个子对象的指针：
Using casts I get pointers to every sub-object of the main "big" object:
F * f = new F;
E * e = f;
C * c = f;
B * b = f;
A * a = f;
我可以比较这些指针对的相等性（operator ==），为什么？
比较是否使用delta逻辑或其他技术？
What pairs of these pointers may I compare for equality (operator==) and why?Will the comparison use delta-logic or some other technique?
当我不能比较指向同一个复杂对象的指针时，有什么可能的情况？
它可以是什么类型的对象？
What are the possible situations, when I can't compare pointers to the same complex object?What kind of object it can be?
我希望所有指向同一对象的指针总是相等的。
I expect, that all of the pointers to the same object are always equal.
推荐答案
如果一个指针类型可以隐式转换为另一个指针，则可以比较两个指针;也就是说，如果它们都指向同一类型，或者一个指向另一个的基类。转换将对地址进行必要的调整，以便如果两个指针指向同一个对象，它们将比较相等。
You can compare two pointers if one pointer type is implicitly convertible to the other; that is, if they both point to the same type, or one points to a base class of the other's. The conversion will make the necessary adjustment to the address so that, if both pointers point to the same object, they will compare equal.
在这种情况下，对 c == e ，因为 C 和 E 是从另一个派生的。要比较这些，你需要交叉转换，或将两者转换为它们的共同基类;
In this case, you can compare any pair except c == e, since neither of C nor E is derived from the other. To compare those, you would either need to cross-cast, or to convert both to their common base class; neither of these can be done implicitly.
顺便说一下，您的代码中不需要 dynamic_cast ，因为你正在转换为基类指针，并且可以隐式完成安全转换。
By the way, there's no need for dynamic_cast in your code, since you're casting to base class pointers and that safe conversion can be done implicitly.
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