转换为基类有效性

Question

假设我有一个名为的类Base和一个派生自它的类SuperBase.鉴于add接受a Base*,其中任何一个都是有效的:

SuperBase *super = new SuperBase;
bases.add(super);

要么

SuperBase *super = new SuperBase;
bases.add((Base*)super);

Answer 1

第一个作品只要通过从派生到基础的隐式转换SuperBase公开衍生Base:

struct base { virtual ~base() {} };
struct derived : base {};

base* b = new derived; // okay

第二个也有效,但忽略了对Base以下内容的保护:

struct derived : private base {}; // private base

base* b = new derived; // not okay, base is private
base* b = (base*)(new derived); // okay, but gross

如果是的话private,你可能不应该投它.