问题描述
如果我分配一个 Derived 类的对象(具有 Base 的基类)，并将指向该对象的指针存储在指向基类的变量中类，如何访问 Derived 类的成员?
If I allocate an object of a class Derived (with a base class of Base), and store a pointer to that object in a variable that points to the base class, how can I access the members of the Derived class?
这是一个例子:
class Base
{
public:
int base_int;
};
class Derived : public Base
{
public:
int derived_int;
};
Base* basepointer = new Derived();
basepointer-> //Access derived_int here, is it possible? If so, then how?
推荐答案
不，您不能访问 derived_int 因为 derived_int 是 Derived 的一部分，而 basepointer 是指向 Base 的指针.
No, you cannot access derived_int because derived_int is part of Derived, while basepointer is a pointer to Base.
你可以反过来做:
Derived* derivedpointer = new Derived;
derivedpointer->base_int; // You can access this just fine
派生类继承基类的成员，而不是相反.
Derived classes inherit the members of the base class, not the other way around.
但是，如果您的 basepointer 指向 Derived 的实例，那么您可以通过强制转换访问它:
However, if your basepointer was pointing to an instance of Derived then you could access it through a cast:
Base* basepointer = new Derived;
static_cast<Derived*>(basepointer)->derived_int; // Can now access, because we have a derived pointer
请注意，您需要先将继承更改为 public:
Note that you'll need to change your inheritance to public first:
class Derived : public Base
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