C++ 从基类指针访问派生类成员 [英] C++ Access derived class member from base class pointer

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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