C++从基类指针访问派生类成员

Question

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？

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?

Answer 1

不，您不能访问 derived_int 因为 derived_int 是 Derived 的一部分，而 basepointer 是指向基础.

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。

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:

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:

class Derived : public Base