C++: Cast const reference of Base class to derived class

Question

I am trying to get my Base class instance and cast it to the derived class type. Since I can only get a const reference of my base class instance, I struggle to get it cast correctly. Does anyone have an idea?

class Base
{

};

class Derived : public Base
{

};

Base someBaseInstance;
const Base& GetBase()
{
    return someBaseInstance;
}

int main()
{

    Derived& derived = static_cast<Base&>(GetBase());
    return 0;
}

Answer 1

您必须将您的实例声明为Derived对象。它可以作为Base引用和传递，但必须声明为Derived：

Derived someDerivedInstance;

另外，要在Base和Derived之间进行转换，您应该使用dynamic_cast<>：

Derived &derived = dynamic_cast<Derived&>(GetBase());