请让我理解将派生类对象分配给基类指针-C ++

Question

Lets say you have a base class Base and derived class Derived .

Base b;
Derived *d;
d=&b; // this line gives error, why? I think it asks for typecasting, why?
//When you assign derived class object address to base class pointer, it works fine. Why not the above case works fine

While below code works,

Derived *d=new Base(); //no typecasting required here, why?

What's the difference between above two cases?

Thanks!

Answer 1

Base is-not-a Derived , so neither this:

Base b;
Derived *d;
d=&b; 

nor this:

Derived* d = new Base();

makes any sense or works. Both would result in something like

error: invalid conversion from 'Base*' to 'Derived*' [-fpermissive]

Both are doing exactly the same thing: assigning a Base* to a Derived* .