Why cast Super-class objects to derived-class objects?

Question

Whats the purpose of doing this👇
Creating two classes and extending the 1st with the second,what's the purpose of downcasting a super object to a sub class object,does anything change when i try to use that sub class object..
I.e......
Super* super_obj;
Sub* sub_obj=dynamic_cast<*super_obj>();
...........

Answer 1

You may need to do this if the pointer to the Super class was actually holding an object of the Sub class. You can then safely move it to a Sub class pointer using dynamic_cast. In case the conversion fails, you get a nullptr in sub_obj.

Secondly your cast is a bit doubtful. I think what you intended was:

Sub* sub_obj = dynamic_cast<Sub*>(super_obj);

In your code above, the parenthesis were empty, and the cast must be to the type you are going to store the variable in. (otherwise why cast in the first place?)