Ultimate Analysis of dynamic_cast and static_cast

Static_cast: cast type conversion. Therefore, it can certainly be used for cast between classes with inheritance relationships. There are three types of subdivisions:
Upcast: Just same as dynamic_cast. Because the runtime type check is not required, the efficiency is higher than that of dynamic_cast;
Downcast: Not safe. It is not recommended.
Crosscast: unavailable. Compilation error.

Dynamic_cast: Cast between classes with inheritance relationships. It is very safe, but it requires a runtime type check and virtual table support, which is less efficient. Category 3:
Upcast: OK. Static_cast is enough.
Downcast: it is required. In this way, the NULL pointer can be obtained only when downcast is incorrect, instead of a non-null pointer that can be used as static_cast.
Crosscast: it can only be used.