Changing class type to a derived class - possible?

[astronemma]

I was wondering if it was possible to change the class of an object to something derived from it, and if so how would be best to do it?

For example, I have an abstract base class called polygon, and derived classes such as triangle, quadrilateral etc, which contain a vector of pairs that are the coordinates of their vertices. I would like to have a class for squares, derived from quadrilateral, but is there a way of changing an object's class from quadrilateral to square (after checking that the quadrilateral is a square of course)?

I've been reading here (http://www.cplusplus.com/doc/tutorial/typecasting/) about static_cast but I can't really get my head around it. Does this only work in the case of pointers?

Thanks!

[Zhuge]

You may want to look into dynamic_cast<>(). However, what you are trying to do suggests a design flaw; if you are putting all these polygons into a list, you should treat them as polygons. If you want to handle them in special ways based on their actual type either use polymorphism or actually handle them separately.

[astronemma]

Ahh yes, sorry if I wan't clear before, I am using polymorphism already. I'll look into dynamic_cast, thanks.

[Zhuge]

If you need to cast to a more specific type, you aren't using polymorphism anymore. If you were using polymorphism, you would call a method on polygon that was overridden to do the proper thing for whatever type you were actually working with.