how to access an array declared in sketch from library c++

I'm making a library to do some OOP, that depends on another library also.. just getting used to c++, but my question is..

Simply put, what would be a way I access an array in my new library that is declared in the sketch that uses the other library?

Probably by a pointer. But, it would help to post a concrete example of what you're talking about.

Will post an example if this way doesn't work, I now think i need to make the array within the new library instead of the sketch. will try a few things first. Sorry, my question was not very coherent. Thanks