Sorting Sets using std::sort

Question

I would like to know if we can sort a pre created set. When I first create the set s_p2, I sort using a different element point.getLength(). but after user input i would like to sort the items according to the x value point.getX(). How i do this ?

It seems like set container does not have a sort function. And i am advised to use vector. But sets are able to store unique elements only.

Q1: How can i sort a set depending on the criteria

Q2: If set is unable to do this than which STL container is the best choice and how can i sort the elements in the container.

Answer 1

You cannot resort a set, how it sorts is part of the type of the particular set. A given set has a fixed set order that cannot be changed.

You could create a new set with the same data relatively easily. Just create a new set that sorts based on the new criteria.

If you want to use the two sets in the same code, you'll have to abstract the access to the underlying set.

Now, if you are doing rare reads and modifications, using a vector that you sort manually is often a better idea. You can remove duplicates by using the std::unique-erase idiom.

Answer 2

std::set stores its members in a sorted fashion. If you walk through the set from .begin() to .end(), you will have a sorted list of items.

If you don't like the default sort criteria, you may supply a 2nd template parameter to std::set<>