What is the underlying data structure of a STL set in C++?

Question

I would like to know how a set is implemented in C++. If I were to implement my own set container without using the STL provided container, what would be the best way to go

Answer 1

Chiming in on this, because I did not see anyone explicitly mention it... The C++ standard does not specify the data structure to use for std::set and std::map. What it does however specify is the run-time complexity of various operations. The requirements on computational complexity for the insert, delete and find operations more-or-less force an implementation to use a balanced tree algorithm.

There are two common algorithms for implementing balanced binary trees: Red-Black and AVL. Of the two, Red-Black is a little bit simpler of an implementation, requiring 1 less bit of storage per tree node (which hardly matters, since you're going to burn a byte on it in a simple implementation anyway), and is a little bit faster than AVL on node deletions (this is due to a more relaxed requirement on the balancing of the tree).

All of this, combined with std::map's requirement that the key & datum are stored in an std::pair force this all upon you without explicitly naming the data structure you must use for the container.

This all, in turn is compounded by the c++14/17 supplemental features to the container that allow splicing of nodes from one tree into another.