title: set map implementation in C++
body: <p>I find that both set and map are implemented as a tree. set is a binary search tree, map is a self-balancing binary search tree, such as red-black tree? I am confused about the difference about the implementation. The difference I can image are as follow</p>
  
  <p>1) element in set has only one value(key), element in map has two values.
  2) set is used to store and fetch elements by itself. map is used to store and fetch elements via key.</p>
  
  <p>What else are important?</p>