What is the difference between using std::map and std::unordered_map in C++, and what are their main differences?

std::map and std::unordered_map are containers for storing key-value pairs in C++, but they have important differences:

• std::map:

  • Based on a balanced tree (usually a red-black tree).
  • Keys are stored in sorted order.
  • Search, insert, and delete operations have a complexity of O(log n).
  • Supports ordered traversal of elements.

• std::unordered_map:

  • Based on a hash table.
  • Keys are not ordered.
  • Search, insert, and delete operations have an average complexity of O(1), but can be O(n) in the worst case.
  • Faster for large data volumes if order is not important.

The choice between them depends on the requirements for element order and performance. If a sorted container is needed — use std::map. If access speed is important and order is not — std::unordered_map.