What is the difference between std::map and std::unordered_map containers in C++?

Main differences between std::map and std::unordered_map in C++:

• Data structure:

  • std::map is implemented as a balanced tree (usually a red-black tree).
  • std::unordered_map is implemented based on a hash table.

• Order of elements:

  • std::map stores elements in sorted order by key.
  • std::unordered_map does not guarantee the order of elements.

• Operation complexity:

  • Insertion, search, and deletion in std::map are O(log n).
  • In std::unordered_map, on average O(1), but in the worst case O(n).

• Key requirements:

  • std::map requires the < operator for key comparison.
  • std::unordered_map requires a hash function and the == operator.

The choice depends on the need for ordering and performance requirements.