What is the difference between std::map and std::unordered_map?

Question

Accepted Answer

**std::map:** - Red-black tree (ordered) - O(log n) lookup - Keys must be comparable - Iteration in sorted order ```cpp std::map m; m[3] = "three"; m[1] = "one"; // Iteration: 1, 3 (sorted) ``` **std::unordered_map:** - Hash table (unordered) - O(1) average lookup - Keys must be hashable - No order guarantee ```cpp std::unordered_map um; um[3] = "three"; um[1] = "one"; // Iteration order: unknown ``` **When to use:** - `map`: ordered iteration, range queries - `unordered_map`: fast lookup, no ordering needed

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