C++11: Map vs Unordered Map Performance

What are the main differences in performance between std::map and std::unordered_map in C++11?

The main differences lie in their underlying data structures. std::map is implemented as a balanced tree, which provides O(log n) complexity for insertions, deletions, and lookups. In contrast, std::unordered_map uses a hash table, offering average O(1) complexity for these operations, but can degrade to O(n) in the worst case.

When should I use std::map instead of std::unordered_map?

You should use std::map when you need ordered keys, as it maintains the order of elements. It's also useful when you need to perform range queries or when you require a sorted iteration.

Are there any memory usage differences between the two?

Yes, std::map generally uses more memory due to the overhead of maintaining the tree structure. std::unordered_map may use less memory for the actual data but can have additional overhead for the hash table's buckets.

Can you give an example of when unordered_map would be faster?

Certainly! If you're frequently inserting and looking up elements without needing order, std::unordered_map will typically be faster due to its average O(1) complexity for these operations.