C++ map insertion and lookup performance and storage overhead

Question

I would like to store a mapping of an integer key to a float value in-memory.

I have roughly 130 million keys (and, accordingly, 130 million v

Answer 1

If your input is sorted, you should try just a vector and a binary search (i.e., lower_bound()). This might prove adaquate (it is also O(log n)). Depending on the distribution of your keys and the hash function used, a hash_map might work as well. I think this is tr1::unordered_map in gcc.