A recent talk about unordered_map
in C++ made me realize that I should use unordered_map
for most cases where I used map
before, because of the efficiency of lookup ( amortized O(1) vs. O(log n) ). Most times I use a map, I use either int
or std::string
as the key type; hence, I've got no problems with the definition of the hash function. The more I thought about it, the more I came to realize that I can't find any reason of using a std::map
over a std::unordered_map
in the case of keys with simple types -- I took a look at the interfaces, and didn't find any significant differences that would impact my code.
Hence the question: is there any real reason to use std::map
over std::unordered_map
in the case of simple types like int
and std::string
?
I'm asking from a strictly programming point of view -- I know that it's not fully considered standard, and that it may pose problems with porting.
Also, I expect that one of the correct answers might be "it's more efficient for smaller sets of data" because of a smaller overhead (is that true?) -- hence I'd like to restrict the question to cases where the amount of keys is non-trivial (>1 024).
Edit: duh, I forgot the obvious (thanks GMan!) -- yes, maps are ordered of course -- I know that, and am looking for other reasons.