How can I increase the performance in a map lookup with key type std::string?

Question

I\'m using a std::map (VC++ implementation) and it\'s a little slow for lookups via the map\'s find method.

The key type is std::string.

Answer 1

Depending on the usage cases, there are some other techniques you can use. For example we had an application that needed to keep up with over a million different file paths. The problem with that there were thousands of objects that needed to keep small maps of these file paths.

Since adding new file paths to the data set was an infrequent operation, when path was added to the system, a master map was searched. If the path was not found, then it was added and a new sequenced integer (starting at 1) was returned. If the path already existed, then the previously assigned integer was returned. Then each map maintained by each object was converted from a string based map to an integer map. Not only did this greatly improve performance, it reduced memory usage by not having so many duplicate copies of the strings.

Sure, this is a very specific optimization. But when it comes to performance improvements, you often find yourself having to make tailored solutions to specific problems.

And I hate strings :) Not are they slow to compare, but they can really trash your CPU caches on high performance software.