Question

Actually I need a data structure that helps me in reducing time for look-ups and retrieval of values of the respective keys.

Right now I am using a map container with key as structure and want to retrieve its values as fast as possible.

I am using gcc on fedora 12. I tried unordered map also, but it is not working with my compiler.

Also, Hash map is not available in namespace std.

Answer 1

If you’re using C++11, use std::unordered_map, defined in <unordered_map>.

Otherwise, use std::tr1::unordered_map, defined in <tr1/unordered_map>, or boost::unordered_map, defined in <boost/unordered_map.hpp>.

If your key is a user-defined type, then you’ll need to either define hash and operator== for the type, or provide suitable function types as template arguments to unordered_map.

Of course, you should also measure the performance compared to std::map; that may be faster in some circumstances.