libboost-container-hash

The Boost.ContainerHash library, part of Boost C++ Libraries, provides boost::hash, an enhanced implementation of the hash function object specified by C++11 as std::hash, and several support facilities (hash_combine, hash_range, hash_unordered_range).

boost::hash supports most standard types and some user-defined types out of the box, and is extensible; it's possible for a user-defined type X to make iself hashable via boost::hash<X> by defining an appropriate overload of the function hash_value.