I'm using C++11 and the std::hash algorithm. I was wondering, what actual hash implementation is used? I would assume MD5 or SHA, but I can't dig any info from the internets.
Also, I'd like to know the actual returned bit-width of the hash, as I have to store it in MySQL.
Finally, is it preferable to use std::hash, over say some other library such as crypto++ ?
The algorithm chosen for std::hash is solely implementation dependant. Probably neither MD5 or SHA are used since they would be performance killers for its purpose.
Most implementation will be much more trivial than the above mentioned since there is no cryptographic requirement for std::hash while MD5 and SHA have been developed for cryptographic purposes.
The requirements of std::hash are much less strict:
Key.size_t that represents the hash value of the parameter.k1 and k2 that are equal, std::hash<Key>()(k1) == std::hash<Key>()(k2).k1 and k2 that are not equal, the probability that std::hash<Key>()(k1) == std::hash<Key>()(k2) should be very small, approaching 1.0/std::numeric_limits<size_t>::max().
std::hash nothing has to do with cryptographic security. Its implementation is mostly used with associative unordered containers like map. The implementation doesn't care about cryptographic, it cares about efficiency when used to manage hash tables. If you need cryptographic security then you should really point toward an external library meant to be used for that purpose.
boost::uuid.