Hi, I have a question that I hope can be answered by using Boost. I have the following datastructure: struct ip_info { const u_int8_t _ifile_index; const unsigned long _src_ip; const unsigned long _dst_ip; const u_int16_t _id; const u_int16_t _length; const u_int16_t _src_port; const u_int16_t _dst_port; const u_int32_t _seq; const u_int32_t _ack_seq; }; The object is identified by all its members. Now I want to count duplicates. But I have MANY of these objects, I mean billions. I have to reduce the memory footprint of my program, because it soon grows over 4GB and boom! So I rather not keep all the objects in memory and why would I, because I do not need them. I just need to count duplicates. My idea was to hash such objects to a smaller values and use that hash value as key_type in a map. The value_type of the map would be an integer. This something like std::map<int32_t, u_int16_t> or something. Then I though maybe use Boost.Functional/Hash, but are there any guarantees that the hash value is unique? How unique are they? Are there better alternatives? Thank you, Andrej