Fastest way to get different elements between vectors

[AcarX]

I have 2 vectors which I'd like to retrieve different members as such:

(in_vec1 && not_in_vec2)
(in_vec2 && not_in_vec1)

Performance is a concern so I don't want to iterate through both vectors, twice. Any suggestions?

[JLBorges]

http://en.cppreference.com/w/cpp/algorithm/set_difference

Requires that the elements are ordered. If not, the vectors have to be sorted first ( O( N * log(N) ) ).

[AcarX]

Thanks I'll implement and use that one.