Can set_intersection be used with hash_set in C++?

Question

I am calculating intersection, union and differences of sets. I have a typedef of my set type:

typedef set node_set;

When it i

Answer 1

I don't think so.

One of the pre-condition of set_intersection is:

• [first1, last1) is ordered in ascending order according to operator<. That is, for every pair of iterators i and j in [first1, last1) such that i precedes j, *j < *i is false.

The hash_set (and unordered_set) is unordered, so the ordered condition cannot be satisfied.

See tr1::unordered_set union and intersection on how to intersect unordered_sets.