set_union

set_intersection

template <class InIter1, class InIter2, class OutIter>    OutIter set_intersection(InIter1 start1, InIter1 end1,                 InIter2 start2, InIter2 end2, OutIter result); template <class InIter1, class InIter2, class OutIter, class Comp>     OutIter set_intersection(InIter1 start1, InIter1 end1,                 InIter2 start2, InIter2 end2,                 OutIter result, Comp cmpfn); 

The set_intersection( ) algorithm produces a sequence that contains the intersection of the two ordered sets defined by start1, end1 and start2, end2. These are the elements found in both the sets. The result is ordered and put into result. It returns an iterator to the end of the result.

The second form allows you to specify a comparison function that determines when one element is less than another.