Question

I have 2 vector of with one has vec1{e1,e2,e3,e4} and the other one with vec2 {e2,e4,e5,e7}

How to effectively get three vector from above vectors such that 1.has elements that is available only in vec1 similarly 2 has only vec2 elements and 3.with common elements

Answer 1

std::set_intersection should do the trick, if both vectors are sorted: http://msdn.microsoft.com/en-us/library/zfd331yx.aspx

std::set_intersection(vec1.begin(), vec1.end(), vec2.begin(), vec2.end(), std::back_inserter(vec3)); 

A custom predicate can be used for the comparison too:

std::set_intersection(vec1.begin(), vec1.end(), vec2.begin(), vec2.end(), std::back_inserter(vec3), my_equal_functor()); 

If they are not sorted, you may of course sort them first, or alternatively, you can iterate through vec1, and for each element, use std::find to see if it exists in vec2.