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template <class InputIterator1,class InputIterator2,class OutputIterator>  OutputIterator set_difference (InputIterator1 first1, InputIterator1 last1,                                 InputIterator2 first2, InputIterator2 last2,                                 OutputIterator result){while (first1!=last1 && first2!=last2)  {if (*first1<*first2) { *result = *first1; ++result; ++first1; }elseif (*first2<*first1) ++first2;else { ++first1; ++first2; }  }return std::copy(first1,last1,result);}

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// set_difference example#include <iostream>// std::cout#include <algorithm>// std::set_difference, std::sort#include <vector>// std::vectorint main () {int first[] = {5,10,15,20,25};int second[] = {50,40,30,20,10};  std::vector<int> v(10);// 0  0  0  0  0  0  0  0  0  0  std::vector<int>::iterator it;  std::sort (first,first+5);//  5 10 15 20 25  std::sort (second,second+5);// 10 20 30 40 50  it=std::set_difference (first, first+5, second, second+5, v.begin());//  5 15 25  0  0  0  0  0  0  0  v.resize(it-v.begin());//  5 15 25  std::cout <<"The difference has " << (v.size()) <<" elements:\n";for (it=v.begin(); it!=v.end(); ++it)    std::cout <<' ' << *it;  std::cout <<'\n';return 0;}

The difference has 3 elements: 5 15 25