获得两个集合的并集。两个输入序列须保证已排好序。

数组用的时候

// set_union example

#include <iostream>

#include <algorithm>

#include <vector>

using namespace std;  

int main () {

  int first[] = {5,10,15,20,25};

  int second[] = {50,40,30,20,10};

  vector<int> v(10);                           // 0  0  0  0  0  0  0  0  0  0

  vector<int>::iterator it;  

  sort (first,first+5);     //  5 10 15 20 25

  sort (second,second+5);   // 10 20 30 40 50  

  it=set_union (first, first+5, second, second+5, v.begin());

                                               // 5 10 15 20 25 30 40 50  0  0

  cout << "union has " << int(it - v.begin()) << " elements.\n";

  return 0;

}

set用的时候

// set_union2 example

#include <set>

#include <iterator>

#include <iostream>

#include <algorithm>

using namespace std;  

int main(void)

{

    set<int> a,b,c;

    a.insert(1);

    a.insert(6);

    a.insert(6);

    b.insert(2);

    b.insert(6);

    b.insert(9);  

    //最后一个参数若使用c.begin()会产生编译错误assignment of read-only localtion.  

    set_union(a.begin(), a.end(), b.begin(), b.end(), inserter(c, c.begin()));

    copy(c.begin(), c.end(), ostream_iterator <int> (cout, " "));

    return 0;

}

vector用的时候

// set_union3 example

#include <vector>

#include <iterator>

#include <iostream>

#include <algorithm>

using namespace std;  

int main()

{

    vector<int> a,b,c;

    for(int e=0;e<10;e++)

    {

       a.push_back(e);

       b.push_back(e+5);

    }

    //最后一个参数若使用c.begin(),运行时会出错“Segmentation fault (core dumped)”.

    set_union(a.begin(),a.end(),b.begin(),b.end(),back_inserter(c));

    copy(c.begin(), c.end(), ostream_iterator<int> (cout, " "));

    return 0;

}