如何比较std :: set的前N个元素？

Question

How can I compare first "n" elements of two sets are equal or not? My following program doesn't work, why?

#include <iostream>
#include <iterator>
#include <set>
#include<algorithm>
using namespace std;

int main ()
{
  int n = 2;
  int myints1[] = {75,23,65,42,13};
  int myints2[] = {70,23,65,42,13};
  set<int> myset1 (myints1,myints1+5);
  set<int> myset2 (myints2,myints2+5);

  if(std::equal(myset1.begin(),myset1.begin() + n ,myset2.begin()))    //error
  std::copy(std::myset1.begin(),myset1.begin() + n,ostream_iterator<int>(cout," ")); //error
  cout << endl;

  return 0;
}

UPDATE:

Is there a way to compare a specific element as well ? Thanks.

Answer 1

std::set iterators are bidirectional, not random-access. You can't say begin() + n with them. Instead you might want to use std::advance .

std::set<int>::iterator it(myset1.begin());
std::advance(it,n);
if(std::equal(myset1.begin(),it,myset2.begin()))
  std::copy(myset1.begin(),it,ostream_iterator<int>(cout," "));