question abt STL algorithim 'difference'

irfanhab · 07-30-2005, 12:39 PM

Consider this piece of C++ code:

Code:

{

  int A1[] = {1, 3, 5, 7, 9, 11};
  int A2[] = {1, 1, 2, 3, 5, 8, 13};
int N1=5;
int N2=6;
  cout << "Difference of A1 and A2: ";
  set_difference(A1, A1 + N1, A2, A2 + N2,
                 ostream_iterator<int>(cout, " "));
}

The the difference is outputted to STDout, I want to difference to be outputted into another set, certainly the ostream_iterator<int> has to redirected to seomthing else, which would assign all the values to a new set, how do I do it?

carl.waldbieser · 07-30-2005, 04:38 PM

Code:

#include <iostream>
#include <algorithm>
#include <iterator>
#include <vector>

int main() 
{
	int A1[] = {1, 3, 5, 7, 9, 11};
	int A2[] = {1, 1, 2, 3, 5, 8, 13};
	std::vector<int> Vout;
	int Aout[] = {0,0,0,0,0,0,0};
	int N1=5;
	int N2=6;
	std::cout << "Difference of A1 and A2: ";
	std::set_difference(A1, A1 + N1, A2, A2 + N2,
						std::ostream_iterator<int>(std::cout, " "));
	std::cout << "\n";

	//Insert results into a vector.
	std::set_difference(A1, A1 + N1, A2, A2 + N2, std::back_inserter(Vout));
	
	//Copy vector elements into an array.
	for(int i=0; i< Vout.size(); ++i)
	{
		Aout[i] = Vout[i];
	}
	//Copy array to standard output.
	std::copy(Aout, Aout + 7, std::ostream_iterator<int>(std::cout, " "));
	std::cout << "\n";
	return 0;
}

The "inserter" iterator adapters are pretty useful in this regard, but they only work with data elements that provide the required methods (e.g. "push_back()" or "push_front()). So I insert into another STL container and copy it to an array (which is presumably what you want. I made the output array as large as the largest input array so I wouldn't overwrite the end.

irfanhab · 07-30-2005, 09:38 PM

Thanks, for ur prompt reply