I have an issue with set.union (C++)

Question

I'm trying to union two sets (in a vector).

setA contains a, b. setB contains a, c.

After union, result is supposed to contain a, b, c. However, the program is not working, it is having some kind of debug error.

#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
vector<char> setA;
vector<char> setB;
vector<char> result;
vector<char>::iterator it;

setA.push_back('a');
setA.push_back('b');
setB.push_back('a');
setB.push_back('c');

it = set_union(setA.begin(), setA.end(), setB.begin(), setB.end(), result.begin());

for (int i = 0; i < result.size(); i++)
{
    cout << result[i] << " ";
}

system("PAUSE");
}

Does anyone know what the problem is?

Answer 1

You should either resize the result vector to accommodate the max size of the union, or use std::back_inserter:

it = set_union(setA.begin(), setA.end(),
               setB.begin(), setB.end(),
               back_inserter(result));