Simple code to show how to generate permutations in C++

perms.cc

#include <algorithm>
#include <cassert>
#include <iostream>
#include <vector>

using std::copy;
using std::cout;
using std::endl;
using std::vector;

void permutations_recursive(const vector<char> &elems, unsigned long req_len,
			    vector<unsigned long> &pos, vector<bool> &used,
			    unsigned long depth)
{
	// Have we selected the number of required elements?
	if (depth >= req_len) {
		for (unsigned long ii = 0; ii < pos.size(); ++ii)
			cout << elems[pos[ii]];
		cout << endl;
		return;
	}

	// Try to select previously unused elements.
	for (unsigned long ii = 0; ii < elems.size(); ++ii) {
		if (! used[ii]) {
			used[ii] = true;
			pos[depth] = ii;
			permutations_recursive(elems, req_len, pos, used, depth + 1);
			used[ii] = false;
		}
	}
	return;
}

void permutations(const vector<char> &elems, unsigned long req_len)
{
	assert(req_len > 0 && req_len <= elems.size());
	vector<unsigned long> positions(req_len, 0);
	vector<bool> used(elems.size(), false);
	permutations_recursive(elems, req_len, positions, used, 0);
}

const unsigned long num_elements = 5;
const unsigned long perm_len = 3;

int main()
{
	vector<char> elements(num_elements);
	char elements_str[num_elements + 1] = "abcde";
	copy(elements_str, elements_str + num_elements, elements.begin());

	permutations(elements, perm_len);
	return 0;
}