gistfile1.c

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

void pick(const std::vector<int>& v)
{
  size_t sz = v.size();
  for (size_t n = 1; n <= sz; ++n) {
    std::vector<bool> sel(sz);
    std::fill_n(sel.begin(), n, true);
    do {
      int r = 0;
      for (size_t i = 0; i < sz; ++i) {
        if (sel[i])
          r = (r * 10) + v[i];
      }
      std::cout << r << std::endl;
    } while (std::prev_permutation(sel.begin(), sel.end()));
  }
}

int main()
{
  pick({1,2,3});
  // OUTPUT: 1 2 3 12 13 23 123
}