generate filename list with leading zeros

zero_leading_filename_list.cc

#include <iostream>
#include <sstream>
#include <iomanip>

int main() {
  for (int i = 0; i < 10; ++i) {
    std::stringstream ss;
    ss << std::setfill('0') << std::setw(8) << std::fixed << i << ".txt";
    std::cout << ss.str() << std::endl;
  }
}