using_getopt.cpp

// adapted from
// https://www.gnu.org/software/libc/manual/html_node/Example-of-Getopt.html
#include <iostream>
#include <unistd.h>

/// main() must be declared with arguments
/// otherwise command line arguments are ignored
int main(int argc, char **argv) {
  bool aflag = 0;
  bool bflag = 0;
  std::string cvalue;
  int cint_value;
  int index;
  int c;

  opterr = 0;

  // expected options are '-a', '-b', and '-c value'
  while ((c = getopt(argc, argv, "abc:")) != -1)
    switch (c) {
    case 'a':
      aflag = true;
      break;
    case 'b':
      bflag = true;
      break;
    case 'c':
      cvalue = optarg;
      cint_value = atoi(cvalue.c_str());
      break;
    case '?':
      if (optopt == 'c')
        std::cerr << "Error: option -" << optopt << " requires an argument."
                  << std::endl;
      else
        std::cerr << "Error: unknown option: " << optopt << std::endl;
      return 1;
    default:
      return 0;
    }

  std::cout << "aflag=" << aflag << " "
            << "bflag=" << bflag << " "
            << "cvalue=" << cvalue << " "
            << "cint_value=" << cint_value << std::endl;

  if (optind < argc) {
    std::cout << "Found positional arguments\n";
    for (index = optind; index < argc; index++)
      std::cout << "Non-option argument: " << argv[index] << "\n";
  }

  return 0;
}