Directly parse and set Gflags from ROS params.

gflags_from_ros_params.cc

// NOTE(mfehr): program_name can be obtained through argv[0].
void parseGflagsFromRosParams(
    const char* program_name, const ros::NodeHandle& nh_private) {
  CHECK_NOTNULL(program_name);
  
  std::vector<google::CommandLineFlagInfo> flags;
  google::GetAllFlags(&flags);
  VLOG(1) << "Parsing gflags from ROS params...";

  std::stringstream ss;

  for (google::CommandLineFlagInfo& flag : flags) {
    if (flag.type == "int32" || flag.type == "uint64" || flag.type == "int64") {
      int32_t ros_param_value;
      if (nh_private.getParam(flag.name, ros_param_value)) {
        ss << "--" << flag.name << "=" << ros_param_value << std::endl;
      }
    } else if (flag.type == "bool") {
      bool ros_param_value;
      if (nh_private.getParam(flag.name, ros_param_value)) {
        ss << "--" << flag.name << "=" << ros_param_value << std::endl;
      }
    } else if (flag.type == "string") {
      std::string ros_param_value;
      if (nh_private.getParam(flag.name, ros_param_value)) {
        ss << "--" << flag.name << "=" << ros_param_value << std::endl;
      }
    } else if (flag.type == "double") {
      double ros_param_value;
      if (nh_private.getParam(flag.name, ros_param_value)) {
        ss << "--" << flag.name << "=" << ros_param_value << std::endl;
      }
    } else {
      LOG(ERROR) << "Cannot parse gflag '" << flag.name
                 << "' from ROS params, type " << flag.type
                 << " is not supported!";
    }
  }
  const std::string ros_param_gflag_file = ss.str();
  CHECK(google::ReadFlagsFromString(
      ros_param_gflag_file, program_name, false /*errors_are_fatal*/));
  VLOG(1) << "\n\nThe following Gflags have been set using ROS params:\n"
            << ros_param_gflag_file << "\n";
}