importing an array or list setting using libconfig

Question

I've never really worked with configuration files before, but I'm interested in using one as a parameter file for an engineering code I'm writing.

Not being a professional programmer, I've spent two days trying to figure out how to import a simple list or array setting using libconfig and I can't seem to get anywhere. Roughly working from the example here, I'm able to successfully import scalar settings, like

(importtest.cfg)

mynumber = 1;

using a main function like

  Config cfg;

  // check for I/O and parse errors
  try
    {
      cfg.readFile("importtest.cfg");
    }
  catch(const FileIOException &fioex)
    {
      std::cerr << "I/O error while reading config file." << std::endl;
      return(EXIT_FAILURE);
    }
  catch(const ParseException &pex)
    {
      std::cerr << "Parse error at " << pex.getFile() << " : line " << pex.getLine() << " - " << pex.getError() << std::endl;
      return(EXIT_FAILURE);
    }

  // look for 'mynumber'
  try
    {
      int number = cfg.lookup("mynumber");
      std::cout << "your number is " << number << std::endl;
    }
  catch(const SettingNotFoundException &nfex)
    {
      std::cerr << "No 'mynumber' setting in configuration file." << std::endl;
    }

I get the expected output

your number is 1

But I am unable to import a simple list setting, such as

mylist = (1,2,3,4);

In a similar way. I've tried a number of solutions (like creating a root setting), but don't really understand any of them.

Any help is much appreciated.

Answer 1

It also took me a while to figure this out. This is how I finally did it, based on https://github.com/hyperrealm/libconfig/blob/master/examples/c%2B%2B/example1.cpp:

example_simple.cfg file:

albums  =
  (
    { 
      title      = "one title";
      year       = 2017;
      songs      = ["first song", "second song"];
    },
    { 
      title      = "another title";
      year       = 2015;
      songs      = ["first song", "second song", "third song"];
    }
  );

Read it with libconfig C++ API:

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <vector>
#include <libconfig.h++>

using namespace std;
using namespace libconfig;

int main(int argc, char **argv)
{
  Config cfg;

  // Read the file. If there is an error, report it and exit.
  try
  {
    cfg.readFile("../example_simple.cfg");
  }
  catch(const FileIOException &fioex)
  {
    std::cerr << "I/O error while reading file." << std::endl;
    return(EXIT_FAILURE);
  }
  catch(const ParseException &pex)
  {
    std::cerr << "Parse error at " << pex.getFile() << ":" << pex.getLine()
              << " - " << pex.getError() << std::endl;
    return(EXIT_FAILURE);
  }

  const Setting& root = cfg.getRoot();
  try
  {
    const Setting &albums = root["albums"];
    for(int i = 0; i < albums.getLength(); ++i)
    {
      const Setting &album = albums[i];
      string my_title;
      int my_year;
      vector<string> my_songs;

      album.lookupValue("title", my_title);
      cout << "title: " << my_title << endl;
      album.lookupValue("year", my_year);
      cout << "year: " << my_year << endl;

      const Setting &songs_settings = album.lookup("songs");
      vector<string> songs;
      for (int n = 0; n < songs_settings.getLength(); ++n)
      {
          my_songs.push_back(songs_settings[i]);
          cout << "song number " << n << ": " << my_songs[n] << endl;
      }
    }
  }
  catch(const SettingNotFoundException &nfex)
  {
    // Ignore.
  }

  return(EXIT_SUCCESS);
}