libconfig++ : adding a setting to the root of the configuration tree

I have a configuration file myCfg.cfg that looks like this :

keyA = 1.0
keyB = 2
keyC = "hello"

Note that all the settings are at the root of the configuration tree.

I want my C++ program to load that file then add a new setting whose key is keyD and assign it integer value 5. Eventually, MyCfg should look like this in memory :

keyA = 1.0
keyB = 2
keyC = "hello"
keyD = 5

First the myCfg.cfg file is loaded to construct MyCfg. Then the setting keyD must be added to the root of MyCfg. The libconfig documentation indicates that the Setting::add() method :

add[s] a new child setting with the given name and type to the setting, which must be a group

However, there isn't any group in MyCfg… So how do I add a setting to the root of a Config object ?

It looks like all what you need is: getRoot ().

Here is example:

#include <iostream>
#include "libconfig.h++"


int main ()
{
    libconfig::Config MyCfg;
    std::string file = "myCfg.cfg";

    try {
        MyCfg.readFile (file.c_str () );

        libconfig::Setting & root = MyCfg.getRoot ();
        // This also works.
        // libconfig::Setting & root = MyCfg.lookup ("");
        libconfig::Setting & keyD = root.add ("KeyD", libconfig::Setting::TypeInt);
        keyD = 5;

        // You dont need it, but it's just for testing.
        MyCfg.writeFile (file.c_str () );
    }
    catch (...) {
        std::cout << "Error caused!" << std::endl;
    }

    return 0;
}