Good, simple configuration library for large c++ project?

We are developing a rather large project in C++, where many components require configuration parameters. We would like to use a central place to configure everything (like a registry), preferably with a nice and simple GUI (e.g. like Firefox's about:config) and a simple API.

I am pretty sure this that many applications have this kind of problem, but could not find any libraries available that can be readily used for this. Does anyone know of a good (preferably free) library to use for this?

This should work cross platform in Windows and Linux.

From stackoverflow

• I've used a modified version of John Torjo code from TechRepublic/DDJ (source)

• The multi platform ACE library has a configuration class that uses config files that have the Windows .ini format.

• I've often used a simple wrapper around pugxml. I find that creating a configuration class with parameter validation for enumerated types and so on makes the rest of the code much cleaner. If you are just dealing with key/value pairs you will have to validate the data all throughout your code. By writing a custom class for each application you can put all that in one place.

• boost::program_options provides unified (and cross platform) support for configuration from command line, environment variables and configuration files. It seems like it ought to scale to multiple bits of a large software system registering an interest in various parameters (e.g option groups). Not much help with the GUI or persistence side of things though (but then what's wrong with editing a config file with a text editor ?).