Actually one shouldn't even try to write a parser on Windows, the API functions Get/SetPrivateProfileString are the preferred way of interacting with INI files. (And the Registry is of course preferred over ini files since win 95.)
I think that they officially deprecate the registry now. I believe that .Net pushes people toward config files in the APPDATA or the COMMON_APPDATA location as returned by SHGetFolderPath. These usually resolve to "c:/Documents and Settings/username/Application Data" and "c:/Documents and Settings/All Users/Application Data" directories respectively. I don't know if there is any way to abstract these locations in the program_options library. It would be kind of a nice insulation layer. Something like: boost::filesystem::path get_user_config_path(); boost::filesystem::path get_system_config_path(); And make them call SHGetFolderPath on Windows or return "~/" or "/etc/" on posix systems. I can't speak for other kinds of systems though. Anyway, just a thought. Jason