Re: [Boost-users] Questions about using program_options

From: Rupert Bruce (rupert_at_[hidden])
Date: 2008-05-24 11:03:31

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Frank Birbacher wrote:
> Hi!
> 
> Rupert Bruce schrieb:
>> So anywhere in my code I can do, for example:
>>     if (PropertyCatalog::getBooleanProperty("testapp.profile",false))
>>         {
>>         profile.append(currentStatus);
>>         }
> 
> Which has a design flaw, I think. I just got rid of a lot of such 
> function calls in a project I'm working at. The flaw: do not keep 
> configuration default values distributed in the code. What if the 
> default value needs to change? It does commonly change for directory 
> paths. If you now tell me to always write the correct value into the 
> config file, then I wouldn't need any default value at all and I could 
> just remove them. And if you need different default values for the same 
> key in different places, then you simply need also different keys.
> 
> I now have "getConfig" calls without defaults in the call.
> 
> Frank
> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
> 
> 
Personally, I like the defaults (I typically replace a hard-coded value
in the code with a call to PropertyCatalog so the default is obvious).
One advantage of Polymorphism is that I don't need to specify a default:
   PropertyCatalog::getBooleanProperty("testapp.profile")

As you mention, file paths are a common default that changes - one that
I frequently have to override on the command line is the path to the
config file itself. One benefit of boost::program_options is that I have
that flexibility. This is from a test case with no properties:

int main(int argc, char *argv[])
    {
    PropertyCatalog::populate(argc, argv);
    string
log_config_file=PropertyCatalog::getStringProperty("config.logging",
"../config/log4cxx.properties");
    log4cxx::PropertyConfigurator::configure(LOG4CXX_FILE(log_config_file));

    if (PropertyCatalog::isDefined("help"))
        {
        PropertyCatalog::logPropertyCatalog();
        }
    return UnitTest::RunAllTests();
    }

void PropertyCatalog::populate(int argc, char **argv)
    {
    options_description general("General options");
    general.add_options()
    ("help", "produce a help message")
    ("config", value<string>(),"override the default config file name")
    ("version", "output the version number");

    string defaultConfigFileName =
static_cast<string>(argv[0])+".properties";
    string config_file=PropertyCatalog::getStringProperty("config",
defaultConfigFileName);

    options_description cmdline_options;
    cmdline_options.add(general);

    options_description config_file_options;
    config_file_options.add(general);

    //class variable 'visible' holds the set of option_descriptions that
the user
    //may want to have listed via logPropertyCatalog()
    visible.add(general);

    store(parse_command_line(argc, argv, cmdline_options), vm);

    //load the config file
    ifstream ifs(config_file.c_str());
    store(parse_config_file(ifs, config_file_options), vm);

    notify(vm);
    }

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