Re: [Boost-users] Common parameter on command line and in a config file with sections

Subject: Re: [Boost-users] Common parameter on command line and in a config file with sections
From: Júlio Hoffimann (julio.hoffimann_at_[hidden])
Date: 2011-10-31 16:14:01

Hi Dan,

I've found a long time ago (before know Boost), a header which makes
exactly what you've described:

http://getpot.sourceforge.net/

I'm using it so far, even knowing it's not well designed as Boost
libraries. You can fix some bad habits on it, but all hard work is almost
done.

Regards,
Júlio.

2011/10/31 Gruhn, Dan <dgruhn_at_[hidden]>

>
> Greetings,
>
> I would like to have a parameter "expire-days" that has a default and can
> be set via the command line
>
> --expire-days|-e <days>
>
> and a config file
>
> [foo]
> expire-days = <days>
>
> It would be most elegant to be able to specify things like this (notice
> the automatic storage to the expireDays variable):
>
> namespace bpo = boost::program_options;
> int     expireDays = 30;
>    bpo::options_description desc("Allowed options");
>    desc.add_options()
>        ("expire-days,e",
> bpo::value<int>(&expireDays)->default_value(expireDays), "Number of days
> before files expire")
>        ;
>
>    bpo::options_description configFileDesc;
>    configFileDesc.add_options()
>        ("foo.expire-days", bpo::value<int>(&expireDays), "")
>        ;
>
>    bpo::variables_map varMap;
>
>    try
>    {
>        // Attempt to parse the configuration file.
>        std::ifstream cfg("/tmp/all.cfg");
>        if (cfg.is_open())
>        {
>            std::cout << "Opened /tmp/all.cfg" << std::endl;
>            static const bool   allowUnregistered = true;
>            bpo::store(bpo::parse_config_file(cfg , configFileDesc,
> allowUnregistered), varMap);
>        }
>        // Parse the command line
>        bpo::store(bpo::parse_command_line(argc, argv, desc), varMap);
>
>        bpo::notify(varMap);
>    }
>    std::cout << "Expire days: " << expireDays << std::endl;
>
>
> My code may be strange but I am trying to find the right order and
> combination of adding options, parsing, storing, and notifying that gives
> the command line priority over the config file which in turn has priority
> over the 30 day default. Oddly enough, it doesn't seem to make much
> difference which order I use, the config file seems to have precedence This
> is not what I expected so perhaps I'm doing something wrong but I can't
> find it.
>
> I know that I can accomplish this via extra code on my part, but I'm
> trying to come up with a general scheme that would work for multiple
> programs with multiple variables using a common config file and the simpler
> the better. The documentation mentions using sections in config files but
> doesn't give much detail. Can anyone help me here or at least describe for
> me which of add_options, parse_*, store, and notify does the following:
>
> 1) Sets the default value
> 2) Marks that a value has been set from the command line/config file.
> 3) Actually does the store to the given variable.
> 4) What does notify do?
>
> I've tried (and continue to try) looking through the code but am having
> problems find the right place examine. I'll take pointers in that area as
> well.
>
> This does not seem like an exotic use case. Has anyone else accomplished
> this or something like it?
>
> As always, any help of any kind will be greatly appreciated.
>
> Dan
>
>
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