[Boost-users] Re: dynamically created program options

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-09-08 02:19:00

Hi Rodolfo,

> Hi, I wonder if it's possible to handle dynamically created program
> options with boost::program_options. For instance: I have a config file
> that specifies configure options for dynamic loaded modules in my
> project. So the cfg file would be:
> 
> [module.foo1]
> module_file = foo.so
> listen_port = 564
> enabled = true
 
> As can be seen, foo1, foo2 and bar1 names are defined by the user in the
> configure file, and the program doesn't know about them before parsing
> the configuration. But if we parse that (somehow), an exception saying
> that the option "module.foo1.module_file" is invalid will be thrown. Can I
> manage the options_description "on the fly"?

Not exactly "on the fly". In program_options, parsing is separated from any
semantic work, so it's not possible to add new items to options_description
while the file is being parsed.

You'd need to "prescan" the config file and then declare the necessary
options. Luckily, to "prescan" the config file you can use "*" in option
names. If you declare "module.*" option, which will catch everything. The
problem is that all options will have the same time.

So, after this "prescan" parsing you can collect the list of modules, and
declare "real" options: "module_file", "listen_port" and so on.

I attach the example and a config file which produce this:

  bar : bar.so : 500
  foo : foo.so : 400

HTH,
Volodya