Re: [Boost-users] program_options: documentation dead end

From: Bryan Green (bgreen_at_[hidden])
Date: 2007-07-19 11:41:44

Steven Mackenzie writes:
> Ian McCulloch wrote:
> > Bryan Green wrote:
> > [snip]
> >> While I'm on the subject, you sometimes see something like the following:
> >>
> >> ./prog -vvv
> >>   or
> >> ./prog -v -v -v
> >>
> >> This would *increment* the verbosity level three times.  I can't see how
> >> to replicate this in program_options.
> > 
> > This is something I have asked about before on this list, but at the time
> > there was no response.  I would be very interested in knowing how to do
> > this using boost::program_options!
> 
> One complete solution has already been posted, but just for diversity, settin
> g a
> notifier function on the variable involves less typing. Something like
> 
> int verbosityLevel;
> ...
> verbosityLevel = 0;
> ...
> void VerbosityWatcher( bool val )
> {
> 	++verbosityLevel;
> }
> ...
> desc.add_options()
>     ("verbose,v",
> 	po::bool_switch()
> 		->notifier( &VerbosityWatcher ),
> 	"print extra information")
>     ;
> 
> Disadvantages are that the value isn't available through vm, the default valu
> e
> isn't set by the usual ->default method or constructor option, ... Probably s
> ome
> some of those could be coded around.
> 
> Personally I think a simple -v 3 is nicer; the -v -v -v style of syntax seems
>  a
> bit verbose to me :-)

Allowing '-v 3' precludes allowing just '-v', which is the common case.

As for notifier, does it really work that way?  I am interested in a way to
track multiple occurrences, but I thought the notifier only got called once
at the end.

-Bryan