Re: [Boost-users] [program_options] Short program options

From: Bryan Green (bgreen_at_[hidden])
Date: 2007-08-15 13:41:02

"Christian Henning" writes:
> Hi there, a while ago I was asking some questions about the short
> option feature. If I'm not mistaken a short option can only be one
> letter long. Is that correct to say?
> 
> In my project I need more than this. So I started to just add the
> short names to the options list like I would do for all options. But
> in this case they would share the same variable. Like this:
> 
>    po::options_description settings( "" );
>    settings.add_options()
>       ( "input_1"
>       , po::value< string >( &_input )
>             ->default_value( "" )
>       , "" )
>       ( "i1"
>       , po::value< string >( &_input )
>             ->default_value( "" )
>       , "" );
> 
> 
> Both options are pointing to the same variable. For some reasons this
> code works only for "input_1" and not for "i1". Why is that? If I use
> --i1="Hallo" the _input is empty.

That makes sense.  The default value for 'input_1' is getting applied *after* the
provided 'i1' value is applied, so it overwrites the 'i1' value.

I'm not %100 sure, but you might get the right effect by initializing '_input' yourself
(or leaving it uninitialized), and remove the 'default_value' settings.
Then you can test the value of '_input' to see if it got set.
The only problem is the usage statement won't print what the default value is, but
is that something you want in this case?

-Bryan