Marti Cuquet writes:
> Hello,
>
> I am trying to use an option that can have either zero or one arguments.
>
> I have seen an example in the documentation claiming that the following
> code would allow the user to provide either zero or one tokens to option
> 'verbose', but instead it throws an exception "extra parameter" when one
> token is given.
>
> So the question is, does zero_tokens() allow the user to specify a value?
>
> options_description desc;
> desc.add_options()
> ("help", "produce help message")
> ("compression", value<string>(), "compression level")
> ("verbose", value<string>()->zero_tokens(), "verbosity level")
> ("email", value<string>()->multitoken(), "email to send to")
> ;
There is an undocumented "implicit_value" feature that may be what you are
looking for. It allows zero or one token in the style of
getopt/getopt_long:
options_description desc;
desc.add_options()
("help", "produce help message")
("verbose,v", po::value<int>()->implicit_value(1),
"enable verbosity (optionally specify level)")
-bryan
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