Bryan Green wrote:
> 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)")
>
>
Thanks, that is exactly what I was looking for.
Maybe the documentation should be updated as it says "For the third
option, the user may either provide a single token for the value, or no
token at all", refering to the
("verbose", value<string>()->zero_tokens(), "verbosity level")
Marti
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