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Editorial Team
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Asked: 2026-05-25T06:04:41+00:00

One can use notifier for parsed options only if they have value_semantic. What is

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One can use notifier for parsed options only if they have value_semantic.
What is the best way for no-value options to be automatically handled by the given notifier?

The simple approach is to make a dummy value_semantic with implicit assignment, so a user can pass the option without a value.
This leads to a possibility of explicitly provided values.
One can add a run-time check if the value was provided and throw an error.

Update:
BUT, this doesn’t work in presence of positional options, because a positional option’s value can follow no-value option raising an exception as s given value to it.

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  1. Editorial Team

    One guy OXPEHOMETP on a russian programmers forum gave me a pice of advice to use boost::program_options::bool_switch().

    When defining an option with no value via value-permitted interface, one must pass not boost::program_options::typed_value() as semantics, but bool_switch(). This means that no value can be explicitly taken for this option from the command line.
    One can find info about it at http://www.boost.org/doc/libs/release/doc/html/boost/program_options/bool_switch.html

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