argoneus argoneus - 3 months ago 6
C++ Question

Boost program options with default values always present when using vm.count()

I've been trying to validate my passed options with boost::program_options. My command has several modes, each of which have associated params that can be specified. What I'm trying to do is ensure these associated params are passed with the mode, i.e.

unicorn --fly --magic-wings-threshold


Where
--fly
is the mode and
--magic-wings-threshold
is an associated param. What I've noticed is if
--magic-wings-threshold
has a default value, e.g.

("magic-wings-threshold,w", po::value<double>(&wings_thresh)->default_value(0.8, "0.8"),
"Magic wings maximum power"
)


then I can't use

if (vm.count("magic-wings-threshold")( {
// do stuff
}


to detect if the user passed that param.

It appears that default value params are always passed and detected in
vm.count()
. Does anyone know a workaround or alternative?

Answer

use boost::program_options::variable_value::defaulted()

if (vm["magic-wings-threshold"].defaulted())  {
    // assume defaulted value
} else {
    // one was provided
}