boost-program-options: notifier for options with no value

Question

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?

Answer 1

This is full example on providing a flag as an option to complement current answers:

#include 

#include 

using namespace std;

namespace po = boost::program_options;


int main(int ac, char* av[])
{
    po::options_description desc("Allowed options");

    desc.add_options()
        ("help", "produce help message")
        ("overwrite,o", po::bool_switch()->default_value(false),
                        "enable file overwrite");

    po::variables_map vm;
    po::store(po::parse_command_line(ac, av, desc), vm);

    boolalpha(cout);  // display true and false for bool
    cout << "overwrite is: " << vm["overwrite"].as() << endl;

    return 0;
}

Mine qmake pro file (I use Qt 5.4):

TEMPLATE = app
CONFIG += console
CONFIG += c++14
CONFIG -= app_bundle
CONFIG -= qt

SOURCES += main.cpp


include(deployment.pri)
qtcAddDeployment()

INCLUDEPATH += /opt/boost_1_57_0

unix:!macx: LIBS += -L/opt/boost_1_57_0/stage/lib -lboost_program_options

Running the program without any options results in:

./untitled4
overwrite is: false

However running with '-o' option/flag gives:

./untitled4 -o
overwrite is: true