boost program_options custom parsing

Question

Is there a way to have something like

myapp hostname:port

parsed by boost program_options? I'm also using other options and I would love to use boost program_options without having to roll my own parser for argc/argv.

I tried with some combinations of

desc.add_options()
    ("help", "list all available options")
    (new MyCustomValue(&store_var), "")

but it didn't work

Answer 1

As Dan Mašek writes, this looks more fitting for a positional argument. Since you specify a specific structure for the option, though, you might want to add std::regex_match.

Say you start with

#include <string>
#include <iostream>
#include <regex>
#include <boost/program_options.hpp>

using namespace std;
using namespace boost::program_options;

int main(int argc, const char *argv[]) {
    try {
        options_description desc{"Options"};
        desc.add_options()
            ("help,h", "Help screen")
            ("ip_port", value<std::string>()->required(), "ip:port");

        positional_options_description pos_desc;
        pos_desc.add("ip_port", -1);

        command_line_parser parser{argc, argv};
        parser.options(desc).positional(pos_desc).allow_unregistered();
        parsed_options parsed_options = parser.run();

        variables_map vm;
        store(parsed_options, vm);
        notify(vm);

        const auto ip_port = vm["ip_port"].as<string>();

At this point, we have the user's input for ip_port. We can define a regex to match it. Note that first part can be a string (e.g., localhost), but the second part must be an integer:

        const regex ip_port_re("([^:]+):([[:digit:]]+)");
        smatch ip_port_match;
        if(!regex_match(ip_port, ip_port_match, ip_port_re)) 
             throw validation_error{validation_error::invalid_option_value, ip_port, "ip_port"};
        cout << "ip: " << ip_port_match[1] << " port: " << ip_port_match[2] << endl;
    }
    catch (const error &ex) {
        cerr << ex.what() << '\n';
    }
}

When running it, it looks like this:

$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out 127.0.0.1:30
ip: 127.0.0.1 port: 30
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out localhost:30
ip: localhost port: 30
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out localhost:30d
the argument for option 'localhost:30d' is invalid
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out 
the option '--ip_port' is required but missing
$ g++ --std=c++11 po.cpp -lboost_program_options && ./a.out localhost:30 foo
option '--ip_port' cannot be specified more than once