How to properly use boost::program_options::implicit_value for vector of string?

Question

Proof of code:

boost::program_options::options_description options;

Parser::Parser(): options("Allowed options")
{
  options.add_options()
  ("help,h", "produce help message")
  ("type,t", po::value<std::string>()->required()->implicit_value(""), "Type")
}

This line is ok:

("type,t", po::value<std::string>()->required()->implicit_value(""), "Type")

How can I add this line to work correctly?:

("file,f", po::value< std::vector<std::string> >()->required()->multitoken()->implicit_value(std::vector<std::string>(0,"")), "File(s)")

Here is vector of string-s.

score 2 · Answer 1 · answered Oct 31 '15 at 19:35

You just need to help the options-description to know how to present the default value to the end user.

That is, usually implicit_value would use lexical_cast<> to get the textual representation, but that (obviously) doesn't work for vector<string>. So, supply your own textual representation:

("file,f", po::value<strings>()->required()
    ->implicit_value(strings { "santa", "claus" }, "santa,claus"), "File(s)");

Full Demo

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

namespace po = boost::program_options;

int main(int argc, char** argv) {
    po::options_description options/*("Allowed options")*/;

    using strings = std::vector<std::string>;

    options.add_options()
        ("help,h", "produce help message")
        ("file,f", po::value<strings>()->required()->implicit_value(strings { "santa", "claus" }, "santa,claus"), "File(s)");

    std::cout << options << "\n";

    po::variables_map vm;
    po::store(po::parse_command_line(argc, argv, options, po::command_line_style::default_style), vm);
    po::notify(vm);

    auto types = vm["file"].as<strings>(); 
    for (auto t : types)
        std::cout << "Got: " << t << "\n";
}

Prints:

  -h [ --help ]                      produce help message
  -f [ --file ] [=arg(=santa,claus)] File(s)

Got: santa
Got: claus

How to properly use boost::program_options::implicit_value for vector of string?

1 Answers1