Question

I am writing the following code on boost’s program_options (version 1.42). This seems straight-forward and taken pretty much as is from the tutorial. However, I get a “multiple_occurrences” error. Further investigation discovers that it’s (probably) the “filename” parameter that raises it.

The parameters I am giving are:

3 1 test.txt 100

I have no insight to it whatsoever.. any help will be appreciated.

po::options_description common("Common options");

common.add_options()
    ("help", "produce help message")
    ("motif_size", po::value<int>(&motif_size), "Size of motif (subgraph)")
    ("prob", po::value<double>(&prob), "Probably to continue examining an edge")
    ("filename", po::value<string>(&input_filename), "Filename of the input graph")
    ("repeats", po::value<int>(&n_estimates), "Number of estimates")
    ;

po::options_description all;
all.add(common);

po::positional_options_description p;
p.add("motif_size", 0).add("prob", 1).add("filename", 2).add("repeats", 3);

po::variables_map vm;   
po::store(po::command_line_parser(argc, argv).
      options(all).positional(p).run(), vm);
po::notify(vm); 

Answer 1

EDIT:

the second parameter to po::positional_options_description::add is the max count, not the position. The position is implied in the order you specify the positional options. So

p.add("motif_size", 0).add("prob", 1).add("filename", 2).add("repeats", 3);

should be

p.add("motif_size", 1).add("prob", 1).add("filename", 1).add("repeats", 1);

Here’s a compilable snippet

include <boost/program_options.hpp>

#include <iostream>
#include <string>

int
main(unsigned argc, char** argv)
{
    namespace po = boost::program_options;
    po::options_description common("Common options");

    common.add_options()
        ("help", "produce help message")
        ("motif_size", po::value<int>(), "Size of motif (subgraph)")
        ("prob", po::value<double>(), "Probably to continue examining an edge")
        ("filename", po::value<std::string>(), "Filename of the input graph")
        ("repeats", po::value<int>(), "Number of estimates")
        ;

    po::options_description all;
    all.add(common);

    po::positional_options_description p;
    p.add("motif_size", 1).add("prob", 1).add("filename", 1).add("repeats", 1);

    po::variables_map vm;
    try {
        po::store(po::command_line_parser(argc, argv).
                options(all).positional(p).run(), vm);
        po::notify(vm); 
    } catch ( const boost::program_options::error& e ) {
        std::cerr << e.what() << std::endl;
    }

    return 0;
}

and sample invocation.

macmini:~ samm$ g++ parse.cc -lboost_program_options
macmini:~ samm$ ./a.out 3 1 test.txt 100
macmini:~ samm$ 

My original answer is below.

---

What version of program_options? I had the same problem using boost 1.39, to solve it I ended up using boost 1.42.

Here’s a link to the ticket describing the problem, and a patch to apply if you don’t want to or can’t upgrade your copy of boost. To use the new functionality, do something like this

try {
    // argument parsing goes here
} catch ( const boost::program_options::multiple_occurrences& e ) {
    std::cerr << e.what() << " from option: " << e.get_option_name() << std::endl;
}