c++ boost program options always giving default value

Question

I'm struggling to get boost program options to work properly. I need to be able to start my program from the terminal window (Linux) with an optional argument that takes a value. No matter what I did, this would not work; no matter what value I typed from the terminal, it just returned the default value. Furthermore, if I did not include the option in my termina command, it returned with

terminate called after throwing an instance of      'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injec    tor<std::logic_error> >'                                                                                                                                                   
 what():  character conversion   failed                                                                                                              
Aborted (core dumped)

So I found a minimal example on the internet to see if it was something I had done wrong. Here is the example I found that does a similar thing that I need:

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

namespace po = boost::program_options;

int main  (int argc, char* argv[]) {

po::options_description desc("Usage");
desc.add_options()
  ("robots", po::value<int>()->default_value(3), 
 "How many robots do you want to send on a murderous rampage?");

po::variables_map opts;
po::store(po::parse_command_line(argc, argv, desc), opts);

try {
   po::notify(opts);
} 
catch (std::exception& e) {
   std::cerr << "Error: " << e.what() << "\n";
   return 1;
}

int nRobots = opts["robots"].as<int>(); 
// automatically assigns default when option not supplied by user!!

std::cout << nRobots << " robots have begun the silicon revolution" 
    << std::endl;
 return 0;
} 

This does exactly the same thing however, and I am starting to think this is either a bug in Boost (unlikely I guess) or something about my system that it doesn't like?

Could anybody hint at what might be wrong please? Thanks

Mello

This works correctly for me. Please make sure that your reproducible examples actually reproduce the error in question. – Hemmer

Your code works here. – Celka

@Hemmer As I said in my post, that code does reproduce the error on my machine, and suspected it was a bug either with my version of Boost (v1.60) or something on my system. At least now I know the code does work, thank you. – Mello

Which version of Boost are you using, and what command are you compiling your program with? – Hemmer

@Hemmer Using v1.60. It compiles fine, but the command I'm compiling with is: g++ popt_test.cpp -lboost_program_options – Mello

@Hemmer I have just removed and reinstalled boost and it seems to now be working fine: both my test example and my own program. Thanks for the help – Mello

Answer 1

I ran into the exact same problem transitioning from 1.58 to 1.61.
My problem was that I was linking 1.61 boost header code with old 1.58 shared libraries.

You may have installed a newer version of boost, but that doesn't mean you still aren't linking with old boost libraries. Check your linker. Check your system files.
A good check you can do on your program, is to run it through gdb, have it crash, and look at the backtrace (bt). It will show the boost version numbers in the backtrace. See if it matches what you expected.

If relevant, I was on Ubuntu and built from source:

sudo ./bootstrap.sh --prefix=/usr
sudo ./b2 install threading=multi link=shared

This resulted in my library files being located at /usr/lib/libboost*.
However, my linker was looking in /usr/lib/x86_64-linux-gnu/libboost*.

A simple cp -Pf over the old files solved my problem.

Endive