c++ boost program options always giving default value

问题

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

回答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.

来源：https://stackoverflow.com/questions/37331901/c-boost-program-options-always-giving-default-value

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