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Stupid question (but I don't find anything on boost.org): how do I catch exceptions from boost::program_options? Invoking

#include <boost/program_options.hpp> #include <iostream> int main(int argc, char** argv){ bool opt; namespace bpo = boost::program_options; bpo::options_description options("Allowed options"); options.add_options() ("opt", bpo::bool_switch(&opt)); bpo::variables_map options_vm; try { bpo::store(bpo::parse_command_line(argc, argv, options), options_vm); bpo::notify(options_vm); } catch(const std::exception &e){ std::cerr << e.what() << std::endl; return 1; } return 0; }

with any option but --opt yields

libc++abi: terminating due to uncaught exception of type boost::wrapexcept<boost::program_options::unknown_option>: unrecognised option '--optnsdf'

Why doesn't catch(const std::exception &e) catch the exception? How do I properly catch catch(const boost::wrapexceptboost::program_options::unknown_option& e)is not intended, also because there can be other program options-related exceptions, such asboost::wrapexceptboost::program_options::invalid_command_line_syntax`, and probably others.

Is there any class hierarchy for boost program options exceptions available online?

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    Boost isn't inheriting std::exception. As for how, the error message tells you exactly what exception gets thrown. Commented Feb 6, 2024 at 16:24
  • If you don't care what you're catching, you can catch(...). Commented Feb 6, 2024 at 16:25
  • The bigger issue appears to be that you are attempting to use an option that you never added. Commented Feb 6, 2024 at 16:32
  • @sweenish What do you mean? It is standard behaviour that programs display a help message if one specifies invalid command line arguments. I want to provide the same behaviour. Commented Feb 6, 2024 at 16:33
  • 1
    Now we're getting close to duplicate territory: stackoverflow.com/questions/8136534/… Commented Feb 6, 2024 at 16:36

1 Answer 1

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You can catch the base exception class program_options::error by reference:

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#include <array> #include <iostream> #include <boost/program_options.hpp> namespace po = boost::program_options; int main() { std::array argv{"demo", "--oops", static_cast<char const*>(nullptr)}; po::options_description options("Allowed options"); bool opt; options.add_options()("opt", po::bool_switch(&opt)); po::variables_map vm; try { store(parse_command_line(argv.size() - 1, argv.data(), options), vm); notify(vm); } catch (po::error const& e) { std::cerr << e.what() << std::endl; options.print(std::cerr); return 1; } }

Printing

unrecognised option '--oops' Allowed options: --opt

Although there's no diagram there is a kind of error reference: https://www.boost.org/doc/libs/1_84_0/doc/html/program_options/reference.html#header.boost.program_options.errors_hpp

The individual types do mention purpose e.g.: "Base class for all errors in the library")

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3 Comments

The fact that this did not work on my machine (Mac with Homebrew llvm) brought me to the real issue: when linking with -L/usr/local/opt/llvm/lib/c++, your code fails. When linking without this (which libc++ am I linking to then?), then your (and my) code runs as expected. Do you know what's going on?
Addendum:" I have little knowledge of how linking works. Is it possible that libboost_program_options.a is built for one libc++, and then linking my program against another libc++ breaks inheritance?
@Bubaya Probably ODR violations (including conflicting RTTI records in different linked objects). There may be more instances of UB as a consequence, so check your build methods closely! Technically it's not "breaking inheritance", just UB

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