Boost program_options store multiple config file parse results into one parsed_options

The library distinguishes three layers:

• the description component
• the parsers component
• the storage component

The design assumes that you will be using one or more sets of descriptions with one or more parsers, and combine the results into one storage.

In practice this means you will store into the same variable map, and notify to update any value-semantics with side-effects.

Live Demo

• File main.cpp

  #include <boost/program_options.hpp> #include <boost/program_options/cmdline.hpp> #include <boost/program_options/config.hpp> #include <fmt/format.h> #include <fmt/ranges.h> #include <fstream> namespace po = boost::program_options; int main() { for (auto args : { std::vector{"test.exe"}, std::vector{"test.exe", "--config_files", "a.cfg", "b.cfg", "c.cfg"}, }) { int const argc = args.size(); char const** argv = args.data(); po::options_description cmd_opts{"Options"}; using values = std::vector<std::string>; cmd_opts.add_options() ("help,h", "Help message") ("config_files", po::value<values>()->multitoken(), "Configuration files to get settings from") ; po::variables_map vm; po::variables_map cfg_vm; // can also reuse vm po::store(parse_command_line(argc, argv, cmd_opts), vm); auto& config_files = vm["config_files"]; if (!config_files.empty()) { po::options_description config_file_opts; config_file_opts.add_options() ("foo", po::value<values>()->composing()) ("bar_a", po::value<values>()->composing()) ("bar_b", po::value<values>()->composing()) ("bar_c", po::value<values>()->composing()) ; for(auto file : config_files.as<values>()) try { std::ifstream ifs(file); po::store(parse_config_file(ifs, config_file_opts), cfg_vm); } catch(std::exception const& e) { fmt::print(stderr, "{}: {}\n", file, e.what()); } fmt::print("Cmdline opts\n"); for (auto& [k, v] : vm) { fmt::print("{}={}\n", k, v.as<values>()); } fmt::print("Combined configs\n"); for (auto& [k, v] : cfg_vm) { fmt::print("{}={}\n", k, v.as<values>()); } } } } 

• File a.cfg

  foo=foo_val_a bar_a=bar_val_a 

• File b.cfg

  foo=foo_val_b bar_b=bar_val_b 

• File c.cfg

  foo=foo_val_c bar_c=bar_val_c 

Prints:

Cmdline opts config_files={"a.cfg", "b.cfg", "c.cfg"} Combined configs bar_a={"bar_val_a"} bar_b={"bar_val_b"} bar_c={"bar_val_c"} foo={"foo_val_a", "foo_val_b", "foo_val_c"}