Boost program_options 将多个配置文件解析结果存储到一个 parsed_options

Question

我正在尝试解析命令行提供的任意数量文件中的未注册选项。假设我有文件：

configs0.ini
configs1.ini
configs2.ini

我想支持任意数量的这些。

我的代码（简化）：

namespace po = boost::program_options;
po::options_description cmd_opts{"Options"};
po::options_description config_file_opts;
po::variables_map vm;

cmd_opts.add_options()                                                                                                                                                                                                     
   ("help,h", "Help message")                                       
   ("config_files", po::value<std::vector<std::string>>()->multitoken(), "Configuration files to get settings from")

po::parser.options(reg_config_file_opts).allow_unregistered();

po::store(parse_command_line(argc, argv, cmd_opts), vm);

config_files = vm["config_files"].as<std::vector<std::string>>();
po::parsed_options parsed_opts;

for(auto file : config_files) {
   std::ifstream ifs(file, std::ifstream::in);                                                                                                                                                                             
   if(ifs.fail()) {
      std::cerr << "Error opening config file: " << file << std::endl;
      return false;
   }
   ifs.close();

   <NEED HELP HERE>
   parsed_opt.add(parse_config_file(ifs, reg_config_file_opts));
}

po::store(parsed_opts, vm);

parsed_options 是否有某种 .add 能力？

Answer 1

图书馆distinguishes three layers:

• 描述组件
• 解析器组件
• 存储组件

该设计假设您将使用一组或多组描述与一个或多个解析器，并将结果组合到一个存储中。

实际上，这意味着您将存储到同一个变量映射中，并通知更新任何具有副作用的值语义。

现场演示

• 文件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>());
              }
          }
      }
  }
  

• 文件a.cfg

  foo=foo_val_a
  bar_a=bar_val_a
  

• 文件b.cfg

  foo=foo_val_b
  bar_b=bar_val_b
  

• 文件c.cfg

  foo=foo_val_c
  bar_c=bar_val_c
  

打印：

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"}