未存储命令行参数(使用boost)

我想将命令行值存储到变量中。这是我的完整代码:

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

int main(int argc, char *argv[]) {
  int nselect = 100;
  boost::program_options::options_description desc("Allowed options");
  desc.add_options()
        ("help,h", "print usage message")
        ("nselect,N", boost::program_options::value<int>(&nselect), "number to select");
  boost::program_options::variables_map vm;
  boost::program_options::store(boost::program_options::parse_command_line(argc, argv, desc), vm);

  if (vm.count("help")) {
      std::cout << desc << "\n";
      return 0;
  }
  std::cout<<"nselect = "<<nselect<<"\n";
  return(0);
}

我把它编译成 g++ a.cpp -lboost_program_options 然后运行:

$ ./a.out -N 5
nselect = 100

为什么不存储命令行值?

分辨率 :

打电话 notify(vm) 自动将值存储到变量中指定的变量中。或者可以从vm映射它,如下面@matthieu brucher的答案所示。