带有提升的不明确选项，因为参数名称以相同的字符串

Question

这是我的问题：

使用lib BOOST（C ++）中的program_options，我有这种奇怪的行为：

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

using namespace boost;
namespace po = boost::program_options;

#include <iostream>

using namespace std;

int main(int ac,char* av[])
{
  int cost_function_param;
  po::options_description desc("Allowed options");
  desc.add_options()
          ("cost-function", po::value<string>()->default_value("WA"), "Cost function (W: wirelength, A: area ratio, C: cut; [WA, WAC, WC, AC]")
          ("cost-function-param", po::value<int>(&cost_function_param)->default_value(0), "Specify the parameter of the cost function. Implemented is \"C\" only for now.")
          ;
  po::variables_map vm;
  try {
    po::store(po::parse_command_line(ac, av, desc), vm);
    po::notify(vm);
  }
  catch(po::error& e)
  {
    std::cerr << "ERROR: " << e.what() << std::endl << std::endl;
    std::cerr << desc << std::endl;
    return -1;
  }
}

案例＃1：

./Debug/partition --cost-function-param 200

没有错误。

案例＃2：

./Debug/partition --cost-function-param 2000 --cost-function WAC

或

./Debug/partition --cost-function WAC

结果：

ERROR: ambiguous option cost-function

Allowed options:
  --cost-function arg (=WA)      Cost function (W: wirelength, A: area ratio,C: cut; [WA, WAC, WC, AC]
  --cost-function-param arg (=0) Specify the parameter of the cost function. Implemented is "C" only for now.

有人有解释吗？谢谢！