c++ - boost::program_options 总是用空值解析命令行

Question

在 debian stretch 和 gcc 6.4.0 上，boost 1.66.0

boost::program_options 总是用空值解析命令行。 代码如下:

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <boost/filesystem.hpp>
#include <boost/program_options.hpp>

int main(int argc, char* argv[])
{
    using namespace boost::program_options;
    options_description desc{"Options"};
    desc.add_options()
            ("help,h", "Help screen")
            ("target,t", value<std::string>()->required(), "Set the target.");
    command_line_parser parser{argc, argv};
    parser.options(desc).allow_unregistered().style(command_line_style::default_style | command_line_style::allow_slash_for_short);
    parsed_options parsed_options = parser.run();
    variables_map vm;
    store(parsed_options, vm);
    notify(vm);
    if (vm.count("help"))
    {
        std::cout << desc << std::endl;
        return -1;
    }

    if (vm["target"].empty())
    {
        std::cout << "Error: empty" << std::endl;
        return -1;
    }

    if (vm.count("target"))
    {
        std::string target = vm["target"].as<std::string>();
        std::cout << target << std::endl;
        return -1;
    }
    return 0;
}

然后编译运行

./foo --target start

并且 vm["target"].empty() 总是 TRUE。为什么？？

Answer 1

我只能猜测您运行的二进制文件有误。

Live On Coliru

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <boost/filesystem.hpp>
#include <boost/program_options.hpp>

int main(int argc, char* argv[])
{
    using namespace boost::program_options;
    options_description desc{"Options"};
    desc.add_options()
            ("help,h", "Help screen")
            ("target,t", value<std::string>()->required(), "Set the target.");

    command_line_parser parser{argc, argv};
    parser.options(desc).allow_unregistered().style(command_line_style::default_style | command_line_style::allow_slash_for_short);
    parsed_options parsed_options = parser.run();
    variables_map vm;
    store(parsed_options, vm);
    notify(vm);

    if (vm.count("help"))
    {
        std::cout << desc << std::endl;
        return -1;
    }

    if (vm["target"].empty())
    {
        std::cout << "Error: empty" << std::endl;
        return -1;
    }

    if (vm.count("target"))
    {
        std::string target = vm["target"].as<std::string>();
        std::cout << target << std::endl;
        return -1;
    }
    return 0;
}

./a.out --target HELLOWORLD 的打印:

HELLOWORLD