自定义验证器不允许 default_value

Question

我正在尝试使用自定义验证器而不是重载 operator>> 来支持我的选项解析中的枚举类型。我做了以下事情：

#include <iostream>

#include <boost/program_options.hpp>

enum class MyEnum
{
    OneThing,
    AnotherThing
};

void validate(boost::any& v, const std::vector<std::string>& values,
              MyEnum*, int)
{
    // parse the enum from values[0]
    std::cout << "Test" << std::endl;
    MyEnum enumValue = MyEnum::OneThing;
    v = enumValue;
}

int main(int argc, char*argv[])
{
    namespace po = boost::program_options;

    po::options_description desc("Options");

    //desc.add_options()("myEnum", po::value<MyEnum>(), "MyEnum value"); // works fine
    desc.add_options()("myEnum", po::value<MyEnum>()->default_value(MyEnum::OneThing), "MyEnum value"); // compiler error: Source type is not streamable

    po::variables_map vm;
    po::store(po::parse_command_line(argc, argv, desc), vm);
    po::notify(vm);

    MyEnum myEnum = vm["myEnum"].as<MyEnum>();

    return 0;
}

只要我不尝试设置default_value，它就可以正常工作，但是当我指定默认值时，我会得到error: static assertion failed: Source type is neither std::ostream able nor std::wostream able。我还需要做什么（不重载流运算符，据我所知，这是使用验证器的全部意义）来允许自定义类型获取 default_value？

Answer 1

你可以设置一个默认值，但是，它需要知道如何在描述中表示默认值。

由于枚举不是流式的，自动方式不起作用，所以你必须指定它，例如：

default_value(MyEnum::OneThing, "OneThing")

Live On Coliru

#include <iostream>

#include <boost/program_options.hpp>

enum class MyEnum
{
    OneThing,
    AnotherThing
};

void validate(boost::any& v, const std::vector<std::string>& values,
              MyEnum*, int)
{
    // parse the enum from values[0]
    std::cout << "Test" << std::endl;
    MyEnum enumValue = MyEnum::OneThing;
    v = enumValue;
}

int main(int argc, char*argv[])
{
    namespace po = boost::program_options;

    po::options_description desc("Options");

    //desc.add_options()("myEnum", po::value<MyEnum>(), "MyEnum value"); // works fine
    desc.add_options()("myEnum", po::value<MyEnum>()->default_value(MyEnum::OneThing, "OneThing"), "MyEnum value");

    po::variables_map vm;
    po::store(po::parse_command_line(argc, argv, desc), vm);
    po::notify(vm);

    MyEnum myEnum = vm["myEnum"].as<MyEnum>();
    std::cout << std::boolalpha << (myEnum == MyEnum::OneThing) << "\n";
}

打印

true