c++ - 使用 Boost Karma 打印 boost::posix_time::time_duration

Question

我正在尝试为 boost::posix_time::duration 编写一个简单的生成器以在另一个生成器中使用。现在对我来说关键是我想打印的“+”或“-”。到目前为止我所拥有的是:

struct GetSign
{
    template<typename> struct result { typedef char type; };

    template<typename TimeDur>
    const char operator()(const TimeDur& dur) const
    {
        return dur.is_negative() ? '-' : '+';
    }
};

boost::phoenix::function<GetSign>   phx_getsign;

struct TimeDurationGenerator
    : boost::spirit::karma::grammar<boost::spirit::ostream_iterator, boost::posix_time::time_duration()>
{
    TimeDurationGenerator()
        : TimeDurationGenerator::base_type(start_)
    {
        namespace bsk = boost::spirit::karma;
        namespace bpt = boost::posix_time;

        start_
            = sign_[bsk::_1 = phx_getsign(bsk::_val)]
            << bsk::right_align(2,'0')[bsk::int_[bsk::_1 = boost::phoenix::bind(&bpt::time_duration::hours, bsk::_val)]]
            << ':'
            << bsk::right_align(2,'0')[bsk::int_[bsk::_1 = boost::phoenix::bind(&bpt::time_duration::minutes,bsk::_val)]];
    }

    boost::spirit::karma::rule<boost::spirit::ostream_iterator, char()> sign_;
    boost::spirit::karma::rule<boost::spirit::ostream_iterator, boost::posix_time::time_duration()> start_;
};

虽然这确实编译(至少在 clang 上)但它不起作用，因为没有输出。当我将这个生成器包含在另一个生成器中时，输出总是在到达这里时停止。如果我删除规则的 sign_[...] 部分，它就会起作用。

我怎样才能让它工作？

Answer 1

您从未定义过sign_。事实上，你不需要它:

        char_[_1 = phx_getsign(_val)]

但我不会将方钉强行插入圆孔中。如果您需要那种级别的控制，请制作一个原始生成器来执行它。事实上，IO 流操纵器已涵盖:

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#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/spirit/include/karma.hpp>
#include <iomanip>
namespace bsk = boost::spirit::karma;
namespace bpt = boost::posix_time;

template <typename It = boost::spirit::ostream_iterator>
struct TimeDurationGenerator : bsk::grammar<It, bpt::time_duration()>
{
    TimeDurationGenerator() : TimeDurationGenerator::base_type(start_) {
        duration_ = bsk::stream;
        start_    = duration_;
    }
  private:
    struct wrap {
        bpt::time_duration d;
        wrap(bpt::time_duration const& d) : d(d) {}
        friend std::ostream& operator<<(std::ostream& os, wrap const& w) {
            return os << std::setfill('0') << std::internal
                << std::setw(3) << std::showpos   << w.d.hours() << ":"
                << std::setw(2) << std::noshowpos << std::abs(w.d.minutes());
        }
    };
    bsk::rule<It, bpt::time_duration()> start_;
    bsk::rule<It, wrap()> duration_;
};

int main() {
    for (auto str : { "-7:30", "7", "323:87:13" }) {
        std::cout << format(TimeDurationGenerator<>{}, bpt::duration_from_string(str)) << "\n";
    }
}

打印

-07:30
+07:00
+324:27