c++ - 使用 Spirit 将 std::vector 解析为结构属性

Question

我有以下文字:

[70000000:45]
4, 5, 6, 7

[60000000:60]
1, 2, 3, 4

[80000:90]
4, 5, 6, 7, 8, 9

带方括号的行包含频率和角度，格式为 [freq:angle]，而后续行是与这些参数相关的数字 vector 。我可以有不同的频率和角度集，并且为每个频率和角度定义了一个 vector 。

我有以下结构:

struct Data {
  std::vector<int> frequencies;
  std::vector<int> elevations;
  std::vector<std::vector<double>> gains;
};

我需要在此结构中存储文件数据:在 frequencies vector 中，我将按顺序从上到下排列所有频率；在 elevations vector 中，除了高程数据之外，我将拥有相同的东西，而在 gains vector 中，我将拥有各自的增益 vector 。

范围是，如果我有一个索引，该索引处的 vector 元素将包含与文件中的频率、海拔和增益相关的数据。

例如，在解析之后，在 index = 1 我将拥有

data.frequencies[1] = 60000000
data.elevations[1] = 60
data.gains[1] = {1, 2, 3, 4}

我需要解析文件以填充结构。我能够解析 frequencies 和 elevations，并将它们存储在 vector 中，但我无法存储增益数据。我需要根据这些数据创建一个 vector vector 。

您可以在下面找到代码；解析后 parsed 填充了频率和高度，我需要增益。我可以做什么来解析它们？

#include <boost/optional/optional_io.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/posix_time/posix_time_io.hpp>
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>

namespace qi = boost::spirit::qi;
namespace px = boost::phoenix;

const std::string file1 = R"xx(
[70000000:45]
4, 5, 6, 7

[60000000:60]
1, 2, 3, 4

[80000:90]
4, 5, 6, 7, 8, 9
)xx";


struct Data {
  std::vector<int> frequencies;
  std::vector<int> elevations;
  std::vector<std::vector<double>> gains;

};

BOOST_FUSION_ADAPT_STRUCT(
  Data,
  (std::vector<int>, frequencies)
  (std::vector<int>, elevations)
  (std::vector<std::vector<double>>, gains)
)

template <typename It, typename Skipper = qi::space_type>
struct grammar : qi::grammar<It, Data(), Skipper> {

  grammar() : grammar::base_type(start) {

    auto frequencyParser = qi::int_[px::push_back(px::at_c<0>(qi::_val), qi::_1)];
    auto elevationParser = qi::int_[px::push_back(px::at_c<1>(qi::_val), qi::_1)];
    auto frequencyElevationParser = qi::lit('[') >> frequencyParser >> qi::lit(':') >> elevationParser >> qi::lit(']');
    auto gainsParser = qi::double_ % qi::lit(','); // Problem here where I want to parse vector rows

    start = *(frequencyElevationParser >> gainsParser);
  }

private:

  qi::rule<It, Data(), Skipper> start;
};

int main() {
  using It = std::string::const_iterator;
  Data parsed;
  bool ok = qi::phrase_parse(file1.begin(), file1.end(), grammar<It>(), qi::space, parsed);
  return 0;
}

Answer 1

本着我经常重复的口头禅的 spirit Boost Spirit: "Semantic actions are evil"?我会使用一个特征，并将每个部分解析为一个 Ast 结构:

qi::rule<It, Data(), Skipper> start;
qi::rule<It, Ast::Data(), Skipper> section;

整个解析器不需要比这更复杂:

section = '[' >> int_ >> ':' >> int_ >> ']' >> double_ % ',';
start = *section;

魔法:

让我们创建一个 Ast 结构，并且只修改它，而不是给定的不切实际的数据类型:

namespace Ast {
    struct Data {
        int frequency;
        int elevation;
        std::vector<double> gains;
    };
}

BOOST_FUSION_ADAPT_STRUCT(Ast::Data, frequency, elevation, gains)

现在，剩下要做的就是告诉 Spirit 如何将 Data 视为 Ast::Data 的容器:

namespace boost { namespace spirit { namespace traits {
    template <> struct container_value<MyLib::Data> { using type = Ast::Data; };

        static bool call(MyLib::Data& c, Ast::Data const& val) {
            c.frequencies.push_back(val.frequency);
            c.elevations.push_back(val.elevation);
            c.gains.push_back(val.gains);
            return true;
        }
    };
} } }

这就简单多了。

演示

Live On Coliru

#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>

namespace qi = boost::spirit::qi;

const std::string file1 = R"xx(
[70000000:45]
4, 5, 6, 7

[60000000:60]
1, 2, 3, 4

[80000:90]
4, 5, 6, 7, 8, 9
)xx";

namespace MyLib {
    struct Data {
        std::vector<int> frequencies;
        std::vector<int> elevations;
        std::vector<std::vector<double> > gains;
    };
}

namespace Ast {
    struct Data {
        int frequency;
        int elevation;
        std::vector<double> gains;
    };
}

namespace boost { namespace spirit { namespace traits {
    template <> struct container_value<MyLib::Data> { using type = Ast::Data; };

    template<> struct push_back_container<MyLib::Data, Ast::Data> {
        static bool call(MyLib::Data& c, Ast::Data const& val) {
            c.frequencies.push_back(val.frequency);
            c.elevations.push_back(val.elevation);
            c.gains.push_back(val.gains);
            return true;
        }
    };
} } }

BOOST_FUSION_ADAPT_STRUCT(Ast::Data, frequency, elevation, gains)

namespace MyLib {
    template <typename It, typename Skipper = qi::space_type>
    struct grammar : qi::grammar<It, Data(), Skipper> {

        grammar() : grammar::base_type(start) {
            using namespace qi;

            section = '[' >> int_ >> ':' >> int_ >> ']' >> double_ % ',';
            start = *section;
        }

      private:
        qi::rule<It, Data(), Skipper> start;
        qi::rule<It, Ast::Data(), Skipper> section;
    };
}

int main() {
    using It = std::string::const_iterator;
    MyLib::Data parsed;
    bool ok = qi::phrase_parse(file1.begin(), file1.end(), MyLib::grammar<It>(), qi::space, parsed);
}