c++ - Boost.Spirit语法问题

Question

我正在尝试解析术语信息定义文本文件。我是 Boost.Spirit 的新手。我从只解析注释行、空行和终端定义的简单语法开始。正如语法中的代码注释所示，取消对 definition 的 [_val = _1] 的注释会中断编译。为什么？我可以修复它吗？

如果我忽略实际的 terminfo 文件，我希望下面的代码能够解析这种文本:

# comment line

first definition line
  second 
  third line

# another comment line

代码:

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/qi_eol.hpp>
#include <boost/spirit/include/qi_eoi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/spirit/include/phoenix_object.hpp>
#include <vector>
#include <iostream>
#include <string>

namespace termcxx
{

namespace parser
{

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

//using qi::double_;
using ascii::space;
//using px::ref;
using px::construct;

//using qi::eps;
//using qi::lit;
using qi::_val;
using qi::_1;
using ascii::char_;
using qi::eol;
using qi::eoi;


struct context
{
    int dummy;

    context () = default;
    context (context const &) = default;
    context (std::vector<char> a)
    { }
    context (std::vector<char> a, std::vector<char> b)
    { }
};

} }


BOOST_FUSION_ADAPT_STRUCT(
    termcxx::parser::context,
    (int, dummy))


namespace termcxx
{

namespace parser
{

template <typename Iterator>
struct parser
    : qi::grammar<Iterator, context()>
{
    qi::rule<Iterator, std::vector<char> > comment_line
    = (*space >> '#' >> *(char_ - eol) >> (eol | eoi))[_val = _1]
        ;

    qi::rule<Iterator, std::vector<char> > empty_line
    = (*space >> (eol | eoi))[_val = _1]
        ;

    qi::rule<Iterator, std::vector<char> > def_first_line
    = (+(char_ - eol) >> (eol | eoi))[_val = _1]
        ;

    qi::rule<Iterator, std::vector<char> > def_subsequent_line
    = (+space >> +(char_ - eol) >> (eol | eoi))[_val = _1]
        ;

    qi::rule<Iterator, std::vector<char> > definition
    = (def_first_line >> *def_subsequent_line)//[_val = _1] // Uncommenting the [_val = _1] breaks compilation. Why?
        ;

    qi::rule<Iterator, context()> start
    = (*(comment_line
            | empty_line
            | definition))[_val = construct<context> ()]
        ;

    parser()
        : parser::base_type(start)
    { }
};

template struct parser<std::string::iterator>;

} // namespace parser

} // namespace termcxx

Answer 1

你为什么坚持指定[_val=_1] ？这是多余的，因为默认属性传播会执行此操作。其实很痛，见下文

接下来是(def_first_line >> *def_subsequent_line)的属性类型(显然)与 std::vector<char> 不兼容.也许你可以

• 只使用默认的属性传播(它有足够的智慧继续追加)
• 使用raw[]得到完整匹配的输入
• 定义BOOST_SPIRIT_ACTIONS_ALLOW_ATTR_COMPAT (我不确定这是否得到很好的支持)

此外，

• 你可以替换std::vector<char>与 std::string当依赖自动属性传播时
• 您可以检测解析器表达式的实际公开类型:Detecting the parameter types in a Spirit semantic action

更新

还有几个问题:

• 您拼错了大多数规则的属性类型(缺少 () ):

  qi::rule<Iterator, std::string()> comment_line;
  qi::rule<Iterator, std::string()> empty_line;
  qi::rule<Iterator, std::string()> def_first_line;
  qi::rule<Iterator, std::string()> def_subsequent_line;
  qi::rule<Iterator, std::string()> definition;
  

• empty_line匹配于 eoi在输入结束时导致无限循环

• 使用char_也接受空格(改用 graph:)

      def_first_line      = graph >> +(char_ - eol)         >> (eol|eoi);
  

• 使用qi::space也吃线尾!使用 qi::blank相反

• 支持可靠性:

      empty_line          = *blank >> eol;
      comment_line        = *blank >> '#' >> *(char_ - eol) >> (eol|eoi);
      def_first_line      = graph >> +(char_ - eol)         >> (eol|eoi);
      def_subsequent_line = +blank >> +(char_ - eol)        >> (eol|eoi);
  
      definition          = (def_first_line >> *def_subsequent_line);
  
      start               = (  
                              *(comment_line | empty_line | definition)
                            ) [ _val = px::construct<context>() ]
                            ;
  

  这个简单的习惯将节省您数小时的工作时间，并在与 Spirit 合作时保持理智。

• 您可以稍微简化包含

这是一个修复版本 Live On Coliru 输出:

<start>
  <try># comment line\n\nfirs</try>
  <comment_line>
    <try># comment line\n\nfirs</try>
    <success>\nfirst definition li</success>
    <attributes>[[ , c, o, m, m, e, n, t,  , l, i, n, e]]</attributes>
  </comment_line>
  <comment_line>
    <try>\nfirst definition li</try>
    <fail/>
  </comment_line>
  <empty_line>
    <try>\nfirst definition li</try>
    <success>first definition lin</success>
    <attributes>[[]]</attributes>
  </empty_line>
  <comment_line>
    <try>first definition lin</try>
    <fail/>
  </comment_line>
  <empty_line>
    <try>first definition lin</try>
    <fail/>
  </empty_line>
  <definition>
    <try>first definition lin</try>
    <def_first_line>
      <try>first definition lin</try>
      <success>  second \n  third li</success>
      <attributes>[[f, i, r, s, t,  , d, e, f, i, n, i, t, i, o, n,  , l, i, n, e]]</attributes>
    </def_first_line>
    <def_subsequent_line>
      <try>  second \n  third li</try>
      <success>  third line\n\n# anot</success>
      <attributes>[[f, i, r, s, t,  , d, e, f, i, n, i, t, i, o, n,  , l, i, n, e,  ,  , s, e, c, o, n, d,  ]]</attributes>
    </def_subsequent_line>
    <def_subsequent_line>
      <try>  third line\n\n# anot</try>
      <success>\n# another comment l</success>
      <attributes>[[f, i, r, s, t,  , d, e, f, i, n, i, t, i, o, n,  , l, i, n, e,  ,  , s, e, c, o, n, d,  ,  ,  , t, h, i, r, d,  , l, i, n, e]]</attributes>
    </def_subsequent_line>
    <def_subsequent_line>
      <try>\n# another comment l</try>
      <fail/>
    </def_subsequent_line>
    <success>\n# another comment l</success>
    <attributes>[[f, i, r, s, t,  , d, e, f, i, n, i, t, i, o, n,  , l, i, n, e,  ,  , s, e, c, o, n, d,  ,  ,  , t, h, i, r, d,  , l, i, n, e]]</attributes>
  </definition>
  <comment_line>
    <try>\n# another comment l</try>
    <fail/>
  </comment_line>
  <empty_line>
    <try>\n# another comment l</try>
    <success># another comment li</success>
    <attributes>[[]]</attributes>
  </empty_line>
  <comment_line>
    <try># another comment li</try>
    <success></success>
    <attributes>[[ , a, n, o, t, h, e, r,  , c, o, m, m, e, n, t,  , l, i, n, e, !]]</attributes>
  </comment_line>
  <comment_line>
    <try></try>
    <fail/>
  </comment_line>
  <empty_line>
    <try></try>
    <fail/>
  </empty_line>
  <definition>
    <try></try>
    <def_first_line>
      <try></try>
      <fail/>
    </def_first_line>
    <fail/>
  </definition>
  <success></success>
  <attributes>[]</attributes>
</start>
Success

完整代码供引用:

#define BOOST_SPIRIT_DEBUG
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/fusion/include/adapt_struct.hpp>

#include <vector>
#include <iostream>
#include <string>

namespace qi = boost::spirit::qi;

namespace termcxx { namespace parser {

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

    //using qi::double_;
    using ascii::blank;
    //using px::ref;
    using px::construct;

    //using qi::eps;
    //using qi::lit;
    using qi::_val;
    using qi::_1;
    using ascii::char_;
    using ascii::graph;
    using qi::eol;
    using qi::eoi;

    struct context
    {
        int dummy;

        context () = default;
        context (context const &) = default;
        context (std::vector<char> a) { }
        context (std::vector<char> a, std::vector<char> b) { }
    };

} }

BOOST_FUSION_ADAPT_STRUCT(termcxx::parser::context, (int, dummy))

namespace termcxx { namespace parser {

    template <typename Iterator>
    struct parser : qi::grammar<Iterator, context()>
    {
        parser() : parser::base_type(start)
        { 
            empty_line          = *blank >> eol;
            comment_line        = *blank >> '#' >> *(char_ - eol) >> (eol|eoi);
            def_first_line      = graph >> +(char_ - eol)         >> (eol|eoi);
            def_subsequent_line = +blank >> +(char_ - eol)        >> (eol|eoi);

            definition          = (def_first_line >> *def_subsequent_line);

            start               = (  
                                    *(comment_line | empty_line | definition)
                                  ) [ _val = px::construct<context>() ]
                                  ;

            BOOST_SPIRIT_DEBUG_NODES((start)(def_first_line)(def_subsequent_line)(definition)(empty_line)(comment_line))
        }

      private:
        qi::rule<Iterator, context()> start;
        qi::rule<Iterator, std::string()> comment_line;
        qi::rule<Iterator, std::string()> empty_line;
        qi::rule<Iterator, std::string()> def_first_line;
        qi::rule<Iterator, std::string()> def_subsequent_line;
        qi::rule<Iterator, std::string()> definition;
    };

} }

int main()
{
    using It = boost::spirit::istream_iterator;
    termcxx::parser::parser<It> g;

    It f(std::cin >> std::noskipws), l;
    termcxx::parser::context data;
    if (qi::parse(f,l,g,data))
        std::cout << "Success\n";
    else
        std::cout << "Failure\n";

    if (f != l)
        std::cout << "Remaining input: '" << std::string(f,l) << "'\n";
}