我正在尝试解析 terminfo 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,取消注释 [_val = _1]definition 会破坏编译。为什么?我可以修吗?

如果我忽略实际的 terminfo 文件,我希望下面的代码可以解析这种文本:

# 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

最佳答案

你为什么坚持指定 [_val=_1] ?这是多余的,因为默认属性传播会这样做。事实上它很痛,见下文

接下来, (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(它有足够的智能来继续追加)
  • 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)

  • 还,
  • 依赖自动属性传播
  • 时,您可以将 std::vector<char> 替换为 std::string
  • 您可以检测解析器表达式的实际暴露类型: 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 匹配的 eoi 导致在输入结束时无限循环
  • 使用 char_ 也接受空格(使用 graph 代替:)
        def_first_line      = graph >> +(char_ - eol)         >> (eol|eoi);
    
  • 使用 qi::space 也吃行尾!使用 qi::blank 代替
  • 有利于可靠性:
        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>() ]
                              ;
    

    在使用 Spirit 时,这个简单的习惯将节省您数小时的工作和您的理智。
  • 您可以稍微简化包含

  • 这是带有输出的固定版本 Live On Coliru :
    <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";
    }
    

    关于c++ - Boost.Spirit 语法问题,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/24251565/

    10-13 05:58