增强精神编译问题

大家好，我是boost spirit库的新手。你能告诉我为什么下面的代码不能编译吗?

当我添加"scientificNumber"规则到我的语法它不编译。原因是什么呢?我添加了"scientificNumber"规则，以便能够解析像"12E10"这样的科学符号。我不知道这样做是否正确。

    namespace qi    = boost::spirit::qi;
    namespace phx   = boost::phoenix;
    typedef boost::function<double()> Value;
    #define BINARY_FUNCTOR(name, op)                        
    struct name                                             
    {                                                       
        name(Value x, Value y): x_(x), y_(y) {}               
        double operator()() { return x_() op y_(); }          
        Value x_, y_;                                         
    }; 
    BINARY_FUNCTOR(ADD, +)
    BINARY_FUNCTOR(SUB, -)
    BINARY_FUNCTOR(MUL, *)
    BINARY_FUNCTOR(DIV, /)
    struct LIT
    {
        LIT(double x): x_(x) {}
        double operator()() { return x_; }
        double x_;
    };
    struct NEG
    {
        NEG(Value x): x_(x) {}
        double operator()() { return -x_(); }
        Value x_;
    };
    struct SQRT
    {
        SQRT(Value x): x_(x){}
        double operator()() {return sqrt(x_()); }
        Value x_;
    };
    struct SCIENTIFIC
    {
        SCIENTIFIC(std::wstring x): x_(x){}
        double operator()() {return boost::lexical_cast<double>(x_); }
        std::wstring x_;
    };

    // expression grammar definition
    template <typename It, typename Skipper=boost::spirit::qi::space_type>
    struct parser : boost::spirit::qi::grammar<It, Value(),  Skipper>
    {
        parser() : parser::base_type(expression)
        {
            using namespace qi;
            expression =
                term                    [_val = _1]
                >> *( ('+' >> term  [_val = phx::construct<ADD>(_val, _1)])
                    | ('-' >> term  [_val = phx::construct<SUB>(_val, _1)])
                    );
            term =
                factor                [_val = _1]
                >> *( ('*' >> factor  [_val = phx::construct<MUL>(_val, _1)])
                    | ('/' >> factor  [_val = phx::construct<DIV>(_val, _1)])
                    );
            factor =
                double_               [_val = phx::construct<LIT>(_1)]
                |   scientificNumber  [_val = phx::construct<SCIENTIFIC>(_1)]
                |   '(' >> expression [_val = _1] >> ')'
                |   ('-' >> factor    [_val = phx::construct<NEG>(_1)])
                |   ('+' >> factor    [_val = _1])
                            |   (string("SQRT") >> '(' >> expression [_val = phx::construct<SQRT>(_1)] >> ')');
          scientificNumber = lexeme[+(boost::spirit::qi::digit) >> lit('E') >>  lit('-') >> +(boost::spirit::qi::digit)];

            BOOST_SPIRIT_DEBUG_NODE(expression);
            BOOST_SPIRIT_DEBUG_NODE(term);
            BOOST_SPIRIT_DEBUG_NODE(factor);
        }
      private:
        boost::spirit::qi::rule<It, std::wstring , Skipper> scientificNumber;
        qi::rule<It, Value(), Skipper> expression, term, factor;
    };

        int main()
        {
            std::wstring::const_iterator beginExpression(testExp.begin());
            std::wstring::const_iterator endExpression(testExp.end());
            typedef std::wstring::const_iterator It;
            parser<It , boost::spirit::qi::space_type> expressionParser;
            Value logicExpression;
   phrase_parse(beginExpression,endExpression,expressionParser,boost::spirit::qi::space,logicExpression);
       }

你能告诉我什么是boost::spirit::qi::grammar

如果您只搜索包含 error 的第一行，您将看到以下注释:

            // If you are seeing a compilation error here stating that the
            // fourth parameter can't be converted to a required target type
            // then you are probably trying to use a rule or a grammar with
            // an incompatible skipper type.
            if (f(first, last, context, skipper))

这是bingo:它告诉你什么是错的。它认为std::wstring是船长。

qi::rule<It, std::wstring, Skipper> scientificNumber; // huh?

根据文档，您需要将属性类型拼写为函数签名的返回类型:

qi::rule<It, std::wstring(), Skipper> scientificNumber;

现在，它编译并运行，如下所示，打印输出:

Success: true   Value: 2.7e-09

重要

然而，使用lexical_cast 内部 Boost Spirit…解析一个数字(! ?)是一个滑稽的。您可以让测试原来的东西:它只与LIT (qi::double_)解析器一起工作。参见http://ideone.com/mI1ESI

同样，参见这里的文档:link

#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/lexical_cast.hpp>
namespace qi    = boost::spirit::qi;
namespace phx   = boost::phoenix;
typedef boost::function<double()> Value;
#define BINARY_FUNCTOR(name, op)                        
    struct name                                         
    {                                                   
        name(Value x, Value y): x_(x), y_(y) {}         
        double operator()() { return x_() op y_(); }    
        Value x_, y_;                                   
    };
BINARY_FUNCTOR(ADD, +)
BINARY_FUNCTOR(SUB, -)
BINARY_FUNCTOR(MUL, *)
BINARY_FUNCTOR(DIV, /)
struct LIT
{
    LIT(double x): x_(x) {}
    double operator()()
    {
        return x_;
    }
    double x_;
};
struct NEG
{
    NEG(Value x): x_(x) {}
    double operator()()
    {
        return -x_();
    }
    Value x_;
};
struct SQRT
{
    SQRT(Value x): x_(x) {}
    double operator()()
    {
        return sqrt(x_());
    }
    Value x_;
};
struct SCIENTIFIC
{
    SCIENTIFIC(std::wstring x): x_(x) {}
    double operator()()
    {
        return boost::lexical_cast<double>(x_);
    }
    std::wstring x_;
};

// expression grammar definition
template <typename It, typename Skipper=qi::space_type>
struct parser : qi::grammar<It, Value(),  Skipper>
{
    parser() : parser::base_type(expression)
    {
        using namespace qi;
        expression =
            term                    [_val = _1]
            >> *(('+' >> term       [_val = phx::construct<ADD>(_val, _1)])
                    | ('-' >> term  [_val = phx::construct<SUB>(_val, _1)])
                );
        term =
            factor                  [_val = _1]
            >> *(('*' >> factor     [_val = phx::construct<MUL>(_val, _1)])
                 | ('/' >> factor   [_val = phx::construct<DIV>(_val, _1)])
                );
        factor =
            double_                 [_val = phx::construct<LIT>(_1)]
            |   scientificNumber    [_val = phx::construct<SCIENTIFIC>(_1)]
            | '(' >> expression [_val = _1] >> ')'
            | ('-' >> factor        [_val = phx::construct<NEG>(_1)])
            | ('+' >> factor        [_val = _1])
            | (string("SQRT") >> '(' >> expression [_val = phx::construct<SQRT>(_1)] >> ')');
        scientificNumber = lexeme[+(qi::digit) >> lit('E') >>  lit('-') >> +(qi::digit)];
        BOOST_SPIRIT_DEBUG_NODE(expression);
        BOOST_SPIRIT_DEBUG_NODE(term);
        BOOST_SPIRIT_DEBUG_NODE(factor);
    }
    private:
    qi::rule<It, std::wstring(), Skipper> scientificNumber;
    qi::rule<It, Value(), Skipper> expression, term, factor;
};

int main()
{
    const std::wstring testExp = L"3E-10*(12-3)";
    typedef std::wstring::const_iterator It;
    It f(testExp.begin()), e(testExp.end());
    parser<It, qi::space_type> expressionParser;
    Value logicExpression;
    bool ok = phrase_parse(f,e,expressionParser,qi::space,logicExpression);
    std::cout << "Success: " << std::boolalpha << ok << "tValue: " << logicExpression() << 'n';
}

编译问题就在这里:

 boost::spirit::qi::rule<It, std::wstring , Skipper> scientificNumber;

它不产生任何属性，因为您没有提供构造函数。修复方法如下:

 boost::spirit::qi::rule<It, std::wstring() , Skipper> scientificNumber;

关于boost::spirit::qi::grammar，请查看:http://www.boost.org/doc/libs/1_53_0/libs/spirit/classic/doc/grammar.html

这里有很多例子:
https://stackoverflow.com/questions/tagged/boost-spirit

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