使用boost spirit qi解析器解析enum

Question

我正在嘗試解析char以填寫C ++ 11強類型枚舉。 我需要幫助為枚舉編寫解析器..它也需要高性能。

我有一個格式如下的字符串

Category | Type | Attributes 

例：

std::string str1 = "A|D|name=tim, address=3 infinite loop"
std::string str2 = "A|C|name=poc, address=5 overflow street" 

我代表類別和類型如下：

 enum class CATEGORY : char 
 {
     Animal:'A', Bird:'B'
 } 

 enum class TYPE : char 
 {
     Dog:'D', Bird:'B'
 } 

 struct Zoo
 {
      Category category; 
      Type     type; 
      std::string name;
      std::string address;
 }; 

namespace qi = boost::spirit::qi;
namespace repo = boost::spirit::repository;
namespace ascii = boost::spirit::ascii;
template <typename Iterator>
struct ZooBuilderGrammar :  qi::grammar<Iterator, ascii::space_type>
{
 ZooBuilderGrammar():ZooBuilderGrammar::base_type(start_)
 {
    using qi::char_; 
    using qi::_1;
    using qi::lit 
    using boost::phoenix::ref; 

    //need help here 
    start_=char_[/*how to assign enum */ ]>>'|'
         >>char_[ /*how to assign enum */ ]>>'|'
         >>lit;
 } 
 qi::rule<Iterator, ascii::space_type> start_;
};   

我有一個問題是創建一個解析器類型，如內置ex：qi :: char_“解析枚舉CATEGORY和TYPE”。

我在這里先向您的幫助表示感謝..

Answer 1

像往常一樣，有幾種方法：

1. 語義動作方式（ad-hoc）
2. 定制點的方式
3. qi ::符號方式

哪個是最合適的。 這三種方法應該同樣有效。 symbols<> apprach似乎最安全（不涉及強制轉換）和靈活：你可以使用它與可變長度的枚舉成員，在no_case[]等內部使用它。

個案分析：

1. 語義動作方式（ad-hoc） ：

    template <typename Iterator> struct ZooBuilderGrammar : qi::grammar<Iterator, ascii::space_type> { ZooBuilderGrammar():ZooBuilderGrammar::base_type(start_) { using namespace qi; category_ = char_("AB") [ _val = phx::static_cast_<Category>(_1) ]; type_ = char_("DB") [ _val = phx::static_cast_<Type>(_1) ]; start_ = category_ >> '|' > type_; } private: qi::rule<Iterator, Category(), ascii::space_type> category_; qi::rule<Iterator, Type(), ascii::space_type> type_; qi::rule<Iterator, ascii::space_type> start_; }; 

   你可以看到Live On Coliru印刷：

    Parse success: [A, D] Remaining unparsed input '|name=tim, address=3 infinite loop' --------------------------- expected: tag: char-set got: "C|name=poc, address=5 overflow street" Expectation failure: boost::spirit::qi::expectation_failure at 'C|name=poc, address=5 overflow street' --------------------------- 

   ---

2. 定制點方式 ：

    namespace boost { namespace spirit { namespace traits { template <typename Enum, typename RawValue> struct assign_to_attribute_from_value<Enum, RawValue, typename enable_if<is_enum<Enum>>::type> { static void call(RawValue const& raw, Enum& cat) { cat = static_cast<Enum>(raw); } }; }}} template <typename Iterator> struct ZooBuilderGrammar : qi::grammar<Iterator, Zoo(), ascii::space_type> { ZooBuilderGrammar():ZooBuilderGrammar::base_type(start_) { start_ = qi::char_("AB") > '|' > qi::char_("DB"); } private: qi::rule<Iterator, Zoo(), ascii::space_type> start_; }; 

   看它也住在Coliru ，具有相同的輸出（顯然）

   ---

3. qi::symbols方式 ：

    template <typename Iterator> struct ZooBuilderGrammar : qi::grammar<Iterator, Zoo(), ascii::space_type> { ZooBuilderGrammar():ZooBuilderGrammar::base_type(start_) { start_ = category_ > '|' > type_; } private: struct Category_ : qi::symbols<char,Category> { Category_() { this->add("A", Category::Animal)("B", Category::Bird); } } category_; struct Type_ : qi::symbols<char,Type> { Type_() { this->add("D", Type::Dog)("B", Type::Bird); } } type_; qi::rule<Iterator, Zoo(), ascii::space_type> start_; }; 

   看到Live On Coliru

---

完整的演示

這恰好是traits方法，但您可以將骨架重用於其他語法：

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

enum class Category : char { Animal='A', Bird='B' };
enum class Type     : char { Dog='D',    Bird='B' };

struct Zoo {
    Category category;
    Type     type;
}; 

BOOST_FUSION_ADAPT_STRUCT(Zoo, (Category,category)(Type,type))

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

namespace boost { namespace spirit { namespace traits {
    template <typename Enum, typename RawValue> 
    struct assign_to_attribute_from_value<Enum, RawValue, typename enable_if<is_enum<Enum>>::type> {
        static void call(RawValue const& raw, Enum& cat) {
            cat = static_cast<Enum>(raw);
        }
    };
}}}

template <typename Iterator>
struct ZooBuilderGrammar :  qi::grammar<Iterator, Zoo(), ascii::space_type>
{
    ZooBuilderGrammar():ZooBuilderGrammar::base_type(start_)
    {
        start_ = qi::char_("AB") > '|' > qi::char_("DB");
    } 
private:
    qi::rule<Iterator, Zoo(), ascii::space_type> start_;
};   

/////////////////////////////////////////////////
// For exception output
struct printer {
    typedef boost::spirit::utf8_string string;

    void element(string const& tag, string const& value, int depth) const {
        for (int i = 0; i < (depth*4); ++i) std::cout << ' '; // indent to depth

        std::cout << "tag: " << tag;
        if (value != "") std::cout << ", value: " << value;
        std::cout << std::endl;
    }
};

void print_info(boost::spirit::info const& what) {
    using boost::spirit::basic_info_walker;

    printer pr;
    basic_info_walker<printer> walker(pr, what.tag, 0);
    boost::apply_visitor(walker, what.value);
}
//
/////////////////////////////////////////////////

int main()
{
    typedef std::string::const_iterator It;
    static const ZooBuilderGrammar<It> p;

    for (std::string const str1 : { 
            "A|D|name=tim, address=3 infinite loop",
            "A|C|name=poc, address=5 overflow street" })
    {
        It f(str1.begin()), l(str1.end());

        try {
            Zoo zoo;
            bool ok = qi::phrase_parse(f,l,p,ascii::space,zoo);

            if (ok)
                std::cout << "Parse success: [" << static_cast<char>(zoo.category) << ", " << static_cast<char>(zoo.type) << "]\n";
            else
                std::cout << "Failed to parse '" << str1 << "'\n";

            if (f!=l)
                std::cout << "Remaining unparsed input '" << std::string(f,l) << "'\n";
        } catch(qi::expectation_failure<It> const& x)
        {
            std::cout << "expected: "; print_info(x.what_);
            std::cout << "got: \"" << std::string(x.first, x.last) << '"' << std::endl;
        }
        std::cout << "---------------------------\n";
    }
}

Answer 2

我使用qi :: symbols方式作為sehe的sugested，但這樣可以提高代碼的可讀性：

template <typename Iterator>
struct ZooBuilderGrammar :  qi::grammar<Iterator, Zoo(), ascii::space_type>
{
    ZooBuilderGrammar():ZooBuilderGrammar::base_type(start_)
    {
        category_.add
            ("A", Category::Animal)
            ("B", Category::Bird)
            ;
        type_.add
            ("D", Type::Dog)
            ("B", Type::Bird)
            ;
        start_ = category_ > '|' > type_;
    } 
private:
    qi::symbols<char,Type> category_;
    qi::symbols<char,Category> type_;
    qi::rule<Iterator, Zoo(), ascii::space_type> start_;
};