c++ - 无法编译用 Boost::Spirit 库编写的简单解析器

Question

以下是我无法在 Boost::spirit 库中编译的最小程序。

    #include <iostream>
    #include <string>
    #include <boost/spirit/include/qi.hpp>
    #include <boost/lexical_cast.hpp>
    using namespace boost::spirit;

    template <typename Iterator>
    struct z3_exp_grammars : qi::grammar<Iterator, std::string(), ascii::space_type>
    {
        z3_exp_grammars() : z3_exp_grammars::base_type(text)
        {


            text = qi::int_[qi::_val = boost::lexical_cast<std::string>(qi::_1)];
         }

        qi::rule<Iterator, std::string(), ascii::space_type> text;

    };


    int main(){

        std::string test("3");
            std::string result;
            std::string::const_iterator beg = test.begin();
            std::string::const_iterator end = test.end();
            typedef z3_exp_grammars<std::string::const_iterator> z3_exp_grammars;
            z3_exp_grammars par;
            qi::phrase_parse(beg,end,par,result);
            std::cout<<"Result is "<<result<<std::endl;
}

我希望在变量结果中看到字符串 3，但代码未编译。如果有人能在代码中发现我的错误，而不是查看错误日志(由于模板而非常危险)，那就太好了。感谢您的帮助。

用编译 T.C 给出的相同代码后得到的编译错误更新问题

Test.cpp:9:11: error: expected nested-name-specifier before ‘result_type’
Test.cpp:9:11: error: using-declaration for non-member at class scope
Test.cpp:9:23: error: expected ‘;’ before ‘=’ token
Test.cpp:9:23: error: expected unqualified-id before ‘=’ token
In file included from /home/jaganmohini/Downloads/boost_1_58_0/boost/proto/proto_fwd.hpp:28:0,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/phoenix/core/limits.hpp:26,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/spirit/include/phoenix_limits.hpp:11,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/spirit/home/support/meta_compiler.hpp:16,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/spirit/home/qi/meta_compiler.hpp:14,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/spirit/home/qi/action/action.hpp:14,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/spirit/home/qi/action.hpp:14,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/spirit/home/qi.hpp:14,
                 from /home/jaganmohini/Downloads/boost_1_58_0/boost/spirit/include/qi.hpp:16,
                 from Test.cpp:3:
/home/jaganmohini/Downloads/boost_1_58_0/boost/utility/result_of.hpp: In instantiation of ‘boost::detail::result_of_nested_result<const to_string_, const to_string_(int&)>’:
/home/jaganmohini/Downloads/boost_1_58_0/boost/utility/result_of.hpp:197:1:   instantiated from ‘boost::detail::tr1_result_of_impl<const to_string_, const to_string_(int&), false>’

Answer 1

两个独立的问题:

1. phrase_parse 期望 Skipper 作为其第四个参数。因此，您应该使用 qi::phrase_parse(beg, end, par, ascii::space, result);

2. 您不能在这样的凤凰占位符上使用 boost::lexical_cast。它被热切地评估。你需要 create a lazy function :

   struct to_string_ {
       using result_type = std::string;
       template<class T>
       std::string operator()(const T& arg) const {
           return boost::lexical_cast<std::string>(arg); 
       }
   };
   
   boost::phoenix::function<to_string_> to_string;
   

   做

   text = qi::int_[qi::_val = to_string(qi::_1)];
   

Demo .