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c-使用Spirit Qi解析为std :: vector,获取段错误或断言失败

作者:互联网

我使用Spirit Qi作为解析器,将数学表达式解析为表达式树.我跟踪诸如在解析时遇到的符号类型之类的事情,这些符号必须在要解析的文本中声明.即,我正在解析Bertini input files,为简化起见,其简单示例为here,复杂示例为here,如下所示:

%input: our first input file
  variable_group x,y;
  function f,g;

  f = x^2 - 1;
  g = y^2 - 4;
 END;

我一直在努力的语法将理想地

>查找声明语句,然后解析以下用逗号分隔的声明类型的符号列表,并将符号的结果矢量存储在要解析的类对象中;例如variable_group x,y;
>找到一个先前声明的符号,后跟一个等号,并且将该符号定义为可评估的数学对象;例如f = x ^ 2-1-;这部分我大部分处于控制之下.
>找到一个之前未声明的符号,后跟=,然后将其解析为子函数.我想我也可以解决.

我一直在努力解决的问题似乎微不足道,但是经过数小时的搜索,我仍然没有到达那里.我已经阅读了数十个Boost Spirit邮件列表帖子,SO帖子,手册和Spirit本身的标题,但仍然不太了解Spirit Spirit解析的一些关键事项.

这是有问题的基本语法定义,将在system_parser.hpp中使用:

#define BOOST_SPIRIT_USE_PHOENIX_V3 1


#include <boost/spirit/include/qi_core.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <iostream>
#include <string>




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


template<typename Iterator>
struct SystemParser : qi::grammar<Iterator, std::vector<std::string>(), boost::spirit::ascii::space_type>
{


    SystemParser() : SystemParser::base_type(variable_group_)
    {
        namespace phx = boost::phoenix;
        using qi::_1;
        using qi::_val;
        using qi::eps;
        using qi::lit;

        qi::symbols<char,int> encountered_variables;

        qi::symbols<char,int> declarative_symbols;
        declarative_symbols.add("variable_group",0);



        // wraps the vector between its appropriate declaration and line termination.
        BOOST_SPIRIT_DEBUG_NODE(variable_group_);
        debug(variable_group_);
        variable_group_.name("variable_group_");
        variable_group_ %= lit("variable_group") >> genericvargp_ >> lit(';');


        // creates a vector of strings
        BOOST_SPIRIT_DEBUG_NODE(genericvargp_);
        debug(genericvargp_);
        genericvargp_.name("genericvargp_");
        genericvargp_ %= new_variable_ % ',';




        // will in the future make a shared pointer to an object using the string
        BOOST_SPIRIT_DEBUG_NODE(new_variable_);
        debug(new_variable_);
        new_variable_.name("new_variable_");
        new_variable_ %= unencountered_symbol_;


        // this rule gets a string.
        BOOST_SPIRIT_DEBUG_NODE(unencountered_symbol_);
        debug(unencountered_symbol_);
        unencountered_symbol_.name("unencountered_symbol");
        unencountered_symbol_ %= valid_variable_name_ - ( encountered_variables | declarative_symbols);


        // get a string which fits the naming rules.
        BOOST_SPIRIT_DEBUG_NODE(valid_variable_name_);
        valid_variable_name_.name("valid_variable_name_");
        valid_variable_name_ %= +qi::alpha >> *(qi::alnum | qi::char_('_') | qi::char_('[') | qi::char_(']') );



    }


    // rule declarations.  these are member variables for the parser.
    qi::rule<Iterator, std::vector<std::string>(), ascii::space_type > variable_group_;
    qi::rule<Iterator, std::vector<std::string>(), ascii::space_type > genericvargp_;
    qi::rule<Iterator, std::string(), ascii::space_type>  new_variable_;
    qi::rule<Iterator, std::string(), ascii::space_type > unencountered_symbol_;// , ascii::space_type


    // the rule which determines valid variable names
    qi::rule<Iterator, std::string()> valid_variable_name_;
};

和一些使用它的代码:

#include "system_parsing.hpp"



int main(int argc, char** argv)
{


    std::vector<std::string> V;
    std::string str = "variable_group x, y, z;";


    std::string::const_iterator iter = str.begin();
    std::string::const_iterator end = str.end();


    SystemParser<std::string::const_iterator> S;


    bool s = phrase_parse(iter, end, S, boost::spirit::ascii::space, V);

    std::cout << "the unparsed string:\n" << std::string(iter,end);


    return 0;
}

它可以在OSX的Clang 4.9.x下编译.当我运行它时,我得到:

断言失败:(px!= 0),函数operator->,文件/usr/local/include/boost/smart_ptr/shared_ptr.hpp,第648行.

或者,如果我使用期望运算符>而不是>>在variable_group_规则的定义中,我得到了我们亲爱的老朋友细分错误:11.

在学习过程中,我遇到了一些很棒的帖子,例如how to tell the type spirit is trying to generateattribute propagationhow to interact with symbolsan example of infinite left recursion会导致段错误,information on parsing into classes, not structs包含使用自定义点的链接(但这些链接中没有示例),the Nabialek trick则将关键字与动作,可能与我要执行的操作最相关dynamic difference parsing,这肯定是我所需要的,因为符号集不断增长,并且由于已经遇到的符号集开始为空,因此我后来不允许将它们用作另一种类型,并且增长-解析规则是动态的.

所以这就是我的位置.我当前的问题是此特定示例生成的断言/段错误.但是,我在某些事情上还不清楚,需要指导性意见,我只是没有从我咨询过的任何资料中收集到指导意见,而希望该要求使该SO问题与之前提出的其他问题脱节的请求是:

>什么时候使用lexeme?我只是不知道何时使用lexeme,而不是.
>何时使用>有哪些准则?而不是>&gt ;?
>我已经看过许多Fusion适应示例,其中有一个要解析的结构以及要执行的一组规则.我的输入文件可能会多次出现函数,变量等的声明,它们都需要放在同一位置,所以我需要能够以任意顺序添加到要解析到的终端类对象的字段中, 多次.我想我想对类对象使用getter / setters,因此解析不是构造对象的唯一途径.这有问题吗?

对此初学者的任何建议都是最欢迎的.

解决方法:

您引用符号变量.但是它们是本地人,因此一旦构造函数返回,它们便不存在.这将调用Undefined Behaviour.任何事情都可能发生.

使symmbol表成为该类的成员.

也简化了周围的舞蹈

>船长(请参见Boost spirit skipper issues).该链接还会回答您的_“何时使用lexeme []是适当的.例如,在您的示例中,您在遭遇到的变量| declarative_symbols附近缺少lexeme [].
>调试宏
>运算符%=,以及一些通常未使用的内容
>猜测您不需要符号的映射类型. (因为没有使用int),简化了那里的初始化

演示

Live On Coliru

#define BOOST_SPIRIT_USE_PHOENIX_V3 1
#define BOOST_SPIRIT_DEBUG 1

#include <boost/spirit/include/qi_core.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <iostream>
#include <string>

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

template <typename Iterator, typename Skipper = ascii::space_type>
struct SystemParser : qi::grammar<Iterator, std::vector<std::string>(), Skipper> {

    SystemParser() : SystemParser::base_type(variable_group_) 
    {
        declarative_symbols += "variable_group";

        variable_group_        = "variable_group" >> genericvargp_ >> ';';
        genericvargp_          = new_variable_ % ',';
        valid_variable_name_   = qi::alpha >> *(qi::alnum | qi::char_("_[]"));
        unencountered_symbol_  = valid_variable_name_ - (encountered_variables|declarative_symbols);
        new_variable_          = unencountered_symbol_;

        BOOST_SPIRIT_DEBUG_NODES((variable_group_) (valid_variable_name_) (unencountered_symbol_) (new_variable_) (genericvargp_))
    }
  private:

    qi::symbols<char, qi::unused_type> encountered_variables, declarative_symbols;

    // rule declarations.  these are member variables for the parser.
    qi::rule<Iterator, std::vector<std::string>(), Skipper> variable_group_;
    qi::rule<Iterator, std::vector<std::string>(), Skipper> genericvargp_;
    qi::rule<Iterator, std::string()> new_variable_;
    qi::rule<Iterator, std::string()> unencountered_symbol_; // , Skipper

    // the rule which determines valid variable names
    qi::rule<Iterator, std::string()> valid_variable_name_;
};

//#include "system_parsing.hpp"

int main() {

    using It = std::string::const_iterator;
    std::string const str = "variable_group x, y, z;";

    SystemParser<It> S;

    It iter = str.begin(), end = str.end();
    std::vector<std::string> V;
    bool s = phrase_parse(iter, end, S, boost::spirit::ascii::space, V);

    if (s)
    {
        std::cout << "Parse succeeded: " << V.size() << "\n";
        for (auto& s : V)
            std::cout << " - '" << s << "'\n";
    }
    else
        std::cout << "Parse failed\n";

    if (iter!=end)
        std::cout << "Remaining unparsed: '" << std::string(iter, end) << "'\n";
}

打印

Parse succeeded: 3
 - 'x'
 - 'y'
 - 'z'

标签:boost-spirit-qi,c,parsing,boost,boost-spirit
来源: https://codeday.me/bug/20191013/1910519.html