所以我有一个解析器,它将7.5 * [someAlphanumStr]或7.5 [someAlphanumStr]等字符串解析为此结构:
struct summand { float factor; std::string name; summand(const float & f):factor(f), name(""){} summand(const std::string & n):factor(1.0f), name(n){} summand(const float & f, const std::string & n):factor(f), name(n){} summand():factor(0.0f), name(""){}};
但另外我需要能够解析像[someAlphanumStr] * 7.4,[someAlphanumStr] 5,7.4和[someAlphanumStr]这样的字符串.在最后两种情况下(7.4和[someAlphanumStr])我想设置被省略为默认值的字段的值,为此我已经为我的struct summand构造函数编写了一个参数.
下面是我生成的代码和结果:
#include <boost/config/warning_disable.hpp>#include <boost/spirit/include/qi.hpp>#include <boost/fusion/include/adapt_struct.hpp>#include <boost/fusion/include/io.hpp>#include <iostream>#include <string>#include <vector>namespace client{ namespace spirit = boost::spirit; namespace qi = boost::spirit::qi; namespace ascii = boost::spirit::ascii; struct summand { float factor; std::string name; summand(const float & f):factor(f), name(""){} summand(const std::string & n):factor(1.0f), name(n){} summand(const float & f, const std::string & n):factor(f), name(n){} summand():factor(0.0f), name(""){} };}BOOST_FUSION_ADAPT_STRUCT(client::summand, (float, factor) (std::string, name) )namespace client { template <typename Iterator> struct summand_parser : qi::grammar<Iterator, summand(), ascii::space_type> { summand_parser() : summand_parser::base_type(summand_rule) { using namespace ascii; summand_rule %= (qi::float_ >> -qi::lit('*') >> '[' >> qi::lexeme[alpha >> *alnum] >> ']')|('[' >> qi::lexeme[alpha >> *alnum] >> ']' >> -qi::lit('*') >> qi::float_)|(qi::float_)|('[' >> qi::lexeme[alpha >> *alnum] >> ']'); } qi::rule<Iterator, summand(), ascii::space_type> summand_rule; };}void parseSummandsInto(std::string const& str, client::summand& summands){ typedef std::string::const_iterator It; static const client::summand_parser<It> g; It iter = str.begin(), end = str.end(); bool r = phrase_parse(iter, end, g, boost::spirit::ascii::space, summands); if (r && iter == end) return; else throw "Parse failed";}int main(){ std::vector<std::string> inputStrings = {"7.5*[someAlphanumStr]", "7.5[someAlphanumStr]", "[someAlphanumStr]*7.4", "[someAlphanumStr]5", "7.4", "[someAlphanumStr]"}; std::for_each(inputStrings.begin(), inputStrings.end(), [&inputStrings](std::string & inputStr) { client::summand parsed; parseSummandsInto(inputStr, parsed); std::cout << inputStr << " -> " << boost::fusion::as_vector(parsed) << std::endl; });}
结果(Coliru):
clang -std=c 11 -O0 -Wall -pedantic main.cpp ./a.out c filt -t7.5*[someAlphanumStr] -> (7.5 someAlphanumStr)7.5[someAlphanumStr] -> (7.5 someAlphanumStr)[someAlphanumStr]*7.4 -> (115 )[someAlphanumStr]5 -> (115 )7.4 -> (7.4 )[someAlphanumStr] -> (115 omeAlphanumStr)
感谢所有人的明确答案和建议,特别是我很感谢@sehe.
解决方法:
使用Spirit [1]完成任何事情的方法是使用小步骤,沿途严格简化.
不要忍受“残酷”(就像随机重复的子表达式).而且,明确是好的.在这种情况下,我首先提取重复的子表达式并重新格式化以便易读:
name_rule = '[' >> qi::lexeme[alpha >> *alnum] >> ']'; factor_rule = qi::float_; summand_rule %= (factor_rule >> -qi::lit('*') >> name_rule) | (name_rule >> -qi::lit('*') >> factor_rule) | (factor_rule) | (name_rule) ;
在那里,已经好多了,我没有改变一件事.可是等等!它不再编译
qi::rule<Iterator, std::string(), ascii::space_type> name_rule; qi::rule<Iterator, float(), ascii::space_type> factor_rule;
事实证明,语法只是“发生”才能编译,因为Spirit的属性兼容性规则是如此宽松/宽松,以至于匹配名称的字符只被分配给因子部分(115来自哪里:0x73是来自s的ASCII) someAlphanumStr).
OOPS / TL; DW我在这里写了一篇很长的分析,曾经,但是我通过关闭我的浏览器来破坏它,所以只有一个旧的草案缓存服务器端:(我现在将它归结为底线:
来源:https://www.icode9.com/content-4-428501.htmlGuideline Use either constructor overloads to assign to your exposed attribute type, or use Fusion Sequence adaptation, but don’t mix the two: they will interfere in surprising/annoying ways.
别担心,我当然不会让你空手而归.我只是“手动”指导因素并在各自的“插槽”(成员)中命名组件[2].
继承属性是一种保持这种清晰易用的甜蜜方式:
// assuming the above rules redefined to take ("inherit") a summand& attribute:qi::rule<Iterator, void(summand&), ascii::space_type> name_rule, factor_rule;
只需在语义操作中添加一个简单的赋值:
name_rule = as_string [ '[' >> lexeme[alpha >> *alnum] >> ']' ] [ _name = _1 ];factor_rule = double_ [ _factor = _1 ];
现在,“魔法尘埃”当然是如何定义_name和_factor的.我更喜欢使用绑定,而不是phx :: at_c< N>由于维护费用:
static const auto _factor = phx::bind(&summand::factor, qi::_r1);static const auto _name = phx::bind(&summand::name, qi::_r1);
看到?这非常简洁,清楚地显示了正在发生的事情.此外,这里没有实际需要使用Fusion适配进行加法.
现在,最后,我们也可以简化主要规则:
summand_rule = factor_rule (_val) >> - ( -lit('*') >> name_rule (_val) ) | name_rule (_val) >> - ( -lit('*') >> factor_rule (_val) ) ;
这样做,只需通过使尾随部分可选,将单分支分支组合成双分支分支.
请注意summand默认构造函数如何处理默认值:
struct summand { float factor; std::string name; summand() : factor(1.f), name("") {}};
注意这是如何消除了相当复杂的.
查看运行Live on Coliru的完全适应的样本打印:
7.5*[someAlphanumStr] -> (7.5 someAlphanumStr)7.5[someAlphanumStr] -> (7.5 someAlphanumStr)[someAlphanumStr]*7.4 -> (7.4 someAlphanumStr)[someAlphanumStr]5 -> (5 someAlphanumStr)7.4 -> (7.4 )[someAlphanumStr] -> (1 someAlphanumStr)
完整的代码清单
#define BOOST_SPIRIT_USE_PHOENIX_V3//#define BOOST_SPIRIT_DEBUG#include <boost/spirit/include/qi.hpp>#include <boost/spirit/include/phoenix.hpp>namespace client { namespace qi = boost::spirit::qi; namespace phx = boost::phoenix; namespace ascii = boost::spirit::ascii; struct summand { float factor; std::string name; summand() : factor(1.f), name("") {} };}namespace client { template <typename Iterator> struct summand_parser : qi::grammar<Iterator, summand(), ascii::space_type> { summand_parser() : summand_parser::base_type(summand_rule) { using namespace ascii; static const auto _factor = phx::bind(&summand::factor, qi::_r1); static const auto _name = phx::bind(&summand::name, qi::_r1); name_rule = qi::as_string [ '[' >> qi::lexeme[alpha >> *alnum] >> ']' ] [ _name = qi::_1 ] ; factor_rule = qi::double_ [ _factor = qi::_1 ] ; summand_rule = factor_rule (qi::_val) >> - ( -qi::lit('*') >> name_rule (qi::_val) ) | name_rule (qi::_val) >> - ( -qi::lit('*') >> factor_rule (qi::_val) ) ; BOOST_SPIRIT_DEBUG_NODES((summand_rule)(name_rule)(factor_rule)) } qi::rule<Iterator, void(summand&), ascii::space_type> name_rule, factor_rule; qi::rule<Iterator, summand(), ascii::space_type> summand_rule; };}bool parseSummandsInto(std::string const& str, client::summand& summand){ typedef std::string::const_iterator It; static const client::summand_parser<It> g; It iter(str.begin()), end(str.end()); bool r = phrase_parse(iter, end, g, boost::spirit::ascii::space, summand); return (r && iter == end);}int main(){ std::vector<std::string> inputStrings = { "7.5*[someAlphanumStr]", "7.5[someAlphanumStr]", "[someAlphanumStr]*7.4", "[someAlphanumStr]5", "7.4", "[someAlphanumStr]", }; std::for_each(inputStrings.begin(), inputStrings.end(), [&inputStrings](std::string const& inputStr) { client::summand parsed; if (parseSummandsInto(inputStr, parsed)) std::cout << inputStr << " -> (" << parsed.factor << " " << parsed.name << ")\n"; else std::cout << inputStr << " -> FAILED\n"; });}
[1]可以说,技术上还有其他任何东西
[2]您可以保留FUSION_ADAPT_STRUCT但不再需要它,如您所见
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